Solid-state Sodium-ion Batteries Research Articles

Ionic Conductivity Analysis of NASICON Solid Electrolyte Coated with Polyvinyl-Based Polymers

The global environmental crisis necessitates reliable, sustainable, and safe energy storage solutions. The current systems are nearing their capacity limits due to the reliance on conventional liquid electrolytes, which are fraught with stability and safety concerns, prompting the exploration of solid-state electrolytes, which enable the integration of metal electrodes. Solid-state sodium-ion batteries emerge as an appealing option by leveraging the abundance, low cost, and sustainability of sodium. However, low ionic conductivity and high interfacial resistance currently prevent their widespread adoption. This study explores polyvinyl-based polymers as wetting agents for the NASICON-type NZSP (Na3Zr2Si2PO12) solid electrolyte, resulting in a combined system with enhanced ionic conductivity suitable for Na-ion solid-state full cells. Electrochemical impedance spectroscopy (EIS) performed on symmetric cells employing NZSP paired with different wetting agent compositions demonstrates a significant reduction in interfacial resistance with the use of poly(vinyl acetate)—(PVAc-) based polymers, achieving an impressive ionic conductivity of 1.31 mS cm−1 at room temperature, 63.8% higher than the pristine material, notably reaching 7.36 mS cm−1 at 90 °C. These results offer valuable insights into the potential of PVAc-based polymers for advancing high-performance solid-state sodium-ion batteries by reducing their total internal resistance.

Research Progress on the Solid Electrolyte of Solid-State Sodium-Ion Batteries

Research Progress on the Solid Electrolyte of Solid-State Sodium-Ion Batteries

The Crystallization Behavior of a Na2O-GeO2-P2O5 Glass System: A (Micro)Structural, Electrical, and Dielectric Study.

Sodium-phosphate-based glass-ceramics (GCs) are promising materials for a wide range of applications, including solid-state sodium-ion batteries, microelectronic packaging substrates, and humidity sensors. This study investigated the impact of 24 h heat-treatments (HT) at varying temperatures on Na-Ge-P glass, with a focus on (micro)structural, electrical, and dielectric properties of prepared GCs. Various techniques such as powder X-ray diffraction (PXRD), infrared spectroscopy-attenuated total reflection (IR-ATR), and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) were employed. With the elevation of HT temperature, crystallinity progressively rose; at 450 °C, the microstructure retained amorphous traits featuring nanometric grains, whereas at 550 °C, HT resulted in fully crystallized structures characterized by square-shaped micron-scale grains of NaPO3. The insight into the evaluation of electrical and dielectric properties was provided by Solid-State Impedance Spectroscopy (SS-IS), revealing a strong correlation with the conditions of controlled crystallization and observed (micro)structure. Compared to the initial glass, which showed DC conductivity (σDC) on the order of magnitude 10-7 Ω-1 cm-1 at 393 K, the obtained GCs exhibited a lower σDC ranging from 10-8 to 10-10 Ω-1 cm-1. With the rise in HT temperature, σDC further decreased due to the crystallization of the NaPO3 phase, depleting the glass matrix of mobile Na+ ions. The prepared GCs showed improved dielectric parameters in comparison to the initial glass, with a noticeable increase in dielectric constant values (~20) followed by a decline in dielectric loss (~10-3) values as the HT temperatures rise. Particularly, the GC obtained at @450 stood out as the optimal sample, showcasing an elevated dielectric constant and low dielectric loss value, along with moderate ionic conductivity. This research uncovers the intricate relationship between heat-treatment conditions and material properties, emphasizing that controlled crystallization allows for precise modifications to microstructure and phase composition within the remaining glassy phase, ultimately facilitating the fine-tuning of material properties.

Probing the Dynamic Na Metal/Nasicon Interface in Sodium-Ion Batteries

Interest in solid-state sodium-ion batteries (SSIBs) have resurged remarkably as a means of diversification in energy storage devices to address climate issues and further propelled by the movement of ‘Beyond-Li’. State of the art SSIBs not only offer energy security and sustainability but also comparable power and energy densities to their counter-parts. Yet to fully capitalise on the technology, the fundamental processes taking place between the anode and interface or ‘point of contact’ needs to be understood. Previous iterations of SSIBs have employed various solid-electrolyte candidates – most notable being beta-alumina – however with the recent advancements in synthesis and dopants more prominent solid-electrolytes have become interesting, one in particular being NaSICON (Sodium Super Ionic Conductor). NaSICON has several advantages, one of which is the reduction in operating temperatures of SSIBs due to its inherent fast sodium-ion transport1. This would broaden the potential applications of SSIBs, making the technology more accessible to a wider range of markets.Current perspectives on NaSICON solid-electrolytes have focused on optimising conductivity through means of additive dopants2 and synthesis procedures3. Yet at present, the understanding of the fundamentals of interfacial inhomogeneities that affect the performance of these materials in SSIBs is limited. With consideration of the direct implications on performance that surface chemistry has, understanding of this is paramount.Evaluation of the chemical evolution of the Na metal/NaSICON interface has been achieved through assessing the changes of the chemical landscape that take place at the surface and near-surface, through surface characterisation techniques that probe the area of interest at varying depths – X-Ray Photoelectron Spectroscopy (XPS) and Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS). This has been conducted on samples that have been electrochemically cycled and comparison made to samples in pristine condition. The compositions used to conduct this investigation are Na3Zr2Si2PO12 and Na3.4Zr2Si2.4P0.6O12 – the latter of which has been shown to have one of the highest room temperature sodium-ion conductivity4. Through this, the electronic structure, and hence chemical state, can be deduced alongside a 3D chemical map that will correlate surface chemical changes with electrochemical performance. Thus, a preliminary means of understanding the fundamentals of chemical evolution can be established. References Lu, G. Xia, J. P. Lemmon, Z. Yang, ‘Advanced materials for sodium-beta alumina batteries: Status, challenges and perspectives’, Journal of Power Sources, Vol. 195, p. 2431-2442, 2010. Samiee, B. Radhakrishnan, Z. Rice, Z. Deng, Y. Meng, S. Ong, J. Luo, ‘Divalent-doped Na3Zr2Si2PO12 natrium superionic conductor: Improving the ionic conductivity via simultaneously optimizing the phase and chemistry of the primary and secondary phases’, Journal of Power Sources, Vol. 347, p. 229-237, 2017. Jalalian-Khakshour, C. Phillips, L. Jackson, T. Dunlop, S. Margadonna, D. Deganello, ‘Solid-state synthesis of NASICON (Na3Zr2Si2PO12) using nanoparticle precursors for optimisation of ionic conductivity’, Journal of Materials Science, Vol. 55, 2020. Ma, C-L. Tsai, X-K. Wei, M. Heggen, F. Tietz, J. T. S. Irvine, ‘Room temperature demonstration of a sodium superionic conductor with grain conductivity in excess of 0.01 S cm−1 and its primary applications in symmetric battery cells’ J. Mater. Chem. A, Vol. 7, p. 7766-7776, 2019.

Investigation of Aliovalent Substitution in the Solid Sodium Ion Electrolyte Na2ZrCl6

The research community is working hard on the development of solid-state batteries (SSB) as an alternative to commercialized lithium-ion batteries, due to their higher energy density and enhanced safety. One of the core research areas of SSBs is the solid-state electrolyte (SE), which should fit the demand for high ionic conductivity and electrochemical stability at the same time. Recently, halide SEs have emerged because they are mechanochemical processable, similar to sulfidic SEs, but halide SEs exhibit excellent electrochemical oxidation stability compared to sulfidic SEs [1,2].However, the relatively low ionic conductivity at room temperature still hinders the application of halide SE in SSBs. Aliovalent substitution is a very widely used method to improve the ionic conductivity of SEs [3,4]. We are also motivated by the application of earth-abundance elements to reduce raw material costs.Recently, significant focus has been gained by Zr-based compounds such as Na2ZrCl6. We investigate here such compounds, focusing on elemental substitutions to gain increased ionic conductivity and on gaining insight into the influence of synthesis on SE crystal structure and electrochemical properties.In our work, different amounts of elemental substitutions are investigated, and the related materials are synthesized at different temperatures. In particular, the influence of a series of subsequent heating temperatures on the structure of the binary system is studied through XRD diffraction analysis and further refinement. The Ionic diffusion paths are also estimated through the band valence sum approach, in order to validate the electrochemical impedance spectroscopy (EIS) results.In summary, we report our early results on the development of novel solid electrolytes for Na-based solid-state batteries.REFERENCES[1] Kwak, H.; Lyoo, J.; Park, J.; Han, Y.; Asakura, R.; Remhof, A.; Battaglia, C.; Kim, H.; Hong, S.-T.; Jung, Y. S. Na2ZrCl6 enabling highly stable 3 V all-solid-state Na-ion batteries. Energy Storage Mater. 2021, 37, 47−54.[2] Tong Zhao, Alexander N. Sobolev, Roman Schlem, Bianca Helm, Marvin A. Kraft and Wolfgang G. Zeier. Synthesis-Controlled Cation Solubility in Solid Sodium Ion Conductors Na2+xZr1 - xInxCl6. ACS Appl. Energy Mater. 2023, XXXX, XXX, XXX-XXX.[3] Schlem, R.; Banik, A.; Eckardt, M.; Zobel, M.; Zeier, W. G. Na3-xEr1-xZrxCl6-A Halide-Based Fast Sodium-Ion Conductor with Vacancy-Driven Ionic Transport. ACS Appl. Energy Mater. 2020, 3, 10164−10173.[4] Wu, E. A.; Banerjee, S.; Tang, H.; Richardson, P. M.; Doux, J.M.; Qi, J.; Zhu, Z.; Grenier, A.;Li, Y.; Zhao, E.; Deysher, G.; Sebti, E.;Nguyen, H.; Stephens, R.; Verbist, G.; Chapman, K. W.; Clement, R.J.; Banerjee, A.; Meng, Y. S.; Ong, S. P. A stable cathode-solid electrolyte composite for high-voltage, long-cycle-life solid-state sodium-ion batteries. Nat. Commun. 2021, 12, 1256.

Computational Investigation of Halide Solid Electrolytes for Na-Based Batteries

Significant scientific and economic challenges are presented by developing battery systems with increased energy storage capacity. Geopolitical issues might pose supply chain risks for lithium (Li)-ion batteries, which are frequently used in portable electronics. As an alternative, sodium-ion batteries (NIBs), have drawn attention from researchers all over the world due to the perspective of being lower cost systems[1]. In comparison to lithium-ion batteries, solid-state sodium-ion batteries (SSSBs) promise as a safe, scalable, and environmentally friendly alternative. For the production of robust and adaptable SSSBs, the development of highly conductive, electrochemically stable, and chemically stable solid electrolytes (SEs) is essential [2]. With greater durability, adaptability, and safety, solid-state batteries with inorganic solid electrolytes are being heavily investigated as safer and perhaps more energy-dense alternatives to liquid electrolyte cells.Sulfides solid electrolytes have been extensively investigated due to their mechanical softness and high ionic conductivity. However, the electrochemical oxidation stability of those materials are as low as 2 V (vs. Na+/Na)[3]. Alternatively, the excellent ion conductivities and stability at high potentials have made halide compounds, intriguing candidates for solid electrolytes in batteries. These compounds offer fast ion transport, good stability at highly oxidative potentials, and are easily processed. A wide range of chemistries, such as A3MX6 (A = Li, Na; M = Sc, In, Y, Yb, Er, Hf, Ho, Dy, Al, Zr; X = F, Cl, Br, I), have been synthesized with tunable properties and the characterizations of those materials shows relevant electrochemical proprieties [2].In our work, we investigate different Na-based chloride compounds by Density Functional Theory (DFT). We expand beyond the reported compositions to consider possible cation-substituted compounds. Here, we report on the structures, ionic conduction pathways and ionic conductivity (computed by molecular dynamics methods) expected for such compounds. In the next months, we will also evaluate the compounds´ chemical and electrochemical stability. Our work moves us one step closer towards the development of stable and highly conductive solid electrolytes for Na-based solid-state batteries.References :[1] J. Mater. Chem. A, 2021,9, 281-292[2]J. Mater. Chem. A, 2022,10, 21565-21578[3] ACS Energy Lett. 2022, 7, 10, 3293–3301

Halide Heterogeneous Structure Boosting Ionic Diffusion and High-Voltage Stability of Sodium Superionic Conductors.

The development of solid-state sodium-ion batteries (SSSBs) heavily hinges on the development of an superionic Na+ conductor (SSC) that features high conductivity, (electro)chemical stability, and deformability. The construction of heterogeneous structures offers a promising approach to comprehensively enhancing these properties in a way that differs from traditional structural optimization. Here, this work exploits the structural variance between high- and low-coordination halide frameworks to develop a new class of halide heterogeneous structure electrolytes (HSEs). The halide HSEs incorporating a UCl3 -type high-coordination framework and amorphous low-coordination phase achieves the highest Na+ conductivity (2.7 mS cm-1 at room temperature, RT) among halide SSCs so far. By discerning the individual contribution of the crystalline bulk, amorphous region, and interface, this work unravels the synergistic ion conduction within halide HSEs and provides a comprehensive explanation of the amorphization effect. More importantly, the excellent deformability, high-voltage stability, and expandability of HSEs enable effective SSSB integration. Using a cold-pressed cathode electrode composite of uncoated Na0.85 Mn0.5 Ni0.4 Fe0.1 O2 and HSEs, the SSSBs present stable cycle performance with a capacity retention of 91.0% after 100 cycles at 0.2 C.

A flexible and free-standing composite solid electrolyte with a pomegranate-like structure for solid-state sodium-ion batteries

Solid sodium-ion batteries have the advantages of high energy density and good safety and are considered promising candidates for the next generation of energy storage systems. However, the sizeable interfacial resistance and dendrite growth between sodium and solid electrolytes, especially at high current densities, severely limit their development. Polymer-ceramic composite electrolytes are considered one of the potential candidates for solid electrolytes with high ionic conductivity and soft interface contact. In this study, a flexible self-supporting composite solid electrolyte with a pomegranate structure was prepared by a simple solution casting method. The addition of Na3Zr2Si2PO12 filler significantly improved the mechanical strength and electrochemical stability of the composite polymer electrolyte (CPE). The electrochemical stability window increases to 4.8 V relative to Na/Na+, and the conductivity reaches 1.069 × 10−4 S cm−1 at room temperature. Solid-state Na3V2(PO4)3/Na batteries using this CPE exhibit high cycle stability, with a high capacity retention rate at 1C (95.13%, coulomb efficiency of >98% after 290 cycles). These results indicate that PVDF-based CPE doped with inorganic Na3Zr2Si2PO12 packing is a promising composite electrolyte for solid sodium-ion batteries.

High-Entropy Layered Oxide Cathode Enabling High-Rate for Solid-State Sodium-Ion Batteries

HighlightsHigh-entropy oxides O3-Na0.95Li0.06Ni0.25Cu0.05Fe0.15Mn0.49O2 cathode constructed by compatible radius and different Fermi level ions was designed for solid-state Na-ion batteries.Na0.95Li0.06Ni0.25Cu0.05Fe0.15Mn0.49O2 cathode exhibits high-rate performance, air stability and electrochemically thermal stability.A series of characterizations were performed to explore energy storage mechanism of Na0.95Li0.06Ni0.25Cu0.05Fe0.15Mn0.49O2.

Scalable Synthesis of Selenide Solid-State Electrolytes for Sodium-Ion Batteries.

Solid-state sodium-ion batteries employing superionic solid-state electrolytes (SSEs) offer low manufacturing costs and improved safety and are considered to be a promising alternative to current Li-ion batteries. Solid-state electrolytes must have high chemical/electrochemical stability and superior ionic conductivity. In this work, we employed precursor and solvent engineering to design scalable and cost-efficient solution routes to produce air-stable sodium selenoantimonate (Na3SbSe4). First, a simple metathesis route is demonstrated for the production of the Sb2Se3 precursor that is subsequently used to form ternary Na3SbSe4 through two different routes: alcohol-mediated redox and alkahest amine-thiol approaches. In the former, the electrolyte was successfully synthesized in EtOH by using a similar redox solution coupled with Sb2Se3, Se, and NaOH as a basic reagent. In the alkahest approach, an amine-thiol solvent mixture is utilized for the dissolution of elemental Se and Na and further reaction with the binary precursor to obtain Na3SbSe4. Both routes produced electrolytes with room temperature ionic conductivity (∼0.2 mS cm-1) on par with reported performance from other conventional thermo-mechanical routes. These novel solution-phase approaches showcase the diversity and application of wet chemistry in producing selenide-based electrolytes for all-solid-state sodium batteries.

Sandwiched composite electrolyte with excellent interfacial contact for high-performance solid-state sodium-ion batteries

Solid-state sodium-ion batteries have attracted significant attention due to their rich resources, high safety, and high energy density. However, the lower ionic conductivity and inferior interfacial contact between solid-state electrolytes (SSEs) and electrodes limit their practical applications. Herein, polyvinylideneuoride-co-hexauoropropylene (PVDF-HFP) membrane is selected and a novel sandwiched composite PVDF-HFP/Na2.5Zr1.95Ce0.05Si2.2P0.8O11.3F0.7/PVDF-HFP (G-NZC0.05SPF0.7-G) SSEs is well designed. The ionic conductivity of Na3Zr2Si2PO12 is enhanced by Ce4+/F− co-doping. The effects of Ce4+ and F− doping on the crystal structure, density, and ionic conductivity for Na3Zr2Si2PO12 are well investigated. The optimal NZC0.05SPF0.7 delivers a high ionic conductivity of 1.39 × 10−3 S cm−1 at 25 ℃. Moreover, the PVDF-HFP membrane can significantly enhance the interface compatibility between NZC0.05SPF0.7 and electrodes. The as-prepared G-NZC0.05SPF0.7-G exhibits a large ionic conductivity of 1.07 × 10−3 S cm−1 at 25 ℃, wide electrochemical stability window up to 4.5 V, high critical current density of 1.2 A cm−2, and stable Na plating/stripping over 600 h at 0.3 A cm−2. The solid-state Na0.67Mn0.47Ni0.33Ti0.2O2/G-NZC0.05SPF0.7-G/Na battery delivers a remarkable cycling stability and rate capability at 25 ℃, indicating that the as-prepared G-NZC0.05SPF0.7-G has a promising application for solid-state SIBs. This study demonstrates an effective strategy to develop advanced solid-state electrolytes for solid-state SIBs.

Impedance analysis of PEG plasticized PEO-based composite polymer electrolytes for sodium-ion batteries

Solid-state sodium-ion batteries (SSIBs) will be the next generation batteries due to the high safety, low price, and availability of sodium resources. Composite polymer electrolytes (CPEs) are promising electrolytes because of easy fabrication, good stability, and high flexibility facilitating a good electrolyte–electrode interface, although their ionic conductivities are still unsatisfied. In this work, a CPE made of polyethylene oxide (PEO), Na3Zr2Si2PO[Formula: see text], and NaClO4 has been fabricated. To further enhance the ionic conductivity and a good electrolyte–electrode interface, polyethylene glycol (PEG) is added as a plasticizer. The electrochemical impedance spectroscopy (EIS) demonstrates effect on conductivity by introducing PEG.

Designing a Quasi-Liquid Alloy Interface for Solid Na-Ion Battery.

Solid-state sodium-ion batteries are attracting great attention due to their high energy density and high safety. However, the Na dendrite growth and poor wettability between sodium and electrolytes seriously limit its application. Herein, we designed a stable and dendrite-suppressed quasi-liquid alloy interface (C@Na-K) for solid sodium-ion batteries (SSIBs). The batteries exhibit excellent electrochemical performance thanks to better wettability and accelerated charge transfer and nucleation mode shifts. The thickness of the liquid phase alloy interface fluctuates along with the exotherm of the cell cycling process, which leads to better rate performance. The symmetrical cell can cycle steadily over 3500 h at 0.1 mA/cm2 at room temperature, and the critical current density can reach 2.6 mA/cm2 at 40 °C. The full cells with the quasi-liquid alloy interface also show outstanding performance; the capacity retention can reach 97.1%, and the average Coulombic efficiency can reach 99.6% of the battery at 0.5 C even after 300 cycles. These results proved the feasibility of using a liquid alloy interface of the anode for high-energy SSIBs, and this innovative approach to stabilizing the interface performance could serve as a basis for the development of next-generation high-energy SSIBs.

Mg-doped NASICON-type electrolyte for rechargeable solid-state sodium-ion batteries

Designing high sodium-ion conducting solid electrolytes is essential for realizing solid-state sodium-ion batteries. The present study investigates the earth-abundant divalent Mg2+ doping in the NASICON-type compound with a general compositional formula Na3.2+2xZr2-xMgxSi2.2P0·8O12 (x ranging from 0 to 0.228). Polycrystalline specimens are prepared via the conventional solid-state reaction method. A dominant monoclinic NASICON and the impurity m-ZrO2 exist in all the tested compositions. Na3PO4 and rhombohedral NASICON are also detected in compositions with high Mg2+ content. The conductivity significantly improves to 3.2 mS.cm−1 at 25 °C with maximum occurring at x = 0.128. The optimal microstructure, high excess Na content, expanded unit-cell volume, and conducting rhombohedral phase contribute to excellent conductivity in this composition. The electrochemical performance of various solid-state batteries with Na3·1V2P2·9Si0·1O12 electrode and optimized solid electrolyte is also evaluated. The symmetrical-cells having solid electrolyte/electrode interface modified by liquid electrolyte show a stable capacity of 70 mAh.g−1 after 70 cycles at C/10. Moreover, the solid-state half-cell in which a composite cathode is employed with no liquid electrolyte at the interface delivered a considerably high capacity of 92 mAh.g−1 at a C/5 rate. An outstanding energy density of ∼300 Wh.kg−1 at 25 °C demonstrates the exciting prospect of Na3·456Zr1·872Mg0·128Si2·2P0·8O12 electrolyte for rechargeable solid-state batteries.

Unveiling the role of multifunctional framework for high-energy P2-Na0.8Li0.12Ni0.22Mn0.66O2 cathode materials

Enhancing the interfacial stability between cathode active material and liquid/solid electrolyte is a vital step toward the development of high energy density sodium-ion batteries (SIBs). One of the challenges plaguing this field is an economical and feasible method to construct valid protective layers on cathode materials. Herein, an effective strategy based on synergetic effect of multifunctional framework by simultaneous surface NaTi2(PO4)3 (NTP) coating and bulk Ti4+ doping is designed to improve the performance of P2-Na0.8Li0.12Ni0.22Mn0.66O2 ([email protected]). The combined analysis of in-situ X-ray diffraction (in-situ XRD), scanning transmission electron microscopy (STEM) and density functional theory (DFT) calculations demonstrates that the multifunctional framework optimizes the lattice structure, improves the Ni oxidation states and enhances the stability of crystal and interfacial structure. [email protected] cathode displays high average discharge potential and fast diffusion of Na-ions and electrons. As a result, the [email protected] cathode reveals highly Na storage performance in both liquid-state and solid-state SIBs. The excellent capacity retentions after 500 cycles at 5 C in liquid-state batteries and after 100 cycles at 1 C in solid-state batteries are both close to 100%.

Recent advances in NASICON-type oxide electrolytes for solid-state sodium-ion rechargeable batteries

Recent advances in NASICON-type oxide electrolytes for solid-state sodium-ion rechargeable batteries

An asymmetric bilayer polymer-ceramic solid electrolyte for high-performance sodium metal batteries

Manufacturing an excellent solid electrolyte compatible with a high-voltage cathode is viewed as a critical tactic for improving the energy density of solid-state sodium-ion batteries (SSIBs). A novel asymmetric bilayer solid electrolyte of the PEO-SN-NaClO4|NZSP-NSO with an anti-reduction PEO-SN-NaClO4 layer close to the Na side is constructed by solution casting. The ionic conductivity is enhanced by using succinonitrile (SN) in polyethylene oxide (PEO) polymer electrolyte. The anti-oxidation layer of Na3Zr2Si2PO12 with Na2SiO3 (NZSP-NSO) is served as the support of the membrane on the cathode, which could improve the interface compatibility and electrochemical performance of SSIBs. The asymmetric bilayer solid electrolyte simultaneously features a wide electrochemical stability window (4.65 V vs. Na+/Na) and a high conductivity (2.68 × 10–4 S cm−1). Furthermore, the solid electrolyte demonstrates stable Na plating/stripping over 700 h and remarkably improves cycling stability in Na/Na3V2(PO4)3 batteries with an ultra-high capacity retention of 99.6% after 100 cycles at 50 °C and 0.5 C. This study provides an effective strategy for designing asymmetric high sodium ion conductivity solid-state electrolytes for high-performance SSIBs.

Na Plating and Stripping Using Highly Na-Ion Conductive Solid Polymer Electrolytes Based on Polyvinylidene Fluoride and Polyvinylpyrrolidone

Solid-state sodium-ion batteries (ss-SIBs) are a promising alternative to commercially available lithium-ion batteries (LIBs) for next-generation energy storage applications. They have lower production costs and are safer than LIBs. Moreover, sodium is more abundant than lithium. The incorporation of solid polymer electrolytes (SPEs) into SIBs has been attracting much more attention due to the easy processability, low costs, safe usability, modification scope, and abundance of polymers. However, SPEs for ss-SIBs with high ionic conductivity and low interfacial resistance between electrolytes and electrodes are lacking. In addition, SPEs face major challenges such as suitable manufacturing methods and the lack of knowledge about low-cost ss-SIBs assembly. Herein, using a facile solution casting process, we have successfully fabricated a high sodium-ion conductive composite SPE film based on polyvinylidene fluoride (PVDF) polymer, polyvinylpyrrolidone (PVP) binder, and NaPF6 salt. A comprehensive characterization has been conducted using X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Fourier Transform Infrared (FTIR), Thermogravimetric Analysis (TGA), Raman, and electrochemical impedance spectroscopy techniques to investigate the structural, thermal, and electrochemical performance of the as-prepared SPE films. High ionic conductivity (8.51 x 10-4 S cm-1 and 8.36 x 10-3 S cm-1 at 23°C and 78 °C, respectively) was observed from the SPE. A hybrid symmetric half-cell assembly (Na foil + 20 µL of 1 M NaClO4 in ethylene carbonate (EC) and propylene carbonate (PC) (EC: PC = 1:1) + Carbon-cloth |SPE| Carbon-cloth + 20 µL of 1 M NaClO4 in EC and PC (EC: PC = 1:1) | Na foil) showed excellent Na plating-stripping performance up to 8 mA cm-2 for 100 cycles. In addition, Na+ transfer mechanism in the composite electrolyte has been investigated using impedance and dielectric spectroscopy. The results indicate the promising applicability of SPEs in next-generation high-power rechargeable SIBs.

(Invited) Ion Conduction and Interface Stability of Sulfide Based Solid State Electrolytes – an Atomistic Perspective

All-solid-state batteries are promising in terms of safety as well as high energy density compared to the conventional organic liquid-based lithium batteries. However, the characteristic low ionic conductivity of solid-state electrolytes is a major challenge towards commercialization of solid-state sodium ion batteries. Sulfide-based electrolytes especially in amorphous form have been reported as promising solid electrolytes owing to their relatively high ionic conductivity at room temperature. However, a fundamental understanding of the local structure of these amorphous electrolytes and its subsequent impact on the ion transport could be instrumental in establishing guidelines for designing novel solid electrolytes. In the present work, we utilize first principles and classical atomistic simulations to characterize the local structure and investigate the ion transport in amorphous sulfide electrolytes. We selected sodium thiosilicate [xNa2S – (1-x) SiS2] and sodium thiophosphate [xNa2S – (1-x) P2S5] based electrolytes as a model system wherein we characterized the local structure, ion conduction mechanism and ultimately calculated the ionic conductivity of these electrolytes. We utilized experimental X-ray and neutron scattering data for model validation. Our theoretical calculations provide fundamental insights into ion conduction mechanisms as well as correlate ionic conductivity with electrolyte structure and composition.Along with ionic conductivity, interfacial stability is extremely important factor influencing the overall performance of solid-state batteries. Interfacial instability with sulfide electrolytes is detrimental to Li-ion transport, leading to poor cycling performance. Inherent thermodynamic instability of sulfide-based solid electrolytes drives the chemical reaction across the interface leading to formation of undesired secondary phases. The secondary phases are formed dynamically during the cycling and therefore a careful investigation into the dynamics at the electrolyte-cathode interfaces is crucial. To generate fundamental understanding of the interface stability, we utilized ab initio molecular dynamics (AIMD) simulations to carefully investigate the dynamics of secondary phase formation across the Li3PS4 | LiCoO2 interfaces. High-resolution microscopy and spectroscopy studies were used to complement the the first principles simulations methods and unravel the interphases formed under different cycling conditions. These calculations provide crucial insights into formation of secondary phases across the interface, which could be leveraged to evaluate possible avenues to inhibit formation of such undesirable secondary phases.

Ionic Conductivity, Na Plating–Stripping, and Battery Performance of Solid Polymer Na Ion Electrolyte Based on Poly(vinylidene fluoride) and Poly(vinyl pyrrolidone)

Solid-state sodium-ion batteries (ss-SIBs) are a promising alternative to commercially available lithium-ion batteries for next-generation energy storage applications due to the abundance and cost-effectiveness of sodium over lithium. Herein, using a facile solution casting process, a high sodium-ion conductive, filler-less composite solid polymer electrolyte (SPE) film based on poly(vinylidene fluoride) polymer, poly(vinyl pyrrolidone) (PVP) binder, and NaPF6 salt for ss-SIB has been successfully fabricated. Total conductivities of 8.51 × 10–4 and 8.36 × 10–3 S cm–1 at 23 and 83 °C, respectively, were observed from the SPE. A hybrid symmetric half-cell assembly using Na electrode and 1 M NaClO4 in ethylene carbonate (EC) and propylene carbonate (PC) (EC/PC = 1:1 wt %) electrolyte showed excellent Na plating–stripping performance at 10 mA cm–2 at 23 °C. The study showed that PVP binder played an important role in achieving good Na ion conductivity and excellent Na plating–stripping performance, highlighting the applicability of the as-prepared SPE in next-generation high-power rechargeable SIBs. A full cell with an SPE, a Na anode, and a Na3V2(PO4)3 cathode showed a discharge capacity of 93.2 mAh g–1 at 0.1 C with 86% capacity retention and 99.68% Coulombic efficiency for 100 cycles.