Positive Electrode For Sodium-ion Batteries Research Articles

Influence of Interlayer Cation Ordering on Na Transport in P2-Type Na0.67-xLiy Ni0.33-zMn0.67+zO2 for Sodium-Ion Batteries.

P2-type Na2/3Ni1/3Mn2/3O2 (PNNMO) has been extensively studied because of its desirable electrochemical properties as a positive electrode for sodium-ion batteries. PNNMO exhibits intralayer transition-metal ordering of Ni and Mn and intralayer Na+/vacancy ordering. The Na+/vacancy ordering is often considered a major impediment to fast Na+ transport and can be affected by transition-metal ordering. We show by neutron/X-ray diffraction and density functional theory (DFT) calculations that Li doping (Na2/3Li0.05Ni1/3Mn2/3O2, LFN5) promotes ABC-type interplanar Ni/Mn ordering without disrupting the Na+/vacancy ordering and creates low-energy Li-Mn-coordinated diffusion pathways. A structure model is developed to quantitatively identify both the intralayer cation mixing and interlayer cationic stacking fault densities. Quasielastic neutron scattering reveals that the Na+ diffusivity in LFN5 is enhanced by an order of magnitude over PNNMO, increasing its capacity at a high current. Na2/3Ni1/4Mn3/4O2 (NM13) lacks Na+/vacancy ordering but has diffusivity comparable to that of LFN5. However, NM13 has the smallest capacity at a high current. The high site energy of Mn-Mn-coordinated Na compared to that of Ni-Mn and higher density of Mn-Mn-coordinated Na+ sites in NM13 disrupts the connectivity of low-energy Ni-Mn-coordinated diffusion pathways. These results suggest that the interlayer ordering can be tuned through the control of composition, which has an equal or greater impact on Na+ diffusion than the Na+/vacancy ordering.

Intrinsic Defect and Deformation on Local Structure Caused by Rare‐Earth Ions in the Na3V2(PO4)2F3 Cathode Material

Na3V2(PO4)2F3 has been attracting a lot of attention as a positive electrode material for sodium‐ion batteries (SIBs). The deformation of local structure caused by rare‐earth ions and intrinsic defect properties in Na3V2(PO4)2F3 as a positive electrode for SIB have been investigated with atomistic simulation based on the lattice energy minimization. A good reproduction of the Na3V2(PO4)2F3 structure is obtained. It is revealed that Na Frenkel defect, which is formed by sodium interstitial and vacancy pair, is the most favorable type of intrinsic defect. This leads to the formation of stable sodium vacancy required for the Na‐ion diffusion. The results indicate that trivalent rare‐earth dopants at the V3+ site are the most energetically favorable dopants for Na3V2(PO4)2F3, and that the incorporation at the Na and P site could be used as a strategy to increase the sodium vacancy and interstitial, respectively. The deformation in the local structure by the rare‐earth ions doping at the V site is also investigated as helpful in improving the rate performance of SIBs.

On the synthesis and potential benefit of Na-rich P-type layered oxides for high power Na-ion batteries

Layered oxides with the general composition NaxMO2 (M = transition metal) have attracted a lot of attention for their composition diversity and promising electrochemical performances as positive electrode for sodium-ion batteries. P-type compositions offer power capabilities owing to the fast diffusion of sodium cations but are plagued by limited specific capacities because of the nominal low amount of sodium in the structure. Therefore, sodium enriching of P-type structure is consequently of interest to propose electrode candidates combining high energy density and high power capabilities.Herein co-precipitation syntheses of sodium-rich P-type NaxMn2/3Ni1/3O2 and NaxMn1/2Ni1/2O2 have been attempted and the synthesis mechanism carefully monitored by X-rays diffraction follow up in temperature. The optimization of the synthesis protocol led to stabilize only P3-type single-phases. The combination of several characterization techniques shows that the actual Na content is limited to x = 0.8 far from targeted stoichiometry but still higher than conventionally reported for most of P3-type layered oxides.The investigation of the electrochemical behavior of Na-rich P3-type compounds shows that they behave similarly to stable P2-type and O3-type homologue used as reference.Consequently, efficiency of highly sodiated P3-type layered oxides as a way to combine high energy density and power capabilities is questioned while the interest in stabilizing Na-rich P2-type remains an open question.

Delithiation of LiFePO4 with Cl2 Gas: Preparation of FePO4 for Sodium-Ion Batteries with High Li Recovery

Triphylite NaFePO4 is considered a promising positive electrode for sodium-ion batteries due to its exclusive composition of abundant elements, high thermal stability, and theoretical capacity (154 mAh g–1). However, the low thermodynamic stability of triphylite NaFePO4 precludes direct synthesis techniques such as the solid-state route, thus hampering its commercial viability. Herein, we report a novel preparation of heterosite FePO4, a triphylite NaFePO4 desodiation product, through the delithiation of triphylite (olivine) LiFePO4 using Cl2 gas. In addition to the scalability prospects, the present technique efficiently recovers the lithium source in a utilitarian form. The prepared FePO4 electrode yields a high reversible capacity of 127 mAh (g-FePO4)−1 at 0.05C (1C = 154 mA g–1) and good cycling performance (capacity retention of 98.5% after 250 cycles at 1C). X-ray diffraction revealed the reversible phase transition between heterosite FePO4 and triphylite NaFePO4 during charge–discharge.

Optimized synthesis of Na2/3Ni1/3Mn2/3O2 as cathode for sodium-ion batteries by rapid microwave calcination

Microwave calcination is proposed as an alternative route to conventional heating to prepare layered P2–Na2/3Ni1/3Mn2/3O2 as a positive electrode for sodium-ion batteries. The sample obtained by the fastest conditions, with a heating ramp of 20 °C min−1 for only 2 h, showed well-crystallized rounded particles. Cyclic voltammetry and impedance spectroscopy evidenced a low internal cell resistance, and high diffusion coefficients, which justify its capability to sustain the highest capacity at 1 C and retain the discharge capacity for at least two hundred cycles.

NaxMnyNi1-YO2 Cathode Materials for Sodium-Ion Batteries: Structure, Synthesis, Electrochemistry and Influence of Ambient Storage

Expanding energy generation from renewables is inevitable to reduce the impact of man-made climate change. With that, the need for intermediate energy storage is gaining in significance. Today, lithium-ion batteries (LIBs) are dominating mobile drive-trains and also play a key role in stationary energy storage. LIBs are incorporating critical raw materials in view of availability and economic importance, such as cobalt, lithium, copper and graphite.Sodium-based batteries, in which sodium replaces lithium as ionic charge-carrier, utilize the same working principles but substitute critical raw materials for abundant and cost-effective alternatives. Hard carbon replaces graphite as anode active material, copper foils are substituted by aluminum current collectors and manganese-based cobalt-free layered host lattices offer promising performance as cathode active material 1,2. By applying established production processes, investment costs are reduced and a rapid scale-up is enabled (Drop-In technology) 3, making SIBs a sustainable, efficient and cost-effective complementary technology to LIBs 4.Among various known cathode active materials for SIBs, the family of layered sodium transition metal oxides (NaxMO2, 1>x>0) offers promising electrochemical performance 2,5–7. These compounds show a wide structural variety (O3, P3, P2) due to the ionic radius of sodium and the tendency for Na+/vacancy ordering 8.The scope of our presentation will be low-cost manganese-based, cobalt-free layered NaxMnyNi1-yO2 cathode active materials for SIBs. We will discuss the influence of the transition metal stoichiometry y on the structure based on Neutron and X-ray diffraction experiments. Using advanced electrochemical methods and diffraction experiments, these structural models are then correlated with physical and electrochemical properties such as Na+/vacancy orderings, solid diffusion coefficients and potential profiles. For y = 3/4, a synthesis phase diagram will be presented covering a broad range of sodium content x and calcination temperature. For phase-pure P2-NaxMn3/4Ni1/4O2, we will present the influence of the calcination process on the structure and discuss the electrochemical properties in half-cells in-depth. For optimized materials, attractive initial specific discharge capacities beyond 220 mAh g-1 are obtained in sodium half-cells between 1.5 – 4.3 V. A capacity decay occurs during electrochemical cycling within this full voltage window. The origin of the capacity decay will be discussed based on electrochemical studies and ex-situ investigations of the morphology with SEM and local structure with HRTEM. Finally, we will present the influence of storage in ambient air to gain insights on the large-scale processability of the materials.The chosen synthesis route adapts industrially established processes for NCM production for SIB cathode materials, enables to tune powder properties to technical specifications and is highly scalable. The broad scope of this work addresses raw material questions, fundamental investigations and industrially relevant production processes.ACKNOWLEDMENTS:The German Federal Ministry of Education and Research (BMBF) supported this work within the project TRANSITION (03XP0186C) and ExcellBattMat (03XP0257A and 03XP0257C).REFERENCES Larcher, D. & Tarascon, J.-M. Towards greener and more sustainable batteries for electrical energy storage. Nature Chem 7, 19–29; 10.1038/nchem.2085 (2015).Hasa, I. et al. Challenges of today for Na-based batteries of the future: From materials to cell metrics. Journal of Power Sources 482, 228872; 10.1016/j.jpowsour.2020.228872 (2021).Tarascon, J.-M. Na-ion versus Li-ion Batteries: Complementarity Rather than Competitiveness. Joule 4, 1616–1620; 10.1016/j.joule.2020.06.003 (2020).Vaalma, C., Buchholz, D., Weil, M. & Passerini, S. A cost and resource analysis of sodium-ion batteries. Nat Rev Mater 3, 1–11; 10.1038/natrevmats.2018.13 (2018).Nagore Ortiz-Vitoriano, Nicholas E. Drewett, Elena Gonzalo & Teófilo Rojo. High performance manganese-based layered oxide cathodes: overcoming the challenges of sodium ion batteries. Energy Environ. Sci. 10, 1051–1074; 10.1039/C7EE00566K (2017).Nuria Tapia-Ruiz et al. 2021 roadmap for sodium-ion batteries. J. Phys. Energy 3, 31503; 10.1088/2515-7655/ac01ef (2021).Gonzalo, E., Zarrabeitia, M., Drewett, N. E., López del Amo, Juan Miguel & Rojo, T. Sodium manganese-rich layered oxides: Potential candidates as positive electrode for Sodium-ion batteries. Energy Storage Materials 34, 682–707; 10.1016/j.ensm.2020.10.010 (2021).Kubota, K., Kumakura, S., Yoda, Y., Kuroki, K. & Komaba, S. Electrochemistry and Solid‐State Chemistry of NaMeO 2 (Me = 3d Transition Metals). Adv. Energy Mater. 8, 1703415; 10.1002/aenm.201703415 (2018).

Effect of Cu substitution on anion redox behaviour in P3-type sodium manganese oxides

Sodium layered oxides which display oxygen anion redox behaviour are considered promising positive electrodes for sodium-ion batteries because they offer increased specific capacities. However, they suffer from irreversible structural changes resulting in significant capacity loss and limited oxygen redox reversibility. Here the effect of Cu substitution on the electrochemical performance of P3-type sodium manganese oxide is examined by evaluating the structural and electronic structural evolution upon cycling, supported by density functional theory (DFT) calculations. Over the voltage range 1.8–3.8 V vs. Na/Na+, where the redox reactions of the transition metal ions contribute entirely towards the charge compensation mechanism, stable cycling performance is maintained, showing a capacity retention of 90% of the initial discharge capacity of 166 mA h g−1 after 40 cycles at 10 mA g−1. Over an extended voltage range of 1.8–4.3 V vs. Na/Na+, oxygen anion redox is invoked, with a voltage hysteresis of 110 mV and a greater initial discharge capacity of 195 mA h g−1 at 10 mA g−1 is reached. Ex-situ powder x-ray diffraction patterns reveal distortion of the P3 structure to P′3 after charge to 4.3 V, and then transformation to O′3 upon discharge to 1.8 V, which contributes towards the capacity fade observed between the voltage range 1.8–4.3 V. DFT with projected density of states calculations reveal a strong covalency between the copper and oxygen atoms which facilitate both the cationic and anionic redox reactions in P3-type Na0.67Mn0.9Cu0.1O2.

Comprehensive Study of Sodium Copper Hexacyanoferrate, as a Sodium-Rich Low-Cost Positive Electrode for Sodium-Ion Batteries

Comprehensive Study of Sodium Copper Hexacyanoferrate, as a Sodium-Rich Low-Cost Positive Electrode for Sodium-Ion Batteries

Binder and conductive diluents free NaVPO4F based free-standing positive electrodes for sodium-ion batteries

Herein, we report a carbon-fiber-based freestanding electrode for NaVPO4F cathodes in sodium-ion batteries. The replacement of conventional aluminium foil with a carbon fiber mat-based current collector results in significant improvement in capacity at high rates and charge-discharge cycle stability. Petroleum-pitch (P-Pitch) has dual functions. P-pitch is used as a binder to bind NaVPO4F particles onto the carbon fiber mat, which helps to eliminate typical organic binders. At the same time, P-Pitch acts as a conducting precursor to coat onto NaVPO4F particles. The amount of P-pitch required to achieve stable electrochemical performance is optimized. As a result, 15 and 20% of P-pitch in the composite NaVPO4F electrodes (15P_NVPF@CF and 20P_NVPF@CF) shows stable electrochemical performances. A reversible capacity of 120 and 119 mAh g−1 is observed for 15P_NVPF@CF and 20P_NVPF@CF, with 97 and 98% retention in capacity after 300 cycles, respectively. Further, at a 0.5 C current rate, 15P_NVPF@CF and 20P_NVPF@CF electrodes show 86 and 87% capacity retention after 1000 cycles. The significant electrochemical performance of these freestanding electrodes is ascribed to the interlinked carbon matrix with NaVPO4F particles and carbon-fiber mat, which provides a continuous path for electronic conduction and faster kinetics of NaVPO4F particles.

Titanium- and niobium-doped fluorophosphates as positive electrodes for sodium-ion batteries

• Description of a new low-temperature synthesis of fluorophosphates. • Titanium doping improves storage capacities of fluorophosphates as positive electrodes do ion-sodium batteries. • Niobium doping increase capacity retention of fluorophosphates as positive electrodes do ion-sodium batteries. Sodium fluorophosphates are among the most promising materials for positive electrodes in sodium-ion batteries; however, their low electronic conductivity, kinetics limitations, and structural instability prevent them from reaching their full potential. We obtained sodium vanadium fluorophosphates (NVPF) doped with Ti 4+ (NVTPF) and Nb 5+ (NVNPF) via an original low-temperature synthesis. It was observed that Ti 4+ doping facilitated access to electrode sites and provided higher capacities at high current densities while Nb 5+ provided a 91.7% capacity retention from the 20th to 200th cycle, which was over the 80.1% capacity retention of NVPF. Moreover, both NVTPF and NVNPF provided diffusion coefficients in the range of ~10 −10 cm 2 s −1 , which was better than ~10 −12 cm 2 s −1 of NVPF. Additionally, electrochemical impedance spectroscopy and ex situ X-ray diffraction measurements confirmed that Ti 4+ enhanced the electrode kinetics and stabilized its structure through sodiation/desodiation reactions. The results presented in this paper might provide insights and new directions to enhance the electrochemical storage properties of fluorophosphates.

Iron substitution in Na4VMn(PO4)3 as a strategy for improving the electrochemical performance of sodium-ion batteries

Six NASICON type samples with Na4-xVFexMn1-x(PO4)3 (0 ≤ x ≤ 1) stoichiometry are examined as positive electrodes for sodium-ion batteries. The structural, morphological, and chemical state of elements in raw samples is unveiled by XRD diffraction, electron microscopy, and Raman and XPS spectroscopies. The effect of the dual Fe/Mn substitution is examined by electrochemical tests using both voltammetric and galvanostatic methods. The results reveal the beneficial effect of the iron substitution, justified by an improvement of the kinetic response, and supported by the calculation of the apparent diffusion coefficients and internal cell resistance.

Effect of the Mn/V ratio to optimize the kinetic properties of Na3+xMnxV1-xCr(PO4)3 positive electrode for sodium-ion batteries

Several samples of the Na3+xMnxV1-xCr(PO4)3 series, in which the Mn/V ratio was allowed to vary from 0 to 1, are structural, chemical, and morphologically characterized using helpful solid-state techniques such as XRD diffraction, electron microscopy, and Raman and XPS spectroscopies. These cathode materials are tested by both galvanostatic and voltammetric methods to unveil their electrochemical response. The intermediate compositions showed a biphasic transition and a combination of the profiles belonging to the end member of the series: V4+/V3+ Mn3+/Mn2+ and Mn 4+/ Mn 3+ redox couples. The correlation of apparent diffusion coefficients and the cell internal resistance allowed us to conclude the beneficial effect of intermediate Mn-V composition (x = 0.4) to optimize the electrochemical performance and kinetic properties in sodium-ion cells.

Electrochemical investigations of high-voltage Na4Ni3(PO4)2P2O7 cathode for sodium-ion batteries

The electrochemical properties of carbon and reduced graphene-coated Na4Ni3(PO4)2P2O7 materials have been evaluated as high-voltage positive electrodes for sodium-ion batteries. Na4Ni3(PO4)2P2O7 exhibits the highest Ni3+/Ni2+ redox potential of 4.8 V vs. Na+/Na with a theoretical capacity of 127 mAh g−1. Here, we report on the synthesis and characterizations of Na4Ni3(PO4)2P2O7-reduced graphene oxide and Na4Ni3(PO4)2P2O7-carbon composites. The high-voltage dimethyl carbonate–based electrolyte has been chosen to explore the electrochemical properties of Na4Ni3(PO4)2P2O7 as a cathode. Carbon-coated Na4Ni3(PO4)2P2O7 composite electrode delivers a stable discharge capacity of 51 mAh g−1 at 0.1 C rate for 40 cycles which corresponds to a reversible intercalation/de-intercalation of 1.3 sodium ions. The structural deformation has been observed during the charge–discharge process beyond the removal of 1.3 Na+ ions and has been confirmed by in situ PXRD measurements. The present results provide a guideline to improve the performances of the high-voltage Na4Ni3(PO4)2P2O7 material for the next generation sodium-ion batteries.

Effect of chromium doping on Na3V2(PO4)2F3@C as promising positive electrode for sodium-ion batteries

Cr-doped Na3V2(PO4)2F3@C samples, obtained by a one-step sol-gel method, are studied as cathode materials for sodium-ion batteries. Their structural and morphological properties induced by Cr incorporation are determined by powerful solid-state techniques including X-ray diffraction, electron microscopy, and Raman and XPS spectroscopies. Galvanostatic tests reveal the beneficial effects of low-level Cr doping in Na3V2(PO4)2F3, mainly improving the kinetic response of the electrode materials at the highest studied rates. These results are correlated to low cell internal resistances and cell polarization between charge and discharge. Eventually, a full sodium-ion cell is essayed as a proof of concept to evidence the reliability of these cathode materials in practical conditions.

Reinvestigation of Na2Fe2(C2O4)3·2H2O: An Iron-Based Positive Electrode for Secondary Batteries

We have reinvestigated the polyanionic compound Na2Fe2(C2O4)3·2H2O, previously reported to be electrochemically inactive in lithium-ion batteries (LIBs), as a positive electrode for sodium-ion batteries (NIBs). The present study demonstrates that it is capable of delivering a reversible capacity close to its theoretical value (117 mA h g–1) with three redox plateaus at 2.9, 3.3, and 3.6 V versus Na/Na+ in the potential range 1.7–4.2 V. The obtained energy density of 326 W h kg–1 is among the highest of all reported polyanionic cathodes in NIBs. The origin of the electrochemical activity can be traced back to the electronic structure of the compound and the low migration energy barrier of the alkali ion observed in first-principles density-functional theory calculations.

VIV Disproportionation Upon Sodium Extraction From Na3V2(PO4)2F3 Observed by Operando X-ray Absorption Spectroscopy and Solid-State NMR

Among the series of polyanionic positive electrodes for sodium-ion batteries having the general formula Na3V2(PO4)2F3–yOy (0 ≤ y ≤ 2), the composition Na3V2(PO4)2F3 (y = 0) has the highest theoretical energy that offers competitive electrochemical performances compared to sodium transition metal oxides. Recently, the structural phase diagram from Na3V2(PO4)2F3 to Na1V2(PO4)2F3 has been thoroughly investigated by operando synchrotron X-ray diffraction revealing an unexpected structural feature for the end member composition. In fact, the crystal structure of Na1V2(PO4)2F3 has two very different vanadium environments within each bioctahedron that suggests a charge disproportionation of two VIV into VIII and VV. This work shows an operando X-ray absorption spectroscopy at vanadium K edge during the electrochemical extraction of Na+ in order to monitor the redox processes involved in this compound. The large data set provided by this experiment has been processed by the principal component analysis combined with multivariate curve resolution. The results suggest that the bioctahedra have to be considered as the basic structural unit. The peculiar geometry of this material combined with the mixed vanadium valence, directly investigated here along the reaction, seems to allow original electronic configurations. In particular, the two vanadium sites into the basic bioctahedra unit evolve from VIII–VIII to VIII–VIV and to a final VIII–VIV configuration. These observations are completed with 51V NMR sensitive to diamagnetic VV.

Cobalt-substituted Na0.44Mn1-xCoxO2: phase evolution and a high capacity positive electrode for sodium-ion batteries

Na0.44Mn1-xCoxO2 (x=0, 0.01, 0.08, 0.11, 0.22, 0.33, 0.44) powders are synthesized as positive electrodes for sodium-ion batteries via a thermopolymerization method. X-ray diffraction and scanning electron microscopy are used to analyze their crystal structures and particle morphologies. Galvanostatic cell cycling is used to characterize the electrochemical properties. The Co-substitution can change the structure of Na0.44Mn1-xCoxO2 from T-type (x=0) into layered P2-type (x=0.11) or P3-type (x=0.44). For the samples synthesized under our specific conditions, the particle morphology can be used as an indicator of their crystal structures: rod-like (T-type), plate-like (P2-type) and granules (P3-type). P2-type Na0.44Mn0.89Co0.11O2 allows more Na+ intercalation into the inter-layer spacing and results in a high discharge capacity with 220mAhg−1 at 12mAg−1 in initial cycle, 180mAhg−1 after 40 cycles in the voltage range of 2.0-4.2V and a good rate performance of 104mAhg−1 at a rate of 600mAg−1 in the voltage range of 2.0-4.0V.

Electrochemical Performance of Chemically and Solid State-Derived Chevrel Phase Mo6T8 (T = S, Se) Positive Electrodes for Sodium-Ion Batteries

Chevrel phases, or CPs (Mo6T8; T = S, Se), can accommodate cations (Li+, Mg2+ etc.) within the Mo6T8 open framework at room temperature due to their unusually high electronic conductivity and ionic mobility and are hence proposed as positive electrodes for secondary batteries. However, cation insertion into Mo6T8 generates strong repulsion between the cation–cation or cation–Mo atoms, leading to partial charge trapping within the Mo6T8 structure. The present work examines CPs as positive electrodes for sodium-ion batteries. In this regard, ternary CPs of CuxMo6S8 and CuxMo6Se8 phase were prepared by solution chemistry and high energy mechanical milling (HEMM) routes, respectively, followed by acid leaching of copper. X-ray diffraction and scanning electron micrographs revealed the formation of 1–1.5 μm size cuboidal Cu1.8Mo6S8 particles, whereas, HEMM of CuSe, MoSe2 and Mo powder followed by heating leads to the formation of Cu2Mo6Se8 phase. Results from cyclic voltammetry and galvanostatic cycling of Na/...

Manganese hexacyanomanganate open framework as a high-capacity positive electrode material for sodium-ion batteries.

Potential applications of sodium-ion batteries in grid-scale energy storage, portable electronics and electric vehicles have revitalized research interest in these batteries. However, the performance of sodium-ion electrode materials has not been competitive with that of lithium-ion electrode materials. Here we present sodium manganese hexacyanomanganate (Na2MnII[MnII(CN)6]), an open-framework crystal structure material, as a viable positive electrode for sodium-ion batteries. We demonstrate a high discharge capacity of 209 mAh g(-1) at C/5 (40 mA g(-1)) and excellent capacity retention at high rates in a propylene carbonate electrolyte. We provide chemical and structural evidence for the unprecedented storage of 50% more sodium cations than previously thought possible during electrochemical cycling. These results represent a step forward in the development of sodium-ion batteries.

Na[Ni0.4Fe0.2Mn0.4−xTix]O2: a cathode of high capacity and superior cyclability for Na-ion batteries

New electrode materials of layered oxides, Na[Ni0.4Fe0.2Mn0.4−xTix]O2, have been synthesized as positive electrodes for sodium-ion batteries. The partial substitution of Mn with Ti increases the lattice spacing without changing the lattice structure. A Na//Na[Ni0.4Fe0.2Mn0.2Ti0.2]O2 cell delivers a reversible capacity of 145 mA h g−1 with excellent long cycling performance.