Room-temperature Sodium-ion Batteries Research Articles

Sodium Halide-Based Solid Electrolyte with High Ionic Conductivity

Sodium-ion batteries (SIBs) are considered one of the most prominent alternatives to lithium-ion batteries (LIBs) because of the abundance of sodium resources on Earth. However, compared to Li, Na has a heavier atomic weight (23 g mol–1 vs. 6.9 g mol–1) and higher standard potential, leading to lower volumetric and gravimetric energy density of SIBs than LIBs. The energy density of state-of-the-art room-temperature SIBs is in the range of 75 – 165 W h kg–1 or 250 – 375 W h L–1. To increase the energy density of SIBs, Na metal is proposed to be used as the anode material due to its superior theoretical specific capacity (1166 mA h g–1). To tackle the safety challenges brought by using Na metal, applying solid electrolytes (SEs) has been proposed to be an effective strategy. Despite the tremendous progress that has been made in the past decades, the progress and application are still in the infancy, experiencing numerous challenges for sodium solid-state batteries due to inherently low room-temperature ionic conductivity, interface complications, and fabrication.Inorganic halide-based SEs have emerged as a game changer because of their fast-conducting characteristics, adequate thermodynamic stability, great deformability, and good oxidative stability.1 Moreover, halide-based SEs are generally stable against moisture owing to their positive hydrolysis reaction energy. However, most of the studied halide-based SEs are based on the Li-ion system, with only a few based on the Na-ion system. Moreover, despite halide-based Na SEs theoretically having high ionic conductivity,2 experimental obtained samples have much lower ionic conductivities compared to their Li counterparts (usually < 0.1 mS cm–1). Therefore, developing halide-based SEs with high Na+ ionic conductivity is crucial for Na ASSBs. We recently identified a new Na halide-based SE with a room temperature Na+ ionic conductivity over 1 mS cm–1. The activation energy is also as low as 0.23 eV. Interestingly, the material shows a mixed amorphous and crystalline phase, and its ionic conductivity decreases with the increase of the crystalline phase. The ionic conductivity of > 1 mS cm–1 is already comparable to some organic liquid electrolytes and thus is sufficient for many practical applications. The developed strategy has the potential to be applied to other halide-based SEs to improve their ionic conductivity, promoting the development of SIBs.(1) Huang, J.; Wu, K.; Xu, G.; Wu, M.; Dou, S.; Wu, C. Recent Progress and Strategic Perspectives of Inorganic Solid Electrolytes: Fundamentals, Modifications, and Applications in Sodium Metal Batteries. Chem. Soc. Rev. 2023, 52 (15), 4933–4995.(2) Qie, Y.; Wang, S.; Fu, S.; Xie, H.; Sun, Q.; Jena, P. Yttrium–Sodium Halides as Promising Solid-State Electrolytes with High Ionic Conductivity and Stability for Na-Ion Batteries. J. Phys. Chem. Lett. 2020, 11 (9), 3376–3383.

New dual-anions FeS0.5Se0.5@NC porous nanorods as advanced electrode materials for wide-temperature sodium-ion half/full batteries

The new N-doped carbon wrapped porous FeS0.5Se0.5 nanorods (FeS0.5Se0.5@NC) have been rationally designed using the FeOOH nanorod as a reaction template, poly-dopamine as the carbon source, combined with the subsequent sulfuration and selenization process. Due to the cooperative effect of dual-anion guided heterostructure, and the effective protection of highly conductive and uniform N-doped carbon layer, the FeS0.5Se0.5@NC as the new anode materials for room-temperature sodium ion batteries demonstrates remarkable sodium storage properties. When the current density is 0.5 A g−1, the FeS0.5Se0.5@NC can deliver a satisfied specific capacity of 522.8 mAh g−1 over 100 loops. Even at 5 A g−1, it still shows outstanding long-period cycling stability (450 mAh g−1 for 220 cycles). It also displays prominent rate capability (242.65 mAh g−1 at 20 A g−1). Even at a low temperature, the FeS0.5Se0.5@NC still shows good sodium storage properties. Except for the half-cells, the full cells also exhibit good electrochemical performances. Furthermore, various kinetic analysis and reaction mechanism of FeS0.5Se0.5@NC are investigated to analyze the excellent sodium storage properties. The synthesis strategy of FeS0.5Se0.5@NC can be adopted to prepare the other kinds of double anionic metal chalcogenides anode materials to explore the potential applications in different energy storage fields.

Carbon-coated sodium vanadium phosphate for high-performance sodium-ion batteries

Room temperature sodium ion batteries are feasible for large energy storage equipment because they are both safe and inexpensive. However, the low electronic conductivity of sodium ion battery cathode material is an inherent flaw. Here, the solid-phase carbothermal reduction method was used to create Na3V2(PO4)3/C composites coated with four different carbon sources (Vc, maltose, sucrose, and PEG-2000). XRD and SEM were used to examine the crystal structure and microstructure; the electrochemical properties of four samples were examined using a constant current charge discharge test and AC impedance spectroscopy. As a result, the samples coated with PEG-2000 were identified to have an excellent microstructure and good electrochemical properties. Specifically, the discharge capacity decays from 103.9 mAh/g to 93.4 mAh/g after 340 cycles, and the corresponding capacity retention rate is 89.89%. Moreover, the outstanding electrochemical performance of Na3V2(PO4)3/C composites demonstrates that it is a promising material for the practical application of sodium-ion batteries.

Synchronous crystal growth and etching optimization of Prussian blue from a single iron-source as high-rate cathode for sodium-ion batteries

Prussian blue (PB) and its analogues (PBAs) have been considered as promising cathodes for room temperature sodium-ion batteries (SIBs) because of their rigid open framework and low-cost synthesis. Herein, we have synthesized slight-etching PB cubes with low amounts of coordinated water and [Fe(CN)6] vacancies using an optimized hydrothermal method with the aid of acid. Interestingly, synchronous crystal growth and etching processes are observed, accompanied by recrystallization behaviors during the etching process. With the increasing acid amount, yield of the as-prepared PB improves greatly. The acid etching mechanism is further clarified. Notably, such one-step acid-etching hydrothermal approach can realize the rational composition and architecture design of PB. The correlation between physical properties and cell performance of PB is systematically investigated. The optimized PB cubes with slight surface etching deliver a high reversible specific capacity of 99 mA h g−1, a capacity retention of 79% for 500 cycles and 74 mA h g−1 at a high current density of 1500 mA g−1. Such superior rate capability and long cycle life are ascribed to the synergistic effects of the structure and morphology of PB, which possesses low amounts of coordinated water and [Fe(CN)6] vacancies, large unit cell volume, and slight-etching surface in the cubic structure, good crystallinity and uniform particle size distribution.

Quasi-1D TiS3: A potential anode for high-performance sodium-ion storage

Owing to the natural abundance of sodium and the low cost of sodium resources, room temperature sodium-ion batteries are considered as attractive candidates for the next generation rechargeable batteries. To explore excellent anode materials for sodium-ion batteries, here we report TiS3 with quasi-1D structure as a potential electrode material. TiS3 micro-belts are successfully prepared via a facile solid-state reaction and demonstrated to be a desirable anode material. When applied in sodium-ion batteries, the TiS3 delivers a high reversible capacity of 346.3 mAh g−1 at 2 A g−1 after 500 cycles and excellent rate capability of 192.5 mAh g−1 at 10 A g−1. The impressive sodium storage behavior can be attributed to the amorphization process during sodiation, the surface-controlled pseudocapacitive behavior as well as the low charge transfer resistance. The unique behavior of TiS3 could provide new insights on the design of transition metal trichalcogenides as promising anode materials for sodium storage.

Improving electrochemical performance of Na3(VPO4)2O2F cathode materials for sodium ion batteries by constructing conductive scaffold

Room-temperature sodium ion batteries (SIBs) are considered as a potential candidate to substitute the high-cost lithium ion batteries due to the high abundance of sodium resources; however, it is still a challenge to develop high power/energy density and stable cathode materials for SIBs. Recently, Na3(VPO4)2O2F (NVPOF) expresses strong competitiveness under high working voltage in sodium storage field because of its eximious structural stability and high energy density. Nevertheless, the intrinsically poor electronic conductivity hinders its electrochemical performance. Herein, 1 D carbon nanotube (CNT) and 2 D polyaniline (PANI) are utilized as self-templates to prepare NVPOF@CNT/PANI polyhedrons via a facile and cost-efficient synthetic route. The highly conductive CNT/PANI scaffold can offer a quick electron transfer pathway. Benefiting from this unique design, NVPOF@CNT/PANI shows excellent electrochemical performance：delivering a high specific capacity of 125.3 mAh g−1 at 0.5 C, excellent rate property of 62.7 mAh g−1 at 20 C, and long lifespan of 2000 cycles with the capacity of 44.1 mAh g−1 at 10 C. This work for NVPOF gives a promising method to prepare the high-performance cathode material for sodium-ion battery, and this approach can also extend to optimize other battery materials.

In Situ Electrochemical Coating Mechanism of NASICON-Structured AgTi2(PO4)3 for Sodium-Ion Batteries

The development of high-performance electrode materials is of great significance for the next-generation room-temperature sodium-ion batteries. In this work, a new Na super-ionic conductor (NASICON) negative electrode, AgTi2(PO4)3, is prepared by a facile solid-state reaction and employed as a sodium storage material for the first time. In situ X-ray diffraction during battery operation reveals an electrochemically Ag nanoparticle coating mechanism upon sodiation, facilitating the electron transfer in the complex. In addition, two steps of highly reversible biphasic transformation are observed. As a result, a reversible capacity of 214.9 mA h g-1 can be achieved, corresponding to the insertion/extraction of nearly four sodium ions. The AgTi2(PO4)3 electrode also demonstrates better kinetic properties than the bare NaTi2(PO4)3 material. Such an "in situ" decorating method can open up a new direction for the design of NASICON-structured materials.

Understanding the effect of structural compositions on electrochemical properties of titanium-based polyanionic compounds for superior sodium storage

Titanium-based polyanionic compounds have gained wide attentions as anode materials for room-temperature sodium-ion batteries due to the robust structural framework, reversible redox chemistry, and compositional diversities. However, the effect of chemically-inserted cations on their structural and electrochemical properties is lack of being investigated to date. In this work, structural and electrochemical properties of ATi2(PO4)3/C (A = Li, Na, Mg) compounds are comparatively studied by coupling X-ray diffraction, scanning electron microscope, cyclic voltammetry and galvanostatic measurements. Experimental results reveal that the structural composition is an important factor determining electrochemical properties of titanium-based polyanionic compounds, and the Li-containing composition shows the best charge/discharge performance with high specific capacities of 120.4 mAh g−1 at 20 mA g−1 and 89.7 mAh g−1 at 1000 mA g−1, and outstanding cycling stability without capacity fading after 1000 cycles. In particular, full battery assembled with it and Na3V2(PO4)3 cathode can deliver a specific energy of 124.5 Wh kg−1 at the power of 114.9 W kg−1, and a capacity retention of 84.9% after 100 cycles.

Exploring the use of EMImFSI ionic liquid as additive or co-solvent for room temperature sodium ion battery electrolytes

Sodium ion batteries (SIB) market is limited by their gravimetric and volumetric energies and therefore, search of high voltage redox couples combined with suitable electrolytes is nowadays mandatory. Ionic liquids can bring advantageous properties to SIB, particularly from a safe point of view, but are still quite expensive. In this pioneering work, we explore the use of small amounts of 1-ethyl-3-methylimidazolium bis(fluoromethanesulfonyl)imide (EMImFSI) ionic liquid in the electrolyte formulation, either as an additive (2% in weight ratio to a binary mixture of ethylene carbonate (EC)/propylene carbonate (PC)) or as co-solvent (10% in weight ratio). Results are compared to electrolytes containing classical SIB additive fluoro-ethylenecarbonate (FEC). Physicochemical properties of the electrolytes prepared with NaClO4, NaPF6 and NaFSI are differently influenced by the EMImFSI additive, which contributes with ionic species to the electrolyte ionic conductivity but increases its viscosity. Extension of the sodium plating/stripping is higher for more dissociated salt in un-doped electrolytes. Introduction of EMImFSI results in the occurrence of a SEI that hinders the plating except for the 10% EMImFSI-NaFSI based electrolyte. Electrochemical cycling of a hard carbon electrode reveals that FSI− anion, mainly coming from the added ionic liquid, can introduce new peaks in the cyclic voltammetry or new steps in the galvanostatic discharge. The products of such degradation create an electrode/electrolyte interface which determines the cycling properties. The complex picture of the interplay between sodium salt anion and EMImFSI presence and amount is not completely described in this work. However, it is clear that EMImFSI introduces initially a larger polarization in the discharge/charge curves and that only added to the NaPF6 system helps to stabilize the coulombic efficiency and gain in capacity (+50%). EMImFSI has not beneficial effect on the NaClO4-based formulations and the initial positive effect on the sodium half cells cycled in NaFSI-based electrolytes is cancelled after 25 cycles. Microscopy examinations on cycled electrodes reveal that coulombic efficiency and thus capacity retention are associated to a protective film completely recovering the hard carbon particles without modifying their pristine shape. This is the case for electrodes tested with un-doped NaClO4 and EMImFSI-NaPF6 electrolytes. Our results also show that compared with EMImFSI, FEC added in 2% weight ratio content provides much better or similar electrochemical performances at a lower price.

Sodium storage property and mechanism of NaCr1/4Fe1/4Ni1/4Ti1/4O2 cathode at various cut-off voltages

Room-temperature sodium-ion batteries (SIBs) have attracted extensive interest in large-scale energy storage applications for renewable energy and smart grid, owing to abundant sodium resources and low cost. O3-layered sodium transition metal oxides (i.e., NaMO2, M = Ti, V, Cr, Mn, Fe, Co, Ni, Cu, etc.) are considered as a promising class of cathode materials for SIBs due to their high capacity and ease of synthesis. In this work, a quaternary layered material O3–NaCr1/4Fe1/4Ni1/4Ti1/4O2 (O3-NCFNT) is successfully synthesized and investigated as a new cathode material for SIBs. Within the voltage range of 1.5–4.1 V, O3-NCFNT delivers an ultrahigh charge capacity of 213 mA h g−1 but a limited discharge capacity of 107 mA h g−1 in the initial cycle. Ex situ X-ray diffraction and X-ray absorption spectroscopy results reveal that an irreversible phase transformation as well as the irreversible redox of Cr3+/Cr6+ within the voltage range of 1.5–4.1 V should be responsible for the capacity decay in the initial cycle. While, O3-NCFNT exhibits the initial charge/discharge capacities of 135.4 and 129.2 mA h g−1 with a high coulombic efficiency of 95.4% as well as good cyclic performance within the voltage range of 1.5–3.4 V at current rate of 0.1C. Especially, O3-NCFNT shows a capacity retention of 77.1% after 300 cycles at a high rate of 1C, indicating that the structural origins of capacity decay caused by excessive sodium extraction are confirmed by XRD and XAS measurements to unlock the potential of this material for sodium-ion battery application.

Transport Limitations of Sodium-Ions in Type-II Clathrates

The development of material for room temperature sodium ion batteries with high cycling stability is of great significance. Clathrates are potential sodium ion conductors with the properties of cage-like frameworks. It is predicted that the open cages can easily accommodate alkali ions with negligible volume changes. In this paper, we evaluated the type II clathrate performance in sodium ion batteries. Slightly elevated testing temperature (45 oC) can improve the cell capacity and rate performance due to the improved ionic conductivity. Side reactions on the solid electrolyte interface and loss of active materials during the first sodiation process contribute to the low Coulombic efficiency of the first cycle. Electrode morphology and elemental mapping analysis for clathrate electrodes at different states corroborate the above analysis.

Nitrate Combustion Synthesis of NVP-Type Cathode Material for Na-Ion Batteries

The synthesis and characterization of a Na3V2(PO4)3 cathode material for room-temperature sodium-ion battery is reported. The NVP material was prepared using a two-step process which proceeded via sol-gel nitrate combustion method for precursor preparation and subsequent pyrolysis under Argon. The materials have been investigated using SEM, EDX, XRD and TOF-SIMS methods. Electrochemical characterization has been carried out using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge/discharge method (GCD). The electrode slurry was prepared by mixing the active material, conductive additive (Super P) and polyvinylidene difluoride (PVdF) binder in a 75:15:10 mass ratio. The mixed slurry was cast onto aluminium foil using doctor-blade technique. The cast electrodes were dried under vacuum for 24h. Electrochemical tests were carried out in coin cells, which were assembled in an Argon-filled glovebox (O2 < 0.1 ppm, H2O < 0.1 ppm). Sodium metal was used as the counter electrode and 1M NaPF6 in EC:PC (1:1 vol) as the electrolyte in half-cell measurements. Acknowledgements The present study was supported by European Regional Development Fund (Centres of Excellence TK141 (2014-2020.4.01.15-0011)6, Higher education specialization stipends in smart specialization growth areas 2014-2020.4.02.16-0026), “Institutional development program for research and development and higher education institutions” (ASTRA) (Graduate School of Functional Materials and Technologies, Materials Technology Projects SLOKT12180T and SLOKT12181T, Energy Technology Project SLOKT10209T), Estonian Research Council (Institutional Research Grant IUT20–13 and by NAMUR project 3.2.0304.12-0397. Mr. Väli thanks Estonian Students Fund in USA for financial support.

Na2 + 2xFe2-x (SO4)3@rice husks carbon composite as a high-performance cathode material for sodium-ion batteries

Na2 + 2xFe2-x (SO4)3 (NFS) holds great promise as the cathode material for room-temperature sodium-ion batteries. However, large-scale application of NFS is highly impeded by its low electrical conductivity, which leads to poor cyclability and rate capability. To address these issues, we introduce rice husk-derived carbon with engineered porosity and structure as carrier to load active material NFS. The resultant hybrid material delivers extremely high specific charge capacity of 113.4 mAh g−1 at 0.1 C (1 C = 120 mA g−1), and a large reversible capacity of 81.2 mAh g−1 is retained after 100 cycles with a high retention rate of about 83.9%. The capacity of the composite can reach 60 mAh g−1 even at the current density 5 C. These excellent electrochemical performances are attributed to a favorable combination of the interpenetrating conductive carbon framework and ordered mesoporous structure that maintain well-balanced ionic and electronic conductivities throughout the electrode.

A first-principles investigation of the influence of polyanionic boron doping on the stability and electrochemical behavior of Na3V2(PO4)3.

Na3V2(PO4)3 (NVP) is one of the most promising candidates for use as cathodes in room-temperature sodium ion batteries owing to its high structural stability and rapid Na+ transportation kinetics. The cationic doping of foreign ions at Na or V sites in the NVP lattice has proven to be an effective approach for enhancing the electrochemical performance of NVP. In this work, we present a first-principles density functional theory investigation of the impact of polyanionic boron doping at P sites on the structural and electrochemical behavior of NVP. Our simulation results suggest that B doping considerably increases the structural stability of NVP while shrinking its lattice size to some extent. Since B donates far fewer electrons to connected O atoms, the surrounding V atoms become more positive, causing the operating voltage to increase with B content. However, the reduction in lattice size is not beneficial for the Na+ transportation kinetics. As demonstrated by a search for the transition state, a concerted ion-exchange mechanism is preferred for Na+ transportation, and increased B doping leads to a higher Na+ diffusion barrier. Improvements in electrochemical performance due to B doping see (Hu et al. Adv Sci 3(12):1600112, 2016) appear to originate mainly from the resulting increased electrical conductivity.

Barium Titanate-Based Porous Ceramic Flexible Membrane as a Separator for Room-Temperature Sodium-Ion Battery.

Sodium-ion batteries (NIBs) are an alternative low-cost battery technology for large-scale energy storage application, and the development of high-performance polymer-based electrolytes is crucial for further advancement of low-cost NIBs. Though electrode materials provide significant contribution to the energy density of the battery, the separator plays a vital role in deciding the safety, duration, and performance of batteries. The glass fiber membrane is considered as the most compatible separator for NIBs because of its high ionic conductivity and reasonable performance. However, the leakage and flammability of the liquid electrolytes while using the glass fiber separator can lead to safety issues. Therefore, herein, we present an alternative approach for the first time to replace the glass fiber separator in NIBs using the porous ceramic membrane (PCM). The polymer blend-based PCM is prepared by a simple solution-casting technique and used as the separator in NIBs. The good thermal stability of the PCM up to 400 °C, high ionic conductivity of about 10-3 S cm-1, high electrolyte uptake, and porous nature make it a better choice over the glass fiber membrane. To demonstrate the applicability of PCM in NIBs, the sodium-ion storage property of hard carbon is evaluated using the PCM as the separator at room temperature. The specific capacity of hard carbon using the PCM-based separator is about 270 mA h g-1 at a current density of 30 mA g-1 which is ∼23% higher than the glass fiber separator (208 mA h g-1) at the same current density. The enhancement in specific capacity is due to the compatibility of the PCM with sodium electrodes, low interfacial resistance, high sodium-ion transference number (0.8), and good electrochemical stability (4.9 V) than the glass fiber separator. This study demonstrates a promising alternative separator to the glass fiber membrane, which can lead to the development of a practical and safe NIB.

Electrochemical Properties and Challenges of Type II Silicon Clathrate Anode in Sodium Ion Batteries

The development of advanced anodes for low-cost room temperature sodium-ion batteries (SIBs) with high cycling stability is of great significance. Silicon clathrates are promising intercalation anodes due to their cage-like frameworks. It is predicted that the open cages can easily accommodate alkali ions with negligible volume changes. However, the complicated surface structure and chemical reactions make it challenging to understand the electrochemical performance of clathrate anodes in SIBs. In this paper, we evaluated the performance of type II clathrate anodes in SIBs. A slightly elevated testing temperature (45°C) is shown to improve the cell capacity and rate performance due to the improved ionic conductivity. However, side reactions on the solid electrolyte interface (SEI) and loss of active material during the first sodiation process contribute to the low Coulombic efficiency during the first cycle. Analysis is supported by electrode morphology, elemental mapping, and X-ray photoelectron spectroscopy (XPS) on the clathrate electrodes at different electrochemical states. Na+ ion transport behavior between clathrate cages and surface in terms of migration barriers was also computed to explain the positive effect of higher cell testing temperature, and the low Coulombic efficiency of the first cycle.

High-Performance P2-Na0.70Mn0.80Co0.15Zr0.05O2 Cathode for Sodium-Ion Batteries.

Room-temperature sodium-ion batteries (NIBs) using a manganese-based layered cathode have been considered promising candidates for grid-scale energy storage applications. However, manganese-based materials suffer from serious Jahn-Teller distortion, phase transition, and unstable interface, resulting in severe structure degradation, sluggish sodium diffusion kinetics, and poor cycle, respectively. Herein, we demonstrate a Zr-doped Na0.70Mn0.80Co0.15Zr0.05O2 material with much improved specific capacity and rate capability compared with Zr-free Na0.70Mn0.85Co0.15O2 when used as cathode materials for NIBs. The material delivers a reversible capacity of 173 mA h g-1 at 0.1 C rate, corresponding to approximately 72% of the theoretical capacity (239 mA h g-1) based on a single-electron redox process, and a capacity retention of 88% after 50 cycles was obtained. Additionally, a homogenous solid-state interphase (SEI) film was revealed directly by high-resolution transmission electron microscopy in Zr-doped material after battery cycling. Electrochemical impedance spectroscopy proves that the formation of SEI films provides the Zr-doped material with special chemical/electrochemical stability. These results here give clear evidence of the utility of Zr-doping to improve the surface and environmental stability, sodium diffusion kinetics, and electrochemical performance of P2-type layered structure, promising advanced sodium-ion batteries with higher energy density, higher surface stability, and longer cycle life compared with the commonly used magnesiumdoping method in electrode materials.

Ultrahigh rate sodium-ion storage of SnS/SnS2 heterostructures anchored on S-doped reduced graphene oxide by ion-assisted growth

Developing high-performance anode materials is very crucial for room-temperature sodium-ion batteries (SIBs). Sn-based compounds are promising SIB anode materials for their high theoretical capacities and low costs. However, the intrinsic low conductivity, poor infiltration and irreversible reactions of Sn-based compounds lead to poor rate and cycling performance. In order to address above issues, SnS/SnS2 heterostructures on sulfur-doped reduced graphene oxide (SG) are assembled via a facile alkali ion-assisted growth. As-synthesized SnS/SnS2 heterostructures on SG with assistance of K+, denoted as SnS/SnS2@SG-K, exhibits typical layer-stacked structure and high reversible capacities over 800 mAh g−1 at 50 mA g−1 and 241 mAh g−1 even at a record high current density of 48 A g−1, which are superior to most of the Sn-based SIB anode materials. The excellent rate and cycling performance of SnS/SnS2@SG-K could be ascribed to the layer-stacked structures of SG and heterojunctions between SnS and SnS2 which can accelerate semi-infinite diffusions of Na+ ions and electrons, alleviate polysulfide shuttling problems and reduce volume fluctuation effect. Meanwhile, the pseudocapacitance of oxygen and sulfur-containing groups in SG also contribute to the unprecedented sodium storage performance of as-synthesized SnS/SnS2@SG-K.

Development of Nitrate Combustion Synthesized NVP-Type Cathode and Glucose-Derived Hard Carbon Anode for Sodium-Ion Battery Single Cells

The synthesis and characterization of a Na3V2(PO4)3 cathode material for room-temperature sodium-ion battery is reported. The NVP material was prepared by a two-step process via sol-gel nitrate combustion method for precursor preparation and subsequent pyrolysis under Argon. Sodium-ion batteries have emerged as a promising candidate for large-scale energy storage due to sodium’s abundance and low cost of raw materials. However, in order to justify lower energy densities compared to Li-ion systems, Co-containing cathodes have to be avoided.[1,2] The materials have been investigated using SEM, EDX, XRD and TOF-SIMS methods. Electrochemical characterization has been carried out using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge/discharge method (GCD). The electrode slurry was prepared by mixing the active material, conductive additive (Super P) and polyvinylidene difluoride (PVdF) binder in a 75:15:10 mass ratio. The mixed slurry was cast onto aluminium foil using doctor-blade technique. The cast electrodes were dried under vacuum for 24h. The half-cells (EL-Cell GmbH) were assembled and electrolyte mixtures prepared in an Argon-filled glovebox (O2 < 0.1 ppm, H2O < 0.1 ppm). Sodium metal was used as counter and reference electrode and 1M NaClO4 in propylene carbonate (PC) as the electrolyte in half-cell measurements. SEM image of the NVP cathode surface in Fig. 1a shows homogeneous distribution of NVP particles and Super P carbon. The NVP particles are of 300 – 500 nm in diameter. The rate-performance of the NVP electrode (Fig. 1b) can be improved by creating a carbon shell around the particles. The results of single cell measurements for optimized NVP cathode and Glucose-derived Hard Carbon [3–5] anode will be discussed. Acknowledgements The present study was supported by European Regional Development Fund (Centres of Excellence TK141 (2014-2020.4.01.15-0011) and TK117 (3.2.0101–0030), TeRa project SLOKT12026T, Higher education specialization stipends in smart specialization growth areas 2014-2020.4.02.16-0026), “Institutional development programme for research and development and higher education institutions” (ASTRA) (Graduate School of Functional Materials and Technologies, Materials Technology Projects SLOKT12180T and SLOKT12181T, Energy Technology Project SLOKT10209T), Estonian Research Council (Institutional Research Grant IUT20–13, Personal Research Grant PUT1033 and by NAMUR project 3.2.0304.12-0397. Mr. Väli thanks Estonian Students Fund in USA for financial support. References British Geological Survey - Risk List 2015, British Geological Survey, (2015) http://nora.nerc.ac.uk/513472/1/Risk_List_2015_FINAL.pdf.Y.-K. Sun, D.-J. Lee, Y. J. Lee, Z. Chen, and S.-T. Myung, ACS Appl. Mater. Interfaces, 5, 11434 (2013).R. Väli, A. Jänes, T. Thomberg, and E. Lust, J. Electrochem. Soc., 163, A1619 (2016).R. Väli, A. Jänes, and E. Lust, J. Electrochem. Soc., 164, E3429 (2017).R. Väli, A. Jänes, T. Thomberg, and E. Lust, Electrochimica Acta, 253, 536 (2017). Figure 1

Self-doping of Ti3+into Na2Ti3O7 increases both ion and electron conductivity as a high-performance anode material for sodium-ion batteries

As a safe, low-voltage anode material, in recent years, Na2Ti3O7 has become regarded as a highly alternative negative material for high energy room-temperature sodium ion batteries. However, its poor ion and electron conductivity produces very poor electrochemical performance of Na2Ti3O7, therefore greatly limiting its practical application in future scalable utilization. We report here a self-doping of Ti3+ into the Na2Ti3O7 electrode material, through a very simple post heat-treatment process, that is, annealing the Na2Ti3O7 precursor at an argon atmosphere containing 5% H2. By XPS characterization, it is confirmed that Ti3+ is successfully doped into Na2Ti3O7. Benefiting from this self-doped Ti3+ with larger ionic radius and better electronic conductivity, the obtained Na2Ti3O7 demonstrates improved electron conductivity and ion diffusion properties. Combined with a carbon coating, this self-doped Na2Ti3O7 electrode material exhibits superior electrochemical performance to that of non-doped electrode, e.g., this Na2Ti3O7 sample could delivers a specific capacity of 187.8 and 51.9 mAh g−1 from 0.1C to 10C at various rate of discharge, respectively. When recycled back to 0.1C, it can still reach 153 mAh g−1. Compared with numerous reported nanoscale means, we believe this approach is practical and productive, and may extend to other ti-based electrode materials.