A niobium-substituted sodium superionic conductor with conductivity higher than 5.5 mS cm−1 prepared by solution-assisted solid-state reaction method

Metal-organic frameworks (MOFs), as a promising rechargeable electrochemical energy storage material have emerged in the field of solid-state lithium batteries. However, low ionic conductivity and high interfacial impedance still severely hamper the application of MOF-based solid-state electrolytes (SSE). In this work, a novel hierarchical porous H-ZIF-8 solid-state electrolyte (SSE) material is harvested through the in situ growth of zinc nitrate hydroxide nanosheets, expressing excellent ion conductivity of 1.04 × 10-3 Scm-1 and Li+ -transference number of 0.71. Moreover, the morphology and structure of H-ZIF-8 is further optimized to obtain a composite H-ZIF-8/HNT by decorating halloysite nanotubes (HNT). Notably, functionalized H-ZIF-8/HNT as an electrolyte presents obvious enhancement on electrochemical properties: higher ionic conductivity of 7.74 × 10-3 Scm-1 , better single-ion transmittability ( = 0.84), good interfacial compatibility as well as excellent rate performance. More importantly, the Li/LiFePO4 battery equipped with H-ZIF-8/HNT SSE has efficient lithium-dendrite suppression and up to 84% capacity retention (104.16mAhg-1 ) after 200 times galvanostatic charge/discharge cycles. This work enriches the solid-state lithium-ion composite electrolyte materials, opening an entirely new way for enhancing electrochemical performance.

Sodium is an earth abundant element, which makes sodium ion batteries a promising technology for grid-scale energy storage applications. Due to safety concerns with liquid electrolytes, extensive research has been carried out over the past decade to develop new solid-state electrolytes. However, developing solid-state electrolytes with relatively high ionic conductivity at room temperatures is a major challenge. Sulfide glasses have been reported to possess excellent ionic conductivity making them potential electrolytes for high performance sodium ion batteries. With an aim to develop novel electrolyte for high performance sodium ion batteries, our present work focuses on analyzing the local structure of sulfide glasses and its subsequent impact on transport properties through atomistic simulations, in conjunction with experimental characterization. As model systems, we studied x Na2S – (1-x) P2S5 glasses. The polarization and resonance effect of the P=S bonds in the glass complicates the parametrization of interatomic potentials necessary for classical MD simulations. Therefore, we employed ab initio MD simulations that perform quantum calculations on the fly while solving equations of motions at each MD step to accurately capture the complex chemistry. As model systems for our calculations, we considered a range of electrolytes with composition x Na2S – (1-x) P2S5 (x = 0, 0.33, 0.5, 0.6, 0.67, 0.75). The glasses were formed using melt-quench technique and the density of the glasses matched well (within 5%) with the experimentally measured value. We analyzed the local structure of these glasses by calculating the radial pair distribution functions (RDF’s) from ab initio MD and compared it to those obtained through X-ray scattering experiments to validate the model. The FTIR and NMR characterization of these glasses show presence of different structural units that effectively control the ionic conductivity of these glasses. We calculated the fractions of each of these functional units present in the glasses from ab initio MD. At 75% Na2S, all the sulfur present in the structure is non-bridging due to presence of purely [PS4]3- groups in the glass. At concentration lower than 75% Na2S, other structural units containing bridging sulfur such as [P2S7]4- dominate the local structure. On the other hand, at concentrations above 75% Na2S, additional structural units corresponding to [PS3]3- and polysulfides are observed along with [PS4]3- due to excess Na2S content. Increase in concentration of polysulfides leads to lower ionic conductivity. As a result, optimal ionic conductivity of these glasses is observed at 75 Na2S – 25 P2S5 composition. The calculated ionic conductivity of these glasses at room temperature was ~ 10-6 S/cm, which matches well in terms of order of magnitude with experimentally measured values. A relatively high ionic conductivity (~ 10-5 S/cm) can be achieved at slightly elevated temperatures of around 60 °C, making these sodium thiophosphate glasses promising electrolytes for solid-state sodium ion batteries.

A New Solid Li-ion Electrolyte from the Crystalline Lithium-Boron-Sulfur System

The last few decades have seen a drastic miniaturization of electronic devices following the famous Moore’s law predicted by Gordan Moore in 1971. These developments in the electronic industry have resulted in ultra-low-weight electronic devices such as palm-top computers, smart phones, tablet PCs etc. Batteries constitute one of the most important and essential components of these devices. At present, lithium ion batteries (LIBs) are considered the most suitable candidateforuseinportableelectronicdevices.However,thesebatteriesare available only in the bulk form and comprise a significant percentage of the overall weight of the device. As the miniaturization of electronic devices continues, we need more advanced batteries which are light weight, safe, and environment friendly. One possible solution is the development of thin film batteries (TFBs) which can be integrated onto the microprocessor chips themselves. For these applications, we would require solid-state (SS) electrolyte. Currently, a major obstacle in this field is the low ionic conductivity of SS electrolytes and high temperature needed to fabricate thin films of these materials. As far as the research in SS electrolyte materials is concerned, many different kinds of inorganic systems have been explored to date. These include Nasicon-type electrolytes, 1‐4 perovskite-type lithium lanthanum tantantes, 5,6 and garnet-type Li ion conductors. 7,8 Among all of them, garnet type Li7La3Zr2O12 (LLZO), synthesized lately by Weppner’s group 9 has been reported to possess very high ionic conductivity. What’s more, LLZO is electrochemically stable with a potential window wider than 0‐7 V, is environment friendly, and is relatively inexpensive. 9‐11 However, to our knowledge, LLZO has so far been synthesized in bulk form only; no work has been reported on the preparation of LLZO thin films. For realizing thin film batteries, it is essential to be able to grow thin films of solid electrolytes and preferably at low temperatures. In this paper, we are reporting the fabrication of LLZO thin films on SrTiO3 (100) and Sapphire (0001) substrates by pulsed laser deposition at room temperature. The effect of annealing was investigated by detailed characterization of thin film structures and properties. Studies were also performed to understand the influence of lithium loss during the deposition process.

All solid‐state sodium batteries (ASSBs) have attracted considerable attention due to their enhanced safety, long lifespan, and high energy density. However, several challenges have plagued the development of ASSBs, especially the relatively low ionic conductivity of solid‐state electrolytes (SSEs), large interfacial resistance, and low stability/compatibility between SSEs and electrodes. Here, a high‐performance all solid‐state sodium battery (NVP@C|PEGDMA‐NaFSI‐SPE|Na) is designed by employing carbon coated Na3V2(PO4)3 composite nanosheets (NVP@C) as the cathode, solvent‐free solid polymer electrolyte (PEGDMA‐NaFSI‐SPE) as the electrolyte and metallic sodium as the anode. The integrated electrolyte and cathode system prepared by the in situ polymerization process exhibits high ionic conductivity (≈10−4 S cm−1 at room temperature) and an outstanding electrolyte/electrode interface. Benefiting from these merits, the soft‐pack ASSB (NVP@C|PEGDMA‐NaFSI‐SPE|Na) delivers excellent cycling life over 740 cycles (capacity decay of only 0.007% per cycle) and maintains 95% of the initial reversible capacity with almost no self‐discharge even after resting for 3 months. Moreover, the bendable ASSB exhibits a high capacity of 106 mAh g−1 (corresponds to energy density of ≈355 Wh kg−1) at 0.5 C despite undergoing repeated bending for 535 cycles. This work offers a new strategy to fabricate high‐performance flexible ASSBs with a long lifespan and excellent flexibility.

Developing argyrodite-type, chlorine-rich, sodium-ion, solid-state electrolytes with high conductivity is a long-term challenge that is crucial for the advancement of all-solid-state batteries (ASSBs). In this study, chlorine-rich, argyrodite-type Na6-xPS5-xCl1+x solid solutions were successfully developed with a solid solution formation range of 0 ≤ x ≤ 0.5. Na5.5PS4.5Cl1.5 (x = 0.5), displaying a highest ionic conductivity of 1.2 × 10-3 S/cm at 25 °C, which is more than a hundred times higher than that of Na6PS5Cl. Cyclic voltammetry and electrochemical impedance spectroscopy results demonstrated that the rich chlorine significantly enhanced the ionic conductivity and electrochemical stability, in addition to causing a reduction in activation energy. The Na5.5PS4.5Cl1.5 composite also showed the characteristics of a pure ionic conductor without electronic conductivity. Finally, the viability of Na5.5PS4.5Cl1.5 as a sodium electrolyte for all-solid-state sodium batteries was checked in a lab-scale ASSB, showing stable battery performance. This study not only demonstrates new composites of sodium-ionic, solid-state electrolytes with relatively high conductivity but also provides an anion-modulation strategy to enhance the ionic conductivity of argyrodite-type sodium solid-state ionic conductors.

Fluoride ion conductors are developed for use as solid-state electrolytes in fluoride ion batteries which are one of promising candidates for next-generation storage batteries. Ba-doped LaF3 (La0.9Ba0.1F2.9: LBF) is mainly used as a solid-state electrolyte in fluoride ion batteries. However, room temperature conductivity of LBF is considerably low, on the order of 10−6 S cm−1 and it is still unclear the optimal elements to be doped to LaF3. In this study, we have explored La0.9Sr x Ba0.1−x F2.9 system (x = 0, 0.01, 0.025, 0.05, 0.1), in which Ba in LBF is substituted for Sr and investigated the composition dependence of ionic conductivity. We elucidate that the higher concentration of Sr without Ba can significantly improve the ionic conductivity, and the maximum ionic conductivity of La0.9Sr0.1F2.9 is 1.5 × 10−5 S cm−1 at room temperature, which is one order of magnitude larger than that of LBF. The higher ionic conductivity of LSF is due to the larger grain size and higher sintering density of LSF compared to LBF, which results in lower grain boundary resistance. The LSF total ionic conductivity of 10−4 S cm−1 can be achieved at 350 K, which significantly lowers operating temperature of fluoride ion batteries down to 350 K.

Thin-film solid oxide fuel cells are receiving increasing attention within the scientific community thanks to their high energy density and high efficiency in different temperature ranges. To be utilized as power supply systems for portable electronic devices, thin-film solid oxide fuel cells must demonstrate high power supply and low-temperature operation capabilities. Both capabilities are highly dependent on the function of the electrolyte layer, commonly comprised of ceramic mixed-ionic-electronic conductors [1]. The state-of-the-art thin-film solid oxide fuel cells utilize yttrium stabilized zirconia as an electrolyte material, despite its relatively low ionic conductivity within the typical working-temperature range of solid oxide fuel cells (up to 1000 °C). Moreover, the ionic conductivity of yttrium stabilized zirconia dramatically reduces with decreased temperature, limiting its performance as an electrolyte material for low-temperature (below 600 °C) solid oxide fuel cells [2].Gadolinia doped ceria is an alternative promising electrolyte material for low temperature solid oxide fuel cells. Its relatively high ionic conductivity below 600 °C makes it attractive as an electrolyte material although its partial electronic conductivity is a significant drawback [3]. This drawback is more pronounced in ultra-thin layers (sub-micron scale) solid oxide fuel cells devices. As a result, gadolinia doped ceria have been utilized only to a limited extent for thin-film solid oxide fuel cells.The issue of partial electronic conductivity might be resolved thanks to a non-conventional deposition technique of polycrystalline gadolinia doped ceria thin films. The proposed sputtering technique includes metallic alloy target and results in a granular morphology, as opposed to the columnar morphology obtained using the conventional sputtering method. As electrical conductivity of polycrystalline thin films is higher along the grain boundaries [4], gadolinia doped ceria layers with random crystallographic orientation are expected to be less electronically conductive. Here, we investigated the integration and the performance of granular gadolinia doped ceria as an electrolyte material for thin-film solid oxide fuel cells. The electronic-conduction properties along the grain boundaries of gadolinia doped ceria were studied, and a thin-film solid oxide fuel cell prototype was fabricated. Such devices with engineered grain boundaries hold the potential for low-temperature operation, high power output, and silicone-compatibility for novel integration opportunities and bulk-fabrication.

Computational prediction of fast ion conductor for all-solid-state lithium-ion batteries: A case study of Li3ZrI6

Poly(ionic liquid) iongel membranes for all solid-state rechargeable sodium battery

Solid‐state electrolytes (SSEs) are pivotal to advancing lithium metal batteries (LMBs). Electrochemically active LiCoO 2 (LCO) has high ionic conductivity (1.45 × 10 −3 S cm −1 at 35 °C), but its inherent electronic conductivity limits its application as an SSE. To address this limitation, a sandwich‐structured composite solid electrolyte (SSCSE) is presented by integrating an LCO layer between non‐electron‐conducting porous polypropylene (PP). This design decouples the electronic and ionic conductivities of LCO, enabling LCO to be an SSE for LMBs for the first time. Meanwhile, the intermediate fast‐ion conductor layer homogenizes Li⁺ flux and enhances mechanical strength, suppressing lithium dendrites growth and improving safety. Li||Li symmetric cell and Li||LFP full cell using LCO as the SSE achieve excellent performance (800 h at 0.5 mA cm −2 and 0.5 mAh cm −2 ; 93.6% capacity retention after 800 cycles with 99.8% coulombic efficiency). This breakthrough in utilizing LCO with high ionic conductivity as an SSE promotes the development of safer and higher energy‐density batteries.

All-solid-state sodium (Na) ion batteries (SiBs) are promising high-safety and low cost alternatives to current lithium (Li) ion batteries (LiBs), particularly suitable for the application to large-scale electrical energy storage systems. Development of inorganic solid Na-ion conducting materials used for solid electrolyte is most critical issue to realize all-solid-state SiBs. The solid electrolyte materials should have not only high Na-ion conductivity at room temperature but also chemical and electrochemical stabilities against both cathode and anode active materials. Oxide based solid electrolytes have lower conductivity and poorer deformability than sulfide based one, but they have other advantages such as their chemical stability in air and easiness for handling.Na2M2TeO6 (M = Zn, Mg, Ni, Co, etc.) with a P2-type honeycomb layered structure has been reported as a fast Na-ion conducting oxide [1]. Particularly, Na2Zn2TeO6 (NZTO) is an attractive candidate for a solid electrolyte material because of the high ionic conductivity well above 10-4 S cm-1 at room temperature, wide electrochemical potential window and lower densification temperature than other oxide-based Na-ion conductors such as NASICON and Na-β alumina [2–4]. On the other hand, Na2Ni2TeO6 (NNTO) has been investigated as a cathode active material for SiB operating at 3–4 V vs Na/Na+ [5,6]. Because of the similarity in their crystal structure and constituent elements, NNTO cathode and NZTO as solid electrolyte may be co-sintered without forming undesired secondary phases to fabricate all-solid-state SiBs.In this work, we investigated firstly the reactivity between NNTO and NZTO powders at annealing temperature between 500 ºC and 800 ºC in air. From XRD measurements, it was found that the reaction between NNTO and NZTO is negligible at annealing temperature below 700 ºC while when annealed at 800 ºC, they forms a solid-solution phase without forming any secondary phases. Based on this result, we fabricated NNTO-NZTO laminate via co-sintering NNTO and NZTO pellets at 700 ºC in air. Thicknesses of NNTO and NZTO layers in the laminate were set to 1 mm.From impedance measurements, apparent ionic conductivity of the NNTO-NZTO laminate was estimated to be approximately 0.1 mS cm-1 at 27 ºC, which is close to the prediction with taking into account only the conductivity of individually sintered NNTO (= 0.04 mS cm-1) and NZTO (= 0.36 mS cm-1) at 700 ºC. This indicates that the interfacial resistance between NNTO and NZTO layers is not so large. In addition, using the NNTO-NZTO laminate with NNTO layer thickness of 80 µm, electrochemical Na extraction reaction from NNTO layer through NZTO solid electrolyte was demonstrated via galvanostatic testing at room temperature. Obtained results are very fundamental but can be applied to fabricate all-solid-state SiBs with NNTO cathode and NZTO solid electrolyte via simple co-sintering process in future.

Three-dimensional (3D) battery architectures have been envisioned to enable high energy density electrodes without the associated power drop experienced by planar cells. However, the development of 3D cells is hampered by difficulties producing conformal solid-state electrolytes (SSE), solid polymer electrolytes (SPE) and gel polymer electrolytes (GPE) that are pinhole-free and have adequate ionic conductivities. Fortunately, electrolytes in 3D cells are often utilized at lower thickness, which may compensate the decreased ionic conductivity. Here, we comprehensively review potential 3D SSE, SPE and GPE electrolyte materials by compiling their thickness and room temperature ionic conductivity. We use area specific resistance (ASR) as a metric to compare 3D electrolytes with one another and conventional electrolytes. We find that certain process-material combinations, such as atomic layer deposition of SSEs, electrodeposition of SPEs and GPEs, and initiated chemical vapor deposition of SPEs demonstrate ASRs beneath the interfacial impedances of Li-based systems and approach state-of-the-art electrolytes. We also comment on additional factors, such as electrochemical stability, that should be evaluated when determining 3D electrolyte suitability. Future research should focus on adapting known materials chemistries for conformal deposition techniques to further improve the ionic conductivity, as these techniques are capable of producing the necessary thicknesses and conformality.

Solid-state sodium ion battery is a promising technology for energy storage in electrical grids. However, the characteristic low ionic conductivity of solid-state electrolytes is a major challenge towards commercialization of solid-state sodium ion batteries. Sulfide glasses have relatively high ionic conductivity at room temperature and are therefore considered promising as potential electrolytes. However, the energy barrier for ion hops in these electrolytes is highly sensitive to the chemical composition, which provides a tremendous opportunity to tailor the ionic conductivity. In-situ characterization of Na+ ion transport through experiments is extremely challenging. Atomistic simulations offer an economical route for determining the local structure of these glasses as well as Na+ ion transport mechanisms. Sodium sulfide – silicon sulfide [xNa2S – (1-x)SiS2] based electrolytes with varying compositions was chosen as a model system and atomistic simulations of various flavors were employed to determine ion conduction mechanism and evaluate ionic conductivity, each method having distinct advantages. Experimental X-ray scattering data was used for the purpose of model validation. Ab initio molecular dynamics (MD) simulations are able to accurately model the specific chemistry based on on-the-fly quantum mechanical calculations to determine interatomic interactions. Augmented with nudged elastic band analysis, these calculations can determine activation energies for ion hops. However, the maximum system size that can be realistically modeled using ab initio MD is limited to few hundred atoms and therefore cannot reliably calculate the bulk properties. On the other hand, classical MD simulations employ empirical forcefields to define pairwise interactions between constituent ions in these glasses. This method can simulate much larger systems comprising hundreds of thousands of atoms. However, the inability of these predefined forcefields to accurately capture the complex chemistry in sulfide glasses makes it extremely challenging to accurately model these glasses. Reactive force fields, such as ReaxFF, is based on a bond order potential in conjunction with charge equilibration that is based on extensive parameterization based on quantum mechanical calculations of structure and energies. ReaxFF forcefields are highly system specific. Classical MD simulations involving ReaxFF provide an effective route to accurately capture bond breakage and formation, while simulating considerably large systems (~ 100,000 atoms) and therefore accurately evaluates ionic conductivity. Based on simulation data from each of the above methods, their merits and demerits are discussed as pertains to the model system of sulfide glasses. We determined the ionic conductivities and activation energies for sodium ion hops and related them to the structural units and hop distances. Overall, these simulations provide fundamental insights into ion conduction mechanisms as well as correlate ionic conductivity with glass structure and composition. The combined approach demonstrates excellent promise in identifying optimal glassy electrolytes for sodium ion batteries.

For recent lithium-ion batteries (LIBs), there have been lots of researches about convert liquid-phase electrolyte to solid-state electrolyte (i. e. all-solid-state battery) to improve safety and stability. Solid-state electrolyte materials have to satisfy some criteria including high ionic conductivity at room-temperature, chemical stability against reducing environment, and mechanical strength. Many solid-materials for electrolyte have been researched, including perovskite, garnet, and sulfide-type of materials. Among them, garnet-type based lithium lanthanum zirconium oxide (LLZO, Li7La3Zr2O12) has been received attention due to its high ionic conductivity (~10-4 S/cm at room temperature) and wide electrochemical stability window (~6 V versus Li/Li+). The main issue of LLZO is the high interfacial resistance with anode and cathode materials such as Li metal and LiCoO2. Many researchers have tried to understand the cause of this interfacial resistance for LLZO. K. Park et al. researched about the cathode/electrolyte (LLZO) interface and revealed co-diffusion and second-phase formation of LLZO at high-temperature [1]. M. Zarabian et al. reported that spin-coated LLZO on the LiCoO2 pellet fabricated at low-temperature (~400oC) and co-diffusion of La and Co at the interface by using X-ray photoelectron spectroscopy (XPS) [2]. They commonly suggested that elevated temperature make chemical interaction and this make high interfacial resistance. In this study, we adopted novel sintering method, flash light annealing (FLA) process, to fabricate LLZO solid-electrolyte. This method is also called rapid, cool sintering because of its unique characteristics compared to conventional sintering methods [3]. FLA uses instantaneous high current to generate intensive pulsed light (IPL), and irradiate IPL toward the specimen to sinter the materials. Unlike the conventional sintering methods, this novel method has lots of advantages including availability of treatment at STP and fast sintering time (~ a few ms). Rapid sintering process gives no time for the diffusion at the interface, thus the interfacial resistance between cathode and LLZO solid-electrolyte must be reduced. We fabricated LLZO solid-electrolyte on the commercial LiCoO2 pellet by using solution-based spin-coating method and sintered the film by using FLA method. XPS and energy-dispersive X-ray spectroscopy (EDX) analysis were conducted to observe interface and diffusion of La and Co elements. Also, X-ray diffraction (XRD) method was used to investigate sintering ability of FLA through crystallinity development. The interfacial resistance between LiCoO2 and LLZO solid-electrolyte was analyzed by electrochemical impedance spectroscopy (EIS) through cross-plane set-up.