High Current Rate Research Articles

An air-cooled system with a control strategy for efficient battery thermal management

Air-cooled systems are widely used in electric vehicles for the thermal management of battery packs. Due to the low specific heat capacity of air, design of air-cooled systems is required to improve the temperature uniformity of battery packs. However, structural design of the system cannot meet the requirement of battery thermal management under varying operating conditions. In this study, a parallel air-cooled system with a control strategy is developed for efficient cooling of battery packs under varying operating conditions. The performance of the air-cooled systems with different single flow types is investigated numerically, with the results verified by experiments. A control strategy based on the temperature difference among battery cells is proposed for the system with J-type flow, and the mechanism by which traditional systems fail in temperature difference control is revealed. To address this issue, an efficient thermal management system that integrates different flow types is proposed and relevant control strategy is developed, with decreased widths of the parallel channels on both ends. The proposed system with the control strategy reduces the temperature difference among battery cells by switching the flow type on demand and guiding more cooling air to the battery cell with high temperature. The numerical results of the cases with high current discharge rate and with varying random operating conditions show that the developed system enables the temperature difference to be controlled below 0.5 K after several switches of flow type. The average temperature difference among the battery cells in the developed system is reduced by more than 67% compared to that with J-type flow alone. The proposed system with the relevant control strategy is efficient for thermal management of battery packs under varying operating conditions.

Modified Series Chain Link MMC for Offshore Wind Farms With Boosted AC Voltage: Frequency-Domain Modeling and Submodule Capacitor Voltage Ripple Optimization

Series Chain Link (SCL) converter, a derivative of Modular Multilevel Converter (MMC), offers a very pragmatic grid-feeding converter technology to form HVDC link for offshore wind farms. However, the SCL-MMC incurs high SubModule (SM) Capacitor Voltage Ripple (CVR), demands high current rating switches and needs High Turns-ratio Transformer (HTT). To address these issues, in this paper, bipolar voltage generator-SMs are integrated into the SCL-MMC to realize negative arm-voltage generation capability. The Modified-SCL MMC (MSCL) in conjunction with a modified-switching function utilizes negative arm-voltage to facilitate the boosted AC voltage and improves CVR distribution among SMs. A newly introduced variable &#x2018;<i>g</i>&#x2019;, representing AC voltage boosting, determines the AC voltage gain and HTT requirements. The boost enabled MSCL-MMC, considering its internal dynamics, is modeled using Harmonic State Space (HSS) approach. The developed HSS small-signal impedance model is capable of accurately predicting the resonance peak and frequency. The HSS large-signal model, on the other hand, predicts the presence of 3^rd Harmonic Circulating Current (3-HCC) in the DC-link, accurately, based on which a suitable suppression scheme is proposed. Hence, the proposed complete solution relieves the switch current rating upto 30&#x0025;. Simulation and experimental results are included to validate the theoretical claims.

Fast-Charging Electrode Architecture Optimization through R2R Screen Printing

Creating vertical channels is a viable strategy for reducing the tortuosity and improving the charge transfer kinetics of electrodes, hence enhancing the fast-charge capacity of lithium-ion batteries (LIBs) to actualize fast-charging electrical products. Despite the fact that certain published approaches may directly render channels with electrodes without post-treatment, the control of channels’ diameter and edge distance is a challenge that may be exploited to investigate and optimize the relationship between channels and fast-charging electrodes. Moreover, the intricacy of these methods precludes their industrialization and commercialization. From the perspective of industrial and precision control channels, Roll-to-roll (R2R) screen printing is a simple, cost-effective, industrially scalable, and pattern-customizable continuous additive manufacturing approach for producing vertical channels, reducing the tortuosity of electrodes, and improving their fast-charging capabilities. Low-tortuosity electrodes manufactured by screen printing may be utilized to research the relationship between channel architecture and electrochemical performances of electrodes, as well as to boost and broaden mechanism studies and commercial applications.In this work, we first applied screen printing to design and fabricate vertical channels with a high resolution. Channel arrangements, diameters, and edge distances were meticulously developed and illustrated for LIB electrodes in order to maximize their capacity at high current rates. Applying LiNi0.6Mn0.2Co0.2O2 cathode ink, clear patterns were printed on the Aluminum substrate. By comparing and filtering, we revealed that 1) the staggered configuration enhances the high-rate charge capabilities of electrodes and 2) the channel diameter and edge distances decreasing improve the rate performances of electrodes. Specifically, at 4 and 6 C, the optimized electrode possesses a charge capacity that is two- and seven-times greater than the conventional bar-coated electrodes, respectively. In addition, neutron computed tomography demonstrated that the Li of the screen-printed electrodes was homogeneously spread along the channels during the charge and discharge operations. We believe that optimized channels accelerate ion transfer in the vertical direction, promote ion diffusion in the horizontal direction, and maximize transfer kinetics for electrodes. Although more research is required to improve the greatest resolution of screen printing technology and refine the internal design of screen-printed electrodes, R2R screen printing technology offers a new opportunity for the optimization, industrialization, and commercialization of fast-charging LIBs.

Architecting for Mass Transport: It Is More Than Just Tortuosity

Mass transport is performance-defining across energy storage devices. An example of this limitation is evident in energy dense lithium-ion batteries (LIBs), which develop concentration gradients from insufficient transport of lithium-ions (Li-ions) when operated at high current rates. This results in lowered capacity and energy due to underutilized active material and increased overpotential. The movement of Li-ions, or lack thereof is the root cause of the trade-off that exists between energy and power density in LIBs. To alleviate societal demur towards the full adoption of electric vehicles, range anxiety and slow charging are predominant challenges that industry and academia are rushing to overcome. These goals may require reimagined processing methods to move beyond planar electrodes with disorganized and heterogeneous porosity to create architectures that are dense in active material and contain tailored porosity. To maximize the geometric component of diffusion and species flux, porous low-tortuosity channels are a rational design choice, as they act as mass-transport highways for much needed through-plane Li-ion transport.One such innovative process is hybrid inorganic phase inversion (HIPI), a manufacturing method that is scalable, material-agnostic and results in low-tortuosity free-standing and monolithic architectures with tunable material-to-pore ratios. The HIPI process can enable electrodes with adjustable thicknesses of 100s of µm and relevant micro-architectural feature sizes between 5-40 µm, tailored by tuning the gelation temperature and nucleation density of the inorganic suspension during the nonequilibrium HIPI process. Importantly, the use of a soft organogel casting support results in the unhindered accessibility of the low-tortuosity pores present in the HIPI architectures.HIPI-architected anode and cathode electrodes exhibit electrochemical and architectural stability over a 1000 cycles in a full-cell battery. Further, mass-transport constraints appear at high current densities, and we identify the lithiation step as rate-performance limiting, a result of insufficient Li-ion supply and concentration polarization. Thus, for energy and power dense LIBs the answer is not simply mass-transport highways as unoptimized low-tortuosity channels, rather in-plane Li-ion demands must be tethered to the through-plane transport. Our results demonstrate the need for and feasibility of tailored electrode architectures where dimensional ratios between low-tortuosity channels, the charge-storing matrix, and electrode thickness are tunable, to both understand multi-scale structure-performance relationships and meet coupled power and energy-storage requirements.

An Experimental Method to Measure Electrokinetics of Oxygen Electrodes in High Temperature Solid Oxide Electrolyzers through Symmetrical Cell Configuration

Using high temperature solid oxide electrolytic cells (SOECs) to make hydrogen from steam has thermodynamic advantages in efficiency and yield over its low temperature water electrolyzer counterparts. However, SOECs generally exhibit faster performance degradation than solid oxide fuel cells (SOFCs), thus presenting a major challenge to the technology scale up for mass production of hydrogen. One leading cause for the degradation is associated with the delamination of oxygen electrode (OE), particularly under high current densities or hydrogen production rate. In this presentation, we show our efforts to determine the experimental conditions under which OE can safely operate without delamination. We first show application of DC-biased electrochemical impedance spectroscopy (EIS) method to three-electrode symmetrical cells (STEC) to delineate OE polarization resistance RP and overpotential h as a function of current density (J) and time (t) under both oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) operation modes. From this set of basic data, we extract intrinsic exchange current density (io) of the OE using the “low-field” approximation approach embedded in the classical Butler-Volmer equation. We then correlate the obtained io with time-to-delamination (TTD) defined by the time at which io become zero. We finally establish the analytical relationship between TTD and io for three typical operating current densities ranging from 0.5-1.5 A/cm2, from which the lifetime of SOEC is predicted at a specific H2-producing current density.

Understanding the lithiation intermediates of a silicon-based alloying anode by using operando diffraction and Raman spectroscopic techniques

In the present study, the effect of lithiation on a chalcopyrite phase, cadmium silicon phosphide (CdSiP2) anode is studied. This silicon-based phosphide anode helps in overcoming certain challenges encountered towards the application of elemental silicon anode for lithium-ion battery. Despite of having a fairly high band gap, this material represents outstanding cycling stability for lithium storage. Half-cell configuration results in a capacity of 970 mAh g−1 towards the end of 500 cycles at an applicable rate of 300 mA g−1, whereas a capacity of 645 mAh g−1 is obtained at a rate of 5000 mA g−1 for about 1800 cycles. The rate capability studies suggest highly reversible storage processes when switching from extremely high current rates such as 30 A g−1. Full-cell studies indicate highly stable charge-discharge voltage profiles with an appreciable capacity of around 400 mAh g−1 towards the end of 1400 cycles. Further, in-situ X-ray diffraction (XRD) analysis indicates conversion processes and confirms the formation of phases such as Li3P, LiCdP, Li5SiP3, Li13Si4, Li22Si5 and CdLi at various stages of charge-discharge cycling.

Synthesis ofhigh‐performancemanganese oxide nanorod withZIF67as electrode material forlithium‐ionbatteries

AbstractIntroductionThe demands of the upcoming energy storage technologies are ideally suited for nanomaterials with metal–organic frameworks (MOFs). MOFs are porous materials formed from organic linkers and metal ions offering promising properties for various applications due to their ability to construct finely tunable and homogenous pore architectures.ObjectivesThe primary objective of this study is to synthesize MnO2with zeolitic imidazole framework 67 (ZIF67) and investigate its electrochemical performance.MethodsNanocomposites of MnO2@ZIF67 were successfully synthesized using a two‐step process involving the hydrothermal method followed by the precipitation method. The synthesized MnO2@ZIF67 nanocomposites were characterized using spectroscopic and microscopy techniques, including x‐ray diffractometry (XRD), field emission scanning electron microscopy (FESEM), and high‐resolution transmission electron microscopy (HRTEM).ResultsThe prepared nanocomposite exhibited an excellent specific capacity of 2629 mAh g−1during the first cycle, even at a high current rate of 1C (1000 mA g−1). After undergoing 100 cycles, the MnO2@ZIF67 demonstrated good stability and a reversible capacity of 147.3 mAh g−1at a 1C rate and a remarkable Coulombic efficiency of 96%.ConclusionThe excellent electrochemical performance of the nanocomposite can be attributed to its unique composite structure, which combines porous 3D polyhedra with nanorods. Based on its greater specific capacity, superior cyclability, and improved rate performance, the MnO2@ZIF67 nanocomposite is an effective anode material for lithium‐ion batteries.

Vine Shoots‐Derived Hard Carbons as Anodes for Sodium‐Ion Batteries: Role of Annealing Temperature in Regulating Their Structure and Morphology

AbstractSodium‐ion batteries (SIBs) are considered one of the most promising large‐scale and low‐cost energy storage systems due to the abundance and low price of sodium. Herein, hard carbons from a sustainable biomass feedstock (vine shoots) were synthesized via a simple two‐step carbonization process at different highest temperatures to be used as anodes in SIBs. The hard carbon produced at 1200 °C delivered the highest reversible capacity (270 mAh g−1 at 0.03 A g−1, with an acceptable initial coulombic efficiency of 71 %) since a suitable balance between the pseudographitic domains growth and the retention of microporosity, defects, and functional groups was achieved. A prominent cycling stability with a capacity retention of 97 % over 315 cycles was also attained. Comprehensive characterization unraveled a three‐stage sodium storage mechanism based on adsorption, intercalation, and filling of pores. A remarkable specific capacity underestimation of up to 38 % was also found when a two‐electrode half‐cell configuration was employed to measure the rate performance. To avoid this systematic error caused by the counter/reference electrode polarization, we strongly recommend the use of a three‐electrode setup or a full‐cell configuration to correctly evaluate the anode response at moderate and high current rates.

An investigation of the lattice parameter and micro-strain behaviour of LiMn2O4 coated with LiMn1.5Ni0.5O4 to attain high-rate capability and cycling stability

This research provides new insights on the lattice parameters, development of micro strain, and electrochemical properties of uniquely-designed core-shell structure of the LiMn2O4@LiMn1.5Ni0.5O4 composite. The investigation of lattice expansion and contraction during cycling, and evolution of micro strain, provided a better mechanistic understanding of Li+ diffusion. The LiMn2O4 (LMO) was successfully interfaced with LiMn1.5Ni0.5O4 (LMNO) to modify the surface of spinel LiMn2O4 particles through solution combustion and Pluronic polymer assisted composite synthesis. The unique synthesis approach significantly enhanced the rate capability. The LMO@LMNO composite was characterized using XRD, XPS, TEM, CV and charge/discharge characterization. The material characterization results confirmed that the LMO@LMNO composite had slightly larger lattice parameter (8.24027 Å) compared to the pristine LMO (8.2402 Å) and LMNO (8.18511 Å). The micro-strain of the composite is 2.1 × 10−3 μm/m (LMO@LMNO); this is higher than the individual components 1.28 × 10−3 μm/m (LMO), and 1.22 × 10−3 μm/m (LMNO). As expected, the micro-strain of the composite increased during composite formation which induces defects and microscopic stresses. The LMO@LMNO sample exhibited superior electrochemical properties at all current rates as compared LMO. The LMNO delivered a low capacity for high current rates compared to LMO and LMO@LMNO samples; this was attributed to the unique synthesis approach. The first cycle capacities of LMO, LMNO, and LMO@LMNO, were 101 mAh g−1, 125 mAh g−1, 123 mAh g−1 (0.2C). As expected, the discharge capacities for LMO, LMNO, and LMO@LMNO reduced after 120 cycles to 95 mAh g−1 (94 %), 122 mAh g−1 (97.3 %) and 119 mAh g−1 (96.2 %), respectively. In brief, composite LMO@LMNO core-shell structure exhibited superior electrochemical properties due to the higher Ni ratios coupled with the formation a surface layer.

Performance evaluation of a hydrostatic flow immersion cooling system for high-current discharge Li-ion batteries

A Li-ion battery can experience thermal runaway when its temperature rise and temperature distribution are uneven due to fast charging/discharging and extreme hot/cold ambient temperature conditions. In Electric vehicles, a battery thermal management system is used to address these challenges and assure superior battery pack performance. The conventional methods include air and indirect liquid (cold plate) cooling thermal management systems are influencing the high thermal gradients from the top to bottom of the cell and from the cell to cell in a battery pack. Also, when the battery is being discharged at a high current rate, it is difficult to achieve the expected heat dissipation requirements. In order to solve these issues, this research article provides a hydrostatic flow single-phase dielectric immersion cooling technique for an 18,650 cylindrical cell Li-ion battery. The three-dimensional electrochemical-thermal model of an 18,650-cell submerged in dielectric fluid is designed using a Multiscale, Multi-Dimensional (MSMD) approach with the Newman, Tiedemann, Gu, and Kim (NTGK) model. The accuracy of the numerical results is validated as being within 2 °C with experimental data at 3C discharge rate. The experimental results are exhibited a better cooling effect with a 33 % reduction in temperature rise at 3C battery discharge rate in 25 °C ambient temperature. With respect to both 25 °C and 60 °C ambient temperature conditions, this cooling system has a superior cooling effect of <10 °C temperature rise in a cell during a high current (3C) discharge rate. The study showed that at extremely high current discharge rates and various ambient temperature circumstances, the Li-ion battery submerged in a dielectric coolant provides enhanced cooling performance and uniform temperature distribution on the battery surface compared to natural convection. This article highlighted that the immersion cooling technique is an effective cooling phenomenon during electrical abuse conditions.

Investigation of thermal and mechanical effects during electrically-assisted compression of CoCrFeNiW0.5 high entropy alloy

Electrically-assisted manufacturing (EAM) has many advantages than ambient temperature manufacturing and thermoforming for the building of hard-to-deform alloys. The EAM technique of High entropy alloys (HEAs), a newer alloy category, is an issue worth of research, especially the deformation mechanism in the process of EAM. In the paper, the electrically-assisted compressive mechanical behavior of CoCrFeNiW0.5 HEA composed of face centered cubic phase and μ phase precipitate was studied under current density and strain rate region of 0–40 A/mm2 and 0.0005 s−1-0.1 s−1, respectively. At high current density and strain rate, the reduction of yield stress is remarkable. Electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) techniques were utilized to analyze the effect of current density on the flow stress behaviors and microstructure evolution under plastic deformation. The results show that the introduced electric current enhances the movement and annihilation of dislocations as well as dynamic recovery, resulting in the continuous decrease of flow stress. Additionally, we can clearly observed that the dislocation-free ring or some very low dislocation density regions around the μ phase precipitates, that's because μ phase precipitate can lead to severe lattice distortion and thus increase the electron scattering, and then the local high temperature appeared around the defect regions due to local Joule heating effect, which is recognized as the principal reason leading to the significant decrease of mechanical properties during electrically-assisted compression.

Sustainable and efficient energy storage: A sodium ion battery anode from Aegle marmelos shell biowaste

The utilization of bio-degradable wastes for the synthesis of hard carbon anode materials has gained significant interest for application in rechargeable sodium-ion batteries (SIBs) due to their sustainable, low-cost, eco-friendly, and abundant nature. In this study, we report the successful synthesis of hard carbon anode materials from Aegle marmelos (Bael fruit) shells via a hydrothermal carbonization process followed by calcination at varying temperatures (900 °C and 1000 °C). Structural characterizations using XRD and Raman spectroscopy confirm the formation of hard carbon, while FTIR, XPS, BET, SEM, and TEM characterizations reveal the morphology and surface properties of the synthesized materials. The Aegle marmelos Hard Carbon-900 (AMHC-900) and Aegle marmelos Hard Carbon-1000 (AMHC-1000) cells exhibit high specific discharge capacities of ~223 mAh g−1 and ~212 mAh g−1 at 10 mA g−1, respectively. The cells demonstrate excellent cycling stability, with specific discharge capacities of ~78 mAh g−1 and ~66 mAh g−1 at a high current rate (1000 mA g−1) up to 2500 cycles, respectively, and high coulombic efficiency (~99 %). These findings highlight the potential of utilizing bio-degradable wastes through a hydrothermal carbonization process to produce high-performance hard carbon electrodes for SIBs.

Highly Stable MWCNT@NVP Composite as a Cathode Material for Na-Ion Batteries.

A 3D framework with Nasicon structured polyanionic Na3V2(PO4)3 (NVP) has been emphasized as a leading cathode material for sodium-ion batteries (SIBs) due to its high working voltage plateau, structural stability, and good rate performance. Herein, pristine NVP and MWCNT@NVP composite synthesized via a facile solid-state method are examined and compared as cathode materials for Na-ion batteries. The morphological study confirms the uniform distribution of MWCNTs in the pristine NVP structure. Impedance spectroscopy clearly confirms more diffusion of Na ions for the MWCNT@NVP composite as compared to pristine NVP, considering its diffusion coefficient which directly implies on an increase in specific capacity. MWCNT@NVP (FNV-2) showed specific discharge capacity 110 mAhg-1 at 0.1C current rate which is almost stable at higher current rates with marginal fading. However, the pristine NVP shows capacity loss at a higher current rate. It is noteworthy that the MWCNT@NVP composite shows stable performance with marginal specific capacity fading (1%) compared to pristine (15%). This is because of the mechanical integrity and stability afforded to the composite by the intertwined MWCNT framework in the MWCNT@NVP composite matrix against electrode degradation during the electrochemical reaction. More significantly, even at a higher current rate, that is, at 10 C, the composite recorded a very stable and excellent Columbic efficiency of 97% with a reversible specific capacity of 94 mAhg-1 after 2000 cycles. An enhanced electrochemical performance, that is, rate capability and cycling stability, demonstrates the high potential of the MWCNT@NVP composite for Na-ion storage. Moreover, a sodium-ion full cell with hard carbon demonstrated a reversible capacity of 103 mAhg-1 at C/20 current rate, which clearly demonstrates that MWCNT@NVP is a promising cathode material for sodium-ion batteries.

One pot green synthesis of few-layer graphene (FLG) by simple sonication of graphite and Azardirachta Indica resin in water for high-capacity and excellent cyclic behavior of rechargeable lithium-ion battery

A simple, green, and eco-friend route is employed for the preparation of few-layer graphene using Azardirachta Indica resin (AZIr) in water. In addition, the preparation of the solvent (AZIr) for the exfoliation of graphene involves various steps, including vacuum filtration and surface tension optimization by the capillary rise method. It has been demonstrated that the 4 h sonication effectively exfoliated graphite to form a Few-Layer Graphene (FLG) sheet. Structural, morphological, and surface topographical analysis were performed using X-ray diffraction, Raman spectrum, FTIR spectrum, atomic force microscopy, and Scanning electron microscope. The as-prepared FLG was demonstrated as anode material for lithium-ion batteries¸ exhibiting a high initial capacity of 464 mAh g−1 at 0.1C and excellent cyclic performance of 527 mAh g−1 at 200th cycle with 100 % capacity retention. The maximum capacity of 281 mAh g−1 was achieved when tested at a high current rate of 10C. These results suggest that few-layer graphene is a promising material for high-performance Li-ion battery applications.

Enhancing the Integral Structural and Thermal Stability of Ultrahigh-Ni Cathodes via Morphology Refinement and In Situ Interfacial Engineering.

Nickel-rich layered oxides are promising cathodes in commercial materials for lithium-ion batteries. However, the increase of the nickel content leads to the decay of cyclic performance and thermal stability. Herein, in situ surface-fluorinated W-doping LiNi0.90Co0.05Mn0.05O2 cathodes enhance integral lithium-ion migration (transfer in bulk and diffusion in the interface) kinetics by synergistically solving the problems of bulk and interface structural degradation. Owing to the introduction of tungsten, the growth of primary particles is regulated toward the (003) crystal plane and with the acicular structure, which further stabilizes the bulk structure during cycling. Moreover, the LiF coating layer on the cathode/electrolyte interface physically isolates the attack of the electrolyte on the surface cathodes and accelerates the lithium-ion diffusion rate, ultimately ameliorating the interfacial dynamics and structural stability. Dual-modified LiNi0.90Co0.05Mn0.05O2 exhibits superior electrochemical properties, especially more remarkable cyclic retention (88.16% vs 70.44%) after 100 cycles at 1 C and more outstanding high current rate properties (173.31 mAh·g-1 vs 135.97 mAh·g-1) at 5 C than the pristine one. This work emphasizes the probability of an integrated optimization strategy for Ni-rich materials, which provides an innovative idea for ameliorating (bulk and interfacial) structure degradation and promoting the diffusion of lithium ions during cycling.

Nickel-doped Nb18W16O93 nanowires with improved electrochemical properties for lithium-ion battery anodes

Recently, niobium tungsten oxide nanowires have been reported to be a promising anode material for lithium-ion batteries (LiBs). This material has demonstrated high theoretical capacity, significant structural stability, high power density, and environmental friendliness. Nonetheless, its low electronic conductivity is a significant drawback that needs to be addressed. More so, it is desirable to enhance its electrochemical performance to meet the needs of current energy applications. In this study, pristine and nickel-doped (Ni = 1 wt%, 3 wt%, 5 wt%) niobium tungsten oxide nanowires were fabricated using the electrospinning technique, followed by annealing. The effect of nickel doping content on the morphology, structure, and electrochemical performance of niobium tungsten oxide nanowires was investigated. The XRD results show that the Ni doping expanded the unit cell and enhanced the lithium-ion diffusion in the Nb18W16O93 nanowires. The electrochemical test results indicate that the 3 wt% nickel-doped condition exhibits remarkable capacity retention of 93.1% over 500 cycles at a high current rate of 5 C. Furthermore, the Ni doping significantly enhanced the electronic conductivity compared to the pristine Nb18W16O93 nanowires. The results obtained from the CV test also show that Ni doping lowered the polarization and increased the lithium-ion diffusion coefficient.

Sodium and potassium ion storage in cation substituted 2D MoWSe2: insights into the effects of upper voltage cut-off

The superior properties, such as large interlayer spacing and the ability to host large alkali-metal ions, of two-dimensional (2D) materials based on transition metal di-chalcogenides (TMDs) enable next-generation battery development beyond lithium-ion rechargeable batteries. In addition, compelling but rarely inspected TMD alloys provide additional opportunities to tailor bandgap and enhance thermodynamic stability. This study explores the sodium-ion (Na-ion) and potassium-ion (K-ion) storage behavior of cation-substituted molybdenum tungsten diselenide (MoWSe2), a TMD alloy. This research also investigates upper potential suspension to overcome obstacles commonly associated with TMD materials, such as capacity fading at high current rates, prolonged cycling conditions, and voltage polarization during conversion reaction. The voltage cut-off was restricted to 1.5 V, 2.0 V, and 2.5 V to realize the material’s Na+ and K+ ion storage behavior. Three-dimensional (3D) surface plots of differential capacity analysis up to prolonged cycles revealed the convenience of voltage suspension as a viable method for structural preservation. Moreover, the cells with higher potential cut-off values conveyed improved cycling stability, higher and stable coulombic efficiency for Na+ and K+ ion half-cells, and increased capacity retention for Na+ ion half-cells, respectively, with half-cells cycled at higher voltage ranges.

Enhanced rate and specific capacity in nanorod-like core-shell crystalline NiMoO4@amorphous cobalt boride materials enabled by Mott-Schottky heterostructure as positive electrode for hybrid supercapacitors

The supercapacitor electrode materials suffer from structure pulverization and sluggish electrode kinetics under high current rates. Herein, a unique NiMoO4@Co-B heterostructure composed of highly conductive Co-B nanoflakes and a semiconductive NiMoO4 nanorod is designed as an electrode material to exert the energy storage effect on supercapacitors. The formed Mott-Schottky heterostructure is helpful to overcome the ion diffusion barrier and charge transfer resistance during charging and discharging. Moreover, this crystalline-amorphous heterogeneous phase could provide additional ion storage sites and better strain adaptability. Remarkably, the optimized NiMoO4@Co-B hierarchical nanorods (the mass ratio of NiMoO4/Co-B is 3:1) present greatly enhanced electrochemical characteristics compared with other components, and show superior specific capacity of 236.2 mA h g−1 at the current density of 0.5 A g−1, as well as remarked rate capability. The present work broadens the horizons of advanced electrode design with distinct heterogeneous interface in other energy storage and conversion field.

Lean-water hydrogel electrolyte for zinc ion batteries

Solid polymer electrolytes (SPEs) and hydrogel electrolytes were developed as electrolytes for zinc ion batteries (ZIBs). Hydrogels can retain water molecules and provide high ionic conductivities; however, they contain many free water molecules, inevitably causing side reactions on the zinc anode. SPEs can enhance the stability of anodes, but they typically possess low ionic conductivities and result in high impedance. Here, we develop a lean water hydrogel electrolyte, aiming to balance ion transfer, anode stability, electrochemical stability window and resistance. This hydrogel is equipped with a molecular lubrication mechanism to ensure fast ion transportation. Additionally, this design leads to a widened electrochemical stability window and highly reversible zinc plating/ stripping. The full cell shows excellent cycling stability and capacity retentions at high and low current rates, respectively. Moreover, superior adhesion ability can be achieved, meeting the needs of flexible devices.

Development of P3-type K0.70[Cr0.86Sb0.14]O2 cathode for high-performance K-ion batteries

Potassium-ion batteries (KIBs) are one of the most promising alternatives to lithium-ion batteries because of the high standard hydrogen electrode of K+/K, which is the second lowest after lithium. However, the large ionic size of K+ generally hinders the reversible intercalation and results in the undesirable structural changes during charge-discharge process. Thus, it is very important to develop stable cathode materials that accommodate K+ into their crystal structure with minimal structural changes. Here we propose P3-type K0.70 [Cr0.86Sb0.14]O2 as a potential cathode material for high-performance KIBs. The P3-type K0.70 [Cr0.86Sb0.14]O2 was successfully fabricated via electrochemical ion-exchange of Na+/K+. At a current density of 15 mA/g, P3–K0.70 [Cr0.86Sb0.14]O2 delivered a reversible capacity of 126.1 mAh/g with a high coulombic efficiency of 98.7%, corresponding to the de/intercalation of 0.57 mol of K+ ions from/into the structure. In addition, P3-type K0.70 [Cr0.86Sb0.14]O2 showed excellent cycling stability over 200 cycles at a current density of 150 mA/g and power capability even at high current rate of 750 mA/g. In contrast, P3-KxCrO2 demonstrates inferior electrochemical properties; this comparison implies that substitution of 0.14 mol Sb into Cr sites significantly improves structural stability with reversible Cr3+/4+ redox reaction during charge-discharge process.