Cathodes For Sodium Batteries Research Articles

Mechanism and enhanced performance of low-dose low-valence molybdenum-doped Na3V2(PO4)2F2O cathodes for sodium batteries

Sodium vanadium oxyfluorophosphate Na3V2(PO4)2F2O is an attractive cathode material for sodium ion batteries due to its high crystalline stability, high specific capacity and high discharge potential. Currently, the poor electronic conductivity and low diffusion rate of Na+ severely impede its development and application. In this work, low-dose Mo2+ doping is proposed through first-principle computation to enhance the structure and performance of Na3V2(PO4)2F2O. It is found that low-dose of Mo2+ doping can reduce the band gap and energy barrier for Na + diffusion in Na3V2(PO4)2F2O. However, heavy doping leads to serious Jahn-Teller distortion of the crystal structure. Therefore, low-dose Mo2+ doping, ranging from x = 0 to x = 0.06 in Na3V2-xMox(PO4)2F2O, is designed and experimentally carried out. The best performance with 118.5 mA h g−1 at 0.1C and 60.6 mA h g−1 at 20C is obtained in Na3V1.96Mo0.04(PO4)2F2O when x = 0.04 in comparison with other doping amounts. The specific discharge capacity at 0.5C decreases gradually from 105.4 to 77.9 mA h g−1 after 400 cycles, indicating a capacity retention of 73.9 %. These results demonstrate that low-dose Mo2+ doping is an effective strategy to enhance the electrochemical performance of Na3V2(PO4)2F2O, making it a promising cathode material for sodium batteries.

MXene-rGO aerogel assisted Na3.5MnTi(PO4)3 cathode for high-performance sodium-ion batteries

Sodium superionic conductor (NASICON) structured polyanionic materials have recently attracted great attention for robust crystal structures. However, inherent properties of NASICON presents poor electrical conductivity and low energy density. Herein, non-stoichiometric synthesized strategy is used for acquiring N3.5MTP, effectively suppressing voltage hysteresis. Besides, as-fabricated N3.5MTP grains in-situ grow on MXene-rGO aerogels by sol–gel synthesis approach obtaining N3.5MTP@MXene-rGO. MXene-rGO aerogel as an excellent conductive matrix can effectively avoid agglomeration of Na3.5MnTi(PO4)3 particles and alleviate volume change of the lattice during sodium ion intercalation/deintercalation. Moreover, cross-linked network of N3.5MTP@MXene-rGO provides fast electron transfer and ion transport rates. The above synergistic effect and contribution of pseudocapacitance make it an excellent discharge capacity of 189 mA h g−1 at 50 mA g−1 for N3.5MTP@MXene-rGO, long cycles of 5000 cycles, as well as 98 mA g−1 at −30 °C (50 mA g−1). Prospectively, this study provides an effective strategy for improving electrochemical performance of NASICON-type cathode for sodium batteries.

A unique polymer-inorganic cathode-electrolyte-interphase (CEI) boosts high-performance Na3V2(PO4)2F3 batteries in ether electrolytes

The practical utilization of ether electrolytes has long been restricted due to the concern on its electrochemical oxidation stability. Recently, it has been demonstrated that ethers are compatible with a series of polyanionic cathodes for sodium batteries. However, the specific cathode-electrolyte interface is still poorly understood. In this work, via the use of highly complementary surface and interfacial characterization techniques, we identify that the use of an 1 M NaPF6-diglyme solution allows the formation of a unique polymer-inorganic cathode-electrolyte-interphase (CEI) on high-voltage Na3V2(PO4)2F3 polyanionic cathodes, contributing to excellent cyclability (capacity retention of 96.2% after 300 cycles at 0.5C, 1C = 128 mAh g−1) and outstanding rate capability (124, 120 and 112 mAh g−1, at 5C, 10C and 20C, respectively). The peculiar interfacial chemistry disclosed here may open up new opportunities for building high performance sodium batteries.

Voltage hysteresis loop as a fingerprint of slow kinetics Co2+-to-Co3+ transition in layered NaxCox/2Ti1−x/2O2 cathodes for sodium batteries

The P2- and O3-Na0.67Co0.33Ti0.67O2 cathodes undergo a very slow transformation during charge and discharge in sodium batteries due to a valence and spin-state transition of cobalt cations. As a result, a big potential hysteresis of 2.5–3 V arises.

Physico-Chemical Features of Undoped and Fe/Cu-Doped Na0.67MnO2-Layered Cathodes for Sodium Batteries

Na0.67MnO2 (NMO) stands out among the layered cathode materials used for sodium batteries due to its high-capacity values, low cost, and environmental friendliness. Unfortunately, many drawbacks arise during cycling, but nanostructure tailoring and doping can help to mitigate them. Our aim was to synthesize undoped and Cu- or Fe-doped NMO samples via the sol-gel route, with a different cooling step to room temperature, i.e., in a natural way or via quenching. The formation of a mixture of polymorphs was observed, as well as differences in the external morphology of the powders’ grains. The use of spectroscopic techniques, Mössbauer spectroscopy for the Fe-doped samples and Electron paramagnetic resonance, allowed us to gain insights into the oxidation states of transition metals and to make suggestions about the magnetic ordering, as well as on the possible presence of magnetic impurities. Cyclic voltammetry and galvanostatic cycling results were interpreted on the basis of the spectroscopic data: the introduction of substituents, in general, worsens the capacity values, due to the decrease in the P2 amount and the introduction of structural distortions. The structural stability of the samples in air as a function of time was also analyzed via X-ray diffraction, demonstrating the positive effect of Cu presence.

Utilization of the V5+/V4 + Redox Reaction in Nasicon-Structured Cathode Materials for Sodium-Ion Batteries

The energy problem has become a critical issue worldwide, and renewable energy will dominate the energy system in the near future. Electrochemical storage devices are widely used as the energy storage devices of renewable energy, and the most intuitive feeling is that electric vehicles driven by lithium-ion batteries (LIBs) have become a new generation of transportation. Nevertheless, the worrisome side though was the high cost of LIBs and the scarcity of lithium. Considering that high crustal abundances of sodium and large-scale energy storage devices are almost not restricted by the size of the device, sodium-ion batteries (SIBs) were considered as a promising alternative to the LIBs.1 Cathode materials, as the highest cost proportion of SIBs (32.4 %), have always been the bottleneck of development and high-performance cathode materials are actively being explored by researchers. Sodium super ionic conductor (NASICON)-structured materials, as a member among the most investigated cathode materials for SIBs, are a promising candidate due to the excellent stability of long-term cycling.Na3V2(PO4)3 is the most classical cathode material in NASICON-structures with the high working potential (3.4 V, corresponding to the V4+/V3+ redox reaction) and high specific capacity (117.6 mAh g-1). Recently, many studies have shown that the V5+/V4+ redox reaction can be accessed through partial substitution of V3+.2 However, two phenomena needed deep consideration: (1) the potential of the V5+/V4+ redox reaction in Na3V2(PO4)3 is different from its derivatives, and (2) the utilization of the V5+/V4+ redox reaction is very limited. In one of our work, Na3VAl(PO4)3 and Na3VGa(PO4)3 cathode materials were selected as contrasting systems to explain these two phenomena because Al and Ga are in the same group. Combining experimental tests and density functional theory (DFT) calculations, sodium ions are extracted/inserted from/into different sodium sites, causing a different potential of the V5+/V4+ redox reaction; and the full use of the V5+/V4+ redox reaction was restricted by the excessive diffusion energy barrier.3 Therefore, we proposed two possible approaches to promote the V5+/V4+ redox reaction: (1) substitution of V3+ with smaller ions and (2) utilizing the x = 2.0-3.0 region.As described previously, the access of V5+/V4+ redox reaction is difficult. Reducing the amount of substitution is an effective method to fully use of the V5+/V4+ redox reaction. We have studied successively the electrochemical properties of Na3V1+x Cr1-x (PO4)3 (x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5),4 Na3V1+x Al1-x (PO4)3 (x = 0.3, 0.5 and 0.7) and Na3V1+x Ga1-x (PO4)3 (x = 0.5 and 0.8). To sum up, Na3V1.7Al0.3(PO4)3 has a good trade-off in utilization of the V5+/V4+ redox reaction and the V4+/V3+ redox reaction. The reversible specific capacity of Na3V1.7Al0.3(PO4)3 is 105.8 mAh g-1 in the first cycle and the specific capacity retention is 95.6 % after 50 cycles at 20 mA g-1.References Goikolea, E.; Palomares, V.; Wang, S.; Larramendi, I. R.; Guo, X.; Wang, G.; Rojo, T., Na‐Ion Batteries—Approaching Old and New Challenges. Advanced Energy Materials 2020, 10 (44), 2002055. Gao, H.; Seymour, I. D.; Xin, S.; Xue, L.; Henkelman, G.; Goodenough, J. B., Na3MnZr(PO4)3: A High-Voltage Cathode for Sodium Batteries. J. Am. Chem. Soc. 2018, 140 (51), 18192-18199. Wang, Q.; Gao, H.; Li, J.; Liu, G. B.; Jin, H., Importance of Crystallographic Sites on Sodium-Ion Extraction from NASICON-Structured Cathodes for Sodium-Ion Batteries. ACS Appl Mater Interfaces 2021, 13 (12), 14312-14320. Wang, Q.; Zhao, Y.; Gao, J.; Geng, H.; Li, J.; Jin, H., Triggering the Reversible Reaction of V3+/V4+/V5+ in Na3V2(PO4)3 by Cr3+ Substitution. ACS Appl Mater Interfaces 2020, 12 (45), 50315-50323. Figure 1

Anionic redox reaction triggered by trivalent Al3+ in P3-Na0.65Mn0.5Al0.5O2.

P3-Na0.65Mn0.5Al0.5O2 (NMAO) has been synthesized and studied as a cathode for sodium batteries, and shows anionic redox reaction (ARR) and exhibits a first charging capacity of ∼110 mA h g-1. The electrochemical mechanism of NMAO was comprehensively investigated by X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and density functional theory (DFT) calculations. The reversible oxygen redox behaviour is triggered by Al3+ through oxygen quasi non-bonding states generated by the relatively ionic interaction of Al and O. Furthermore, the presence of Al3+ can suppress oxygen loss in ARR. This work provides new insights into the design and mechanism of anionic redox active cathode materials.

Sodium Rhodizonate as Cathode Material for Sodium-Ion Batteries

Commercial sodium rhodizonate (Na2C6O6) has been investigated as a cathode material for sodium-ion batteries without additional processing. It has been shown by scanning electron microscopy that the sodium rhodizonate powder consists of particles in the form of octahedra and rods in the size range from hundreds of nanometers to several tens of micrometers. The specific characteristics of Na2C6O6 cathodes have been determined by a galvanostatic cycling method. Their magnitude, as well as stability during multiple charge/discharge cycling has been found to depend on the composition of the electrolyte and a positive electrode manufacturing method. A conclusion has been drawn that this material is prospective for making cathodes for sodium batteries after its further modification, the selection of the optimal cathode manufacturing technology, electrolyte composition, and corresponding cycling conditions.

Perylene derivatives for solar cells and energy harvesting: a review of materials, challenges and advances

Herein, we present a review about recent advances in perylene diimide derivatives applied to organic solar cells and energy harvesting. Several organic and inorganic compounds, most of which are solution processed or thermally evaporated, are used for this purpose. Features such as energy level in relation to the donor material’s thermal and mechanical stability and processability are among the aspects that reflect the performance of these materials as electron acceptors or electrodes. Moreover, the donor/acceptor interface directly reflects the photovoltaic response. Therefore, device engineering efforts have been exerted to achieve proper acceptor distribution along the bulk of thin films or improve the compatibility at the donor/acceptor interface. This review is divided into subsections concerning the use of PDI molecules, PDI dimers/trimers/tetramers, bilayer devices, routes to improve the donor/acceptor interface, PDI-based polymers and energy harvesting. The reports show that PDI derivatives are suitable candidates for replacing fullerene derivatives in OSCs with reduced production cost and improved stability. Moreover, new PDI composites with graphene are promising cathodes for sodium batteries. Therefore, PDI derivatives are low cost and multifunctional materials employed to produce optoelectronic devices with numerous purposes.

Na3MnZr(PO4)3: A High-Voltage Cathode for Sodium Batteries

Sodium batteries have been regarded as promising candidates for large-scale energy storage application, provided cathode hosts with high energy density and long cycle life can be found. Herein, we report NASICON-structured Na3MnZr(PO4)3 as a cathode for sodium batteries that exhibits an electrochemical performance superior to those of other manganese phosphate cathodes reported in the literature. Both the Mn4+/Mn3+ and Mn3+/Mn2+ redox couples are reversibly accessed in Na3MnZr(PO4)3, providing high discharge voltage plateaus at 4.0 and 3.5 V, respectively. A high discharge capacity of 105 mAh g-1 was obtained from Na3MnZr(PO4)3 with a small variation of lattice parameters and a small volume change on extraction of two Na+ ions per formula unit. Moreover, Na3MnZr(PO4)3 exhibits an excellent cycling stability, retaining 91% of the initial capacity after 500 charge/discharge cycles at 0.5 C rate. On the basis of structural analysis and density functional theory calculations, we have proposed a detailed desodiation pathway from Na3MnZr(PO4)3 where Mn and Zr are disordered within the structure. We further show that the cooperative Jahn-Teller distortion of Mn3+ is suppressed in the cathode and that Na2MnZr(PO4)3 is a stable phase.

PVP-modulated synthesis of NaV6O15 nanorods as cathode materials for high-capacity sodium-ion batteries

Highly uniform NaV6O15 nanorods were obtained via a facile and low-cost PVP-modulated hydrothermal process. It is largely accepted that such a unique feature is favorable for rapid diffusion for sodium ions according to the intrinsic crystal structure. As the cathode, the as-prepared NaV6O15 nanorods are capable of delivering a high initial capacity of approximately 157 mA h g−1 at 20 mA g−1 for potentials ranging from 1.5 to 3.8 V and yielding 121 mA h g−1 at a high current density of 200 mA g−1. EIS analysis results demonstrated that the diffusion coefficients DNa as high as 2.71 × 10−12 cm2 s−1 at room temperature. In addition, it could be clearly observed that the NaV6O15 exhibited metallic behavior from the electron density of states, providing excellent electron conductivity. All these results suggest that NaV6O15 nanorods can be a very promising cathode for sodium batteries.

Poly(diphenylaminesulfonic acid sodium) as a cation-exchanging organic cathode for sodium batteries

A Na-rich poly(diphenylaminesulfonic acid sodium) (PDS) is prepared by oxidative polymerization and tested as an organic Na-host cathode for Na-ion batteries. Due to the highly self-doped benzenesulfonic anions grafted on the polyaniline backbones, this redox-active polymer demonstrates a reversible capacity of 100mAhg−1 at an average potential of ~3.4V, reaching its theoretical value of reversible 1 Na insertion/extraction reaction. In addition, this polymer cathode also exhibits considerable rate capability and cycling stability, possibly serving as a low cost and sustainable cathode of Na-ion batteries for widespread electric storage applications.

Olivine Type NaFePO4 Prepared By Electrochemical Delithiation for Sodium Ion Batteries

Nowadays, sodium batteries attracted great interest due to the low cost and the environmental abundance of the sodium. Layered sodium-transition metal oxides, i.e. NaMO2, have been widely investigated as cathode materials for these batteries [1]. However, although Dahn’s group showed the high thermal stability for NaCrO2recently, the results so far obtained are not encouraging since this cathode material suffers of poor cycle life and low thermal stability [2].Metal-phosphate based electrodes, such as Nasicon type Na3V2(PO4)3 and NaFePO4, are believed to be very promising alternative cathodes for sodium batteries [3]. Considerable attention has been addressed to maricite NaFePO4, a phase characterized by the presence of (PO4 3-) tetrahedra that totally surround the Na+ cations, namely a structure with no free channels for Na+ diffusion and accordingly with a poor electrochemical behavior in sodium cells [4]. The NaFePO4 phase with an olivine structure is expected to have better electrochemical properties, as suggested by recent studies conducted on chemically delithiated olivine LiFePO4 [5,6]. The results reported in the quoted references showed in fact that FePO4 heterosite can be obtained by a chemical Li-Na exchange process; the formed NaFePO4, however, could not be cycled due to severe decays in capacity presumably associated with the presence of residual Li in its crystal structure, as speculated by Zaghib’s group.In this work we show that, by adopting a refined, electrochemical process, the LiFePO4 can be successfully and efficiently totally converted in NaFePO4and demonstrate that this material can be used as cathode in a sodium battery having excellent performance in terms of cycle life and rate capability.The process of transformation of olivine LiFePO4 to FePO4 was conducted electrochemically with conditions such as to assure a full delithiation of LiFePO4 and its total exchange in FePO4 (see experimental section for details). Figure 1A shows the voltage profile of this first process, evolving on the expect 3.5V plateau and delivering a capacity almost matching the theoretical value [7], both evidences demonstrating that the transformation of LiFePO4 into FePO4 was indeed almost completed. The achievement of the reaction process is confirmed by the XRD analysis, Figure 1B black and red patterns (LiFePO4 peaks were neglibable), demonstrating that the olivine LiFePO4 phase (triphylite) is fully delithiated to form the olivine FePO4(heterosite, JCPDS card No. 42-0579, Pnma space group) phase.

Electrochemical Performances of NaFePO4 Prepared By Electrochemical Delithiation for Sodium Batteries

Introduction Nowadays, sodium batteries attracted great interest due to the low cost and the environmental abundance of the sodium. Layered sodium-transition metal oxides, i.e. NaMO2, have been widely investigated as cathode materials for these batteries [1]. However, although Dahn’s group showed the high thermal stability for NaCrO2recently, the results so far obtained are not encouraging since this cathode material suffers of poor cycle life and low thermal stability [2].Metal-phosphate based electrodes, such as Nasicon type Na3V2(PO4)3 and NaFePO4, are believed to be very promising alternative cathodes for sodium batteries [3]. Considerable attention has been addressed to maricite NaFePO4, a phase characterized by the presence of (PO4 3-) tetrahedra that totally surround the Na+ cations, namely a structure with no free channels for Na+ diffusion and accordingly with a poor electrochemical behavior in sodium cells [4]. The NaFePO4 phase with an olivine structure is expected to have better electrochemical properties, as suggested by recent studies conducted on chemically delithiated olivine LiFePO4 [5,6]. The results reported in the quoted references showed in fact that FePO4 heterosite can be obtained by a chemical Li-Na exchange process; the formed NaFePO4, however, could not be cycled due to severe decays in capacity presumably associated with the presence of residual Li in its crystal structure, as speculated by Zaghib’s group.In this work we show that, by adopting a refined, electrochemical process, the LiFePO4 can be successfully and efficiently totally converted in NaFePO4and demonstrate that this material can be used as cathode in a sodium battery having excellent performance in terms of cycle life and rate capability. Results and discussion The process of transformation of olivine LiFePO4 to FePO4 was conducted electrochemically with conditions such as to assure a full delithiation of LiFePO4 and its total exchange in FePO4 (see experimental section for details). Figure 1A shows the voltage profile of this first process, evolving on the expect 3.5V plateau and delivering a capacity almost matching the theoretical value [7], both evidences demonstrating that the transformation of LiFePO4 into FePO4 was indeed almost completed. The achievement of the reaction process is confirmed by the XRD analysis, Figure 1B black and red patterns (LiFePO4 peaks were neglibable), demonstrating that the olivine LiFePO4 phase (triphylite) is fully delithiated to form the olivine FePO4(heterosite, JCPDS card No. 42-0579, Pnma space group) phase.

ChemInform Abstract: Rechargeable Sodium Batteries. Part 6. Cycling Behavior of VS2, ′VCl3 + nS′ and NbS2Cl2 Cathodes in Molten NaAlCl4.

AbstractThe electrochemistry of V82, ′VC13 + nS′ and NbS2Cl2 has been investigated in relation to their usefulness as Cathodes for sodium batteries operating in the temp. range 160‐200°C. VS; reacts with NaAlCl4 during early stages of cell Cycling, and becomes VS2Cl showing a reversible capacity of z 2.8 electrons/vanadium.