Average Open Voltage Research Articles

An Advanced High‐Entropy Fluorophosphate Cathode for Sodium‐Ion Batteries with Increased Working Voltage and Energy Density (Adv. Mater. 14/2022)

Sodium-Ion Batteries Cathode materials are decisive for the development of sodium-ion batteries (SIBs). In article number 2110108, Xing-Long Wu and co-workers present a high-entropy Na3V2(PO4)2F3-based cathode for advanced SIBs. The high-entropy effect endows this cathode material with a lowered Na+ migration barrier and enhanced electronic conductivity, which jointly promote charge transport and sodium-storage ability in the phosphate cathode, thereby enhancing the average operating voltage and energy density of the SIB.

P2‐Na2/3Ni2/3Te1/3O2 Cathode for Na‐ion Batteries with High Voltage and Excellent Stability

Air‐stable layered structured cathodes with high voltage and good cycling stability are highly desired for the practical application of Na‐ion batteries. Herein, we report a P2‐Na2/3Ni2/3Te1/3O2 cathode that is stable in ambient air with an average operating voltage of ~3.8 V, demonstrating excellent cycling stability with a capacity retention of more than 92.7% after 500 cycles at 20 mA g−1 and good rate capability with 91.9% capacity utilization at 500 mA g−1 with respect to capacity at 5 mA g−1 between 2.0 and 4.0 V. When the upper cutoff voltage is increased to 4.4 V, P2‐Na2/3Ni2/3Te1/3O2 delivers a reversible capacity of 71.9 mAh g−1 and retains 91.8% of the capacity after 100 cycles at 20 mA g−1. The charge compensation during charge/discharge is mainly due to the redox couple of Ni2+/Ni3+ in the host with a small amount of contribution from oxygen. The stable structure of the material without phase transformation and with small volume change during charge‐discharge allows it to give excellent cycle performance especially when the upper cutoff voltage is not higher than 4.2 V.

A Graphite∥PTCDI Aqueous Dual-Ion Battery.

A full cell chemistry of aqueous dual-ion battery (DIB) was reported, comprising the graphite cathode and 3,4,9,10-perylenetetracarboxylic diimide (PTCDI) as the anode. This DIB employed a mixture aqueous electrolyte: 5 m tributylmethylammonium (TBMA) chloride plus 5 m MgCl2 , where [MgCl3 ]- and TBMA+ serve as the charge carriers for cathode and anode of the DIB, respectively. This novel full cell exhibited a specific capacity of around 41 mAh g-1 based on the total active mass of both electrodes with an average operation voltage of 1.45 V and stable cycling for 400 cycles.

Palmyra Palm tree biomass-derived carbon low-voltage plateau region capacity on Na-ion battery and its full cell performance

Biomass-derived carbon has been proven to be a reliable negative electrode material for cost-effective sodium-ion battery assembly. Although biomass carbons appropriate for the sodium ion insertion and de-insertion in its randomly arranged graphitic structure, though, to obtain a plateau region capacity remains a challenge. Because the anode low-voltage plateau region capacity is highly influenced by the cell voltage and reversible Na+ intercalation. In this work, biomass carbon is produced from fiber-rich palmyra palm tree (PP-C) leaf stalk by simple carbonization. As prepared PP-C degree of graphitic behavior and surface morphology is examined by X-ray diffraction pattern and scanning electron (SEM) microscopy. The PP-C exhibited irregular microparticles and appropriate d002 spacing (3.9 Å) for Na+ ion intercalation. The obtained PP-C specific surface area and pore sizes are 190 m2 g−1 and 4–24 nm, respectively. The exchange current density (I0) of PP-C anode fresh cell and after discharge/charge (100 cycles) calculated 0.057 and 0.048 mA cm−1, respectively. The unique porous nature and extended interlayer distance of PP-C revealed a capacity of 255 mAh g−1 (C/50) and high coulombic efficiency (CE) of 97% and cyclic stability to be 60%. The excellent Na+ intercalation-deintercalation property of PP-C anode paired with a cathode Na3V2(PO4)3 and were assembled as a full-cell sodium-ion battery which demonstrates that the feasibility of high stable average operating voltage 3.35 V. As-fabricated PP-C//Na3V2(PO4)3 full-cell exhibited low polarization approximately 39 mV. From this finding, we believe that the PP-C anode material is promising for sodium-ion battery practical applications.

Surface Engineering Strategy Using Urea To Improve the Rate Performance of Na2 Ti3 O7 in Na-Ion Batteries.

Na2Ti3O7 (NTO) is considered a promising anode material for Na‐ion batteries due to its layered structure with an open framework and low and safe average operating voltage of 0.3 V vs. Na+/Na. However, its poor electronic conductivity needs to be addressed to make this material attractive for practical applications among other anode choices. Here, we report a safe, controllable and affordable method using urea that significantly improves the rate performance of NTO by producing surface defects such as oxygen vacancies and hydroxyl groups, and the secondary phase Na2Ti6O13. The enhanced electrochemical performance agrees with the higher Na+ ion diffusion coefficient, higher charge carrier density and reduced bandgap observed in these samples, without the need of nanosizing and/or complex synthetic strategies. A comprehensive study using a combination of diffraction, microscopic, spectroscopic and electrochemical techniques supported by computational studies based on DFT calculations, was carried out to understand the effects of this treatment on the surface, chemistry and electronic and charge storage properties of NTO. This study underscores the benefits of using urea as a strategy for enhancing the charge storage properties of NTO and thus, unfolding the potential of this material in practical energy storage applications.

Low-cost and high-power K4[Mn2Fe](PO4)2(P2O7) as a novel cathode with outstanding cyclability for K-ion batteries

K4[Mn2Fe](PO4)2(P2O7) exhibits outstanding power-capability and stable cycle performance, with an average operation voltage of ∼3.5 V (vs. K+/K).

An exceptionally large energy cathode with the K–SO4–Cu conversion reaction for potassium rechargeable batteries

A nano-sized CuSO4/carbon (N-CSO/C) composite achieves outstanding electrochemical performances with a high average operating voltage of ∼2.8 V (vs. K+/K).

Naphthalene dianhydride organic anode for a 'rocking-chair' zinc-proton hybrid ionbattery.

Rechargeable batteries consisting of a Zn metal anode and a suitable cathode coupled with a Zn2+ ion-conducting electrolyte are recently emerging as promising energy storage devices for stationary applications. However, the formation of high surface area Zn (HSAZ) architectures on the metallic Zn anode deteriorates their performance upon prolonged cycling. In this work, we demonstrate the application of 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTCDA), an organic compound, as a replacement for the Zn-metal anode enabling the design of a 'rocking-chair'zinc-proton hybrid ion battery. The NTCDA electrode material displays a multi-plateau redox behaviour, delivering a specific discharge capacity of 143 mA h g-1 in the potential window of 1.4 V to 0.3 V vs. Zn|Zn2+. The detailed electrochemical characterization of NTCDA in various electrolytes (an aqueous solution of 1 M ZnOTF, an aqueous solution of 0.01 M H2SO4, and an organic electrolyte of 0.5 M ZnOTF/acetonitrile) reveals that the redox processes leading to charge storage involve a contribution from both H+ and Zn2+. The performance of NTCDA as an anode is further demonstrated by pairing it with a MnO2 cathode, and the resulting MnO2||NTCDA full-cell (zinc-proton hybrid ionbattery) delivers a specific discharge capacity of 41 mA h gtotal-1 (normalized with the total mass-loading of both anode and cathode active materials) with an average operating voltage of 0.80 V.

Dual-Manipulation on P2-Na0.67Ni0.33Mn0.67O2 Layered Cathode toward Sodium-Ion Full Cell with Record Operating Voltage Beyond 3.5 V

ABSTRACT P2-type Na0.67Ni0.33Mn0.67O2, a typical layered transition metal oxide, has been extensively studied as future practical sodium ion batteries cathode due to the merit of high energy density. However, its inferior cyclability and poor rate capability have severely hindered its practical applications. Herein, a stable P2-Na0.67Ni0.23Mg0.1Mn0.67O2 layered cathode with simultaneously achieving magnesium doping and hierarchical one-dimensional nanostructure composed of nanoplate subunits assembly is reported. In-situ X-ray diffraction measurement and diffusion kinetics analysis reveal that Mg ion doping restrains the P2-O2 phase transition and reduces the activation energy of interfacial charge transfer. In addition, the hierarchical nanostructure is shown to possess robust structure, which raises the capacity retention from 74.8% to 92.2% over 150 cycles when compared with its bulk counterpart. Owing to the combined advantages, this unique material exhibits extraordinary electrochemical performance with a high capacity retention of 90.9% over 1000 cycles at 5C in half cell. More importantly, the full cell could achieve the highest average operating voltage of 3.56 V and outstanding energy density of 249.9 Wh kg−1 compared with previously reported state-of-the-art values based on layered oxide cathodes. This work may open up a new opportunity for developing high energy SIBs with practicability.

Composite Paam-Based Hydrogel Electrolyte for Hybrid Aqueous (Zn-Li-ion) Battery

Hybrid aqueous rechargeable batteries are very attractive alternative to conventional rechargeable lithium ion batteries for stationary application because of production and usage safety, reduced production cost and environmental friendliness. Previously aqueous rechargeable batteries with Zn/LiCl-ZnCl2/LiFePO4 system with liquid electrolyte has been reported [1]. The system performed a high rate capability up to 60 C with the average operation voltage 1.2 V and cycling performance with a capacity retention of 80 % over 400 cycles at 6 C.However, there are several drawbacks including water decomposition and zinc dendrite formation hindering the commercialization [1]. The present study aimed to develop a PAAm-based hydrogel electrolyte with inclusion of montmorillonite and halloysite clay nanoparticles for hybrid aqueous rechargeable zinc/lithium ion batteries to overcome above mentioned problems. Polyacrylamide hydrogel was chosen because of its high ionic conductivity, high water content and simple fabrication method in which cross-linking degree, thickness, etc. were optimized. Inclusion of clay could improve mechanical stability of hydrogel electrolyte, prevent water decomposition and dendrite formation.All tests performed in Zn/LiFePO4 cell operating in an optimized LiCl/ZnCl2 aqueous electrolyte based hydrogel. Acknowledgement This research was supported by Faculty-development competitive research grant “Development of safe and high performance flexible Li-ion batteries” #110119DF4514 from Nazarbayev University. References N.Yesbolati, N.Umirov, A.Koishybay, M.Omarova, I.Kurmanbayeva, Y.Zhang, Y.Zhao, Z.Bakenov. Electrochimica Acta, 152 (2015), 505–511.

A High-Quality Monoclinic Nickel Hexacyanoferrate for Aqueous Zinc–Sodium Hybrid Batteries

Aqueous rechargeable batteries (ARBs) are expected to be used in future energy storage systems (ESSs) because of their nontoxicity, nonflammability, and ultrahigh ionic conductivity. However, their low energy density and poor cycle stability are two main drawbacks restricting their application. In this work, we synthesized a highly crystalline monoclinic nickel hexacyanoferrate (NiHCF) and used it in aqueous zinc–sodium hybrid batteries. Because of its low Fe(CN)6 vacancy amount and low water content, the monoclinic NiHCF exhibits high specific capacity and excellent cycle and rate performance. The assembled AZSHBs show excellent electrochemical performance, with an average operating voltage up to 1.464 V, high energy density of 99.1 Wh kg–1, and good cycling stability with 91% capacity retention after 1000 cycles.

High-power rhombohedral-Fe2(SO4)3 with outstanding cycle-performance as Fe-based cathode for K-ion batteries

We report rhombohedral-Fe2(SO4)3 as a promising cathode material for potassium-ion batteries. Detailed structure information for rhombohedral-Fe2(SO4)3 was obtained using X-ray diffraction with Rietveld refinement. Based on the structural information, possible atomic sites for K ions and ion diffusion pathway in the structure were determined using bond-valence energy landscape analyses. At C/20 (1C = 112 mA g−1), rhombohedral-KxFe2(SO4)3 delivered a specific capacity of ~100 mAh g−1 an average operation voltage of ~3.3 V (vs. K+/K), corresponding to reversible de/intercalation of ~1.78 mol K+ ions. Moreover, even at 5C, rhombohedral-KxFe2(SO4)3 exhibited capacity retention of ~80% of the capacity measured at C/20, indicating the outstanding power-capability. After 300 cycles at 2C, rhombohedral-KxFe2(SO4)3 maintained ~83% of its initial specific capacity with high Coulombic efficiency of more than 99%. Operando XRD analyses revealed that the XRD peaks of rhombohedral KxFe2(SO4)3 monotonously shifted during K+ de/intercalation, indicating a single phase reaction. First-principles calculation confirmed the good agreement between the theoretical properties of rhombohedral-KxFe2(SO4)3 and the experimental results, including the average operation voltage, power-capability, and phase reaction.

An In Situ Cross-Linked Nonaqueous Polymer Electrolyte for Zinc-Metal Polymer Batteries and Hybrid Supercapacitors.

This work reports the facile synthesis of nonaqueous zinc-ion conducting polymer electrolyte (ZIP) membranes using an ultraviolet (UV)-light-induced photopolymerization technique, with room temperature (RT) ionic conductivity values in the order of 10-3 S cm-1 . The ZIP membranes demonstrate excellent physicochemical and electrochemical properties, including an electrochemical stability window of >2.4V versus Zn|Zn2+ and dendrite-free plating/stripping processes in symmetric Zn||Zn cells. Besides, a UV-polymerization-assisted in situ process is developed to produce ZIP (abbreviated i-ZIP), which is adopted for the first time to fabricate a nonaqueous zinc-metal polymer battery (ZMPB; VOPO4 |i-ZIP|Zn) and zinc-metal hybrid polymer supercapacitor (ZMPS; activated carbon|i-ZIP|Zn) cells. The VOPO4 cathode employed in ZMPB possesses a layered morphology, exhibiting a high average operating voltage of ≈1.2V. As compared to the conventional polymer cell assembling approach using the ex situ process, the in situ process is simple and it enhances the overall electrochemical performance, which enables the widespread intrusion of ZMPBs and ZMPSs into the application domain. Indeed, considering the promising aspects of the proposed ZIP and its easy processability, this work opens up a new direction for the emergence of the zinc-based energy storage technologies.

Exceptionally high-energy tunnel-type V1.5Cr0.5O4.5H nanocomposite as a novel cathode for Na-ion batteries

Abstract We report a tunnel-type V1.5Cr0.5O4.5H/carbon-nanotube (T-VCr/C) nanocomposite as a new high-energy cathode material for sodium-ion batteries. Structural analyses using Rietveld refinement and bond-valence-energy landscape analysis based on X-ray diffraction reveal the Na+ diffusion paths and possible atomic sizes of Na+ in the V1.5Cr0.5O4.5H structure. Through combined studies using first-principles calculations and various experimental techniques, we confirm that the T-VCr/C nanocomposite delivers a large specific capacity of ~306 mAh g−1, corresponding to 2 mol Na+ de/intercalation at 15 mA g−1, with an average operation voltage of ~2.5 V (vs. Na+/Na) in the voltage range of 1.0–4.0 V based on reversible V3+/V4+ and Cr3+/Cr4+ redox reactions. Even at 900 mA g−1, the T-VCr/C nanocomposite retains a specific capacity of ~214.9 mAh g−1, corresponding to ~70.2% of the capacity measured at 15 mA g−1. Furthermore, over 100 cycles at 300 mA g−1, the T-VCr/C nanocomposite exhibits capacity retention of ~77.1% compared with the initial capacity. Operando/ex-situ X-ray diffraction and X-ray absorption spectroscopy analyses reveal the small structural change of NaxV1.5Cr0.5O4.5H (0 ≤ x ≤ 2) during Na+ de/intercalation based on V4+/V3+ and Cr4+/Cr3+ redox reaction, leading to the outstanding electrochemical performance of the T-VCr/C nanocomposite.

Achieving the Stable Structure and Superior Performance of Na3V2(PO4)2O2F Cathodes via Na-Site Regulation

Na3V2(PO4)2O2F (NVPOF) is considered as a promising cathode material for sodium-ion batteries due to its high structural stability and high average operating voltage (3.8 V). However, its low elect...

Effect of thermal cycling on durability of a solid oxide fuel cell stack with external manifold structure

A 5-cell stack with external manifold is thermal cycled between room temperature and 750 °C fifteen times. The electric performances after each cycle are measured and compared. The stack has an initial peak output of 328.44 W and shows excellent stability in thermal cycling. The average operating voltage degradation rate is only 0.8% corresponding each thermal cycle. A cell from the stack is randomly chosen for electrochemical evaluation. Its performance is found to be comparable to a cell which is not thermal cycled. Post-test examination shows deterioration of cathode contact materials at points of contact and cracks throughout the oxide layer between corrugated and bipolar plates to be the main causes of the degradation.

High‐Voltage Oxygen‐Redox‐Based Cathode for Rechargeable Sodium‐Ion Batteries

AbstractRecently, anionic‐redox‐based materials have shown promising electrochemical performance as cathode materials for sodium‐ion batteries. However, one of the limiting factors in the development of oxygen‐redox‐based electrodes is their low operating voltage. In this study, the operating voltage of oxygen‐redox‐based electrodes is raised by incorporating nickel into P2‐type Na2/3[Zn0.3Mn0.7]O2 in such a way that the zinc is partially substituted by nickel. As designed, the resulting P2‐type Na2/3[(Ni0.5Zn0.5)0.3Mn0.7]O2 electrode exhibits an average operating voltage of 3.5 V and retains 95% of its initial capacity after 200 cycles in the voltage range of 2.3–4.6 V at 0.1C (26 mA g−1). Operando X‐ray diffraction analysis reveals the reversible phase transition: P2 to OP4 phase on charge and recovery to the P2 phase on discharge. Moreover, ex situ X‐ray absorption near edge structure and X‐ray photoelectron spectroscopy studies reveal that the capacity is generated by the combination of Ni2+/Ni4+ and O2−/O1− redox pairs, which is supported by first‐principles calculations. It is thought that this kind of high voltage redox species combined with oxygen redox could be an interesting approach to further increase energy density of cathode materials for not only sodium‐based rechargeable batteries, but other alkali‐ion battery systems.

P2-type Fe and Mn-based Na0.67Ni0.15Fe0.35Mn0.3Ti0.2O2 as cathode material with high energy density and structural stability for sodium-ion batteries

P2-type layered cathode materials containing Fe and Mn have attracted much attention due to their elemental abundance, low costs and high reversible capacities, and most related work have focused on attaining cathodes with extremely high reversible capacity. However, the extremely high capacity usually leads to several disadvantages, including extremely wide voltage range, fast capacity fading upon cycling, and inappropriate initial Coulombic efficiency. This work investigates P2-type Na0.67Ni0.15Fe0.35Mn0.5O2 (NFM) and Na0.67Ni0.15Fe0.35Mn0.3Ti0.2O2 (NFMT) as high-energy cathode materials by elevating average operating voltage with Ni2+/Ni4+ and Fe3+/Fe4+ redox couples but limiting (de)sodiation in the voltage of 2.0–4.4 V to obtain an medium reversible capacity. NFMT has high energy density of 471 Wh kg−1 with reversible capacity of 157.2 mAh g−1 and average operating voltage of 3.0 V. NFMT also has an initial Coulombic efficiency of 98.8% and a capacity retention of 85.1% after 50 cycles at 20 mA g−1 (0.1C), better than those of some high-capacity P2-type Fe and Mn-based cathodes, showing great potential for future practical application in the sodium full cells. Ti4+ ion acts as pillar ion in the fully charged NFMT cathode, effectively suppressing thickness reduction of the MO2 slab, volume shrinkage of the cathode, and thus inhibiting P2–O2 phase transition at high voltage, which contribute to the improvement of the structural and cycling stability P-type oxides.

Plum pudding model inspired KVPO4F@3DC as high-voltage and hyperstable cathode for potassium ion batteries

The investigation on the cathode material of potassium ion batteries (PIBs), one of the most promising alternatives to lithium ion batteries, is of great significance. Potassium vanadium fluorophosphate (KVPO4F) with a high working voltage is an appealing cathode candidate for PIBs, while the poor cycling performance and low electronic conductivity dramatically hinder the application. Herein, a plum pudding model inspired three-dimensional amorphous carbon network modified KVPO4F composite (KVPO4F@3DC) is successfully designed in this study to tackle these problems. In the composite, KVPO4F particles are homogeneously wrapped by a layer of amorphous carbon and bridged by cross-linked large area carbon sheets. As the cathode for PIBs, the KVPO4F@3DC composite exhibits a high average operating voltage about 4.10 V with a super-high discharge capacity of 102.96 mAh g−1 at 20 mA g−1. An excellent long cycle stability with a capacity retention of 85.4% over 550 cycles at 500 mA g−1 is achieved. In addition, it maintains 83.6% of its initial capacity at 50 mA g−1 after 100 cycles at 55 °C. The design of KVPO4F@3DC with plum pudding structure provides facilitative electron conductive network and stable electrode/electrode interface for electrode, successfully innovating an ultra-stable and high-performance cathode material for potassium ion batteries.

Spinel-layered Li2MnTiO4+z nanofibers as cathode materials for Li-ion batteries

In this study, we propose composite materials based on the Li–Mn–Ti–O system to develop low cost and environmentally benign cathode materials for Li-ion batteries. Specifically, spinel-layered Li2MnTiO4+z (0.5LiMnTiO4•0.5Li2Mn0·5Ti0·5O3) material is studied with the aim to increase the operating voltage of the cathode. In contrast, to increase the capacity as well as rate capability of the cathode, an electrospinning technique is employed to synthesize uniform nanofibers with diameters of approximately 80 nm and a length of 15 μm. The hetero- and one-dimensional structure of the prepared sample facilitate Li+ transport by shortening the diffusion length for the ions. Consequently, high capacities of 210 (average operating voltage ~3.1 V) and 150 mAh g−1 at C/10 and 1C rates, respectively, are obtained.