A new sintering mechanism, “silver-zipping”, for low-temperature sintering of oxide solid electrolytes

The sulfide-based all-solid-state batteries (ASSBs) has guaranteed having excellent safety by using non-combustible inorganic solid-electrolyte (SE). SE separator can transport Li ion selectively and there is no concentration gradient in theory, enabling fast charging. In addition, due to high ionic conductivity of sulfide-based SE comparable to liquid based electrolyte, high capacity and high energy density ASSBs of 5mAh cm-2 have been developed to a stage close to commercialization.So far, among the many issues of ASSBs, the performance improvement has been achieved by focusing on interfacial deterioration issues. However, recent several studies have analyzed and identified the cause of inhomogeneous reaction in composite cathode, which lead to capacity degradation quickly. It had been confirmed that the inhomogeneous reaction was caused by not only loosely contact and isolated active materials but also restriction Li conductivity in nano-crystal boundaries of active materials, resulting in localizing overcharge-discharge and decreasing in capacity and rate capability. As one of intrinsic properties of ASSBs, the solid-solid contact induce the limitation of lithium ion mobility and it also triggered insufficient electronic conduction pathway increasing charge transfer resistance.In order to develop high-energy density and high power ASSB, the ability of the conductivity for electron and ion must be balanced through the formation of a well-developed electronic percolating pathway. In this study, the inhomogeneous reactivity that can be maximized in thick electrodes is alleviated by improving the electron transfer path in the composite cathode. To uniformly transfer electrons in the composite cathode, we introduced argyrodite type SE coating with 2D conductive material under solvent environment. This approach is effective on forming a continuous electronic pathway for homogeneous reactivity as well as reduce SE oxidation by preventing direct contact between SE and cathode active material. As a result, we obtained a high initial capacity of 206 mAh g-1 using a single LiNi0.8Co0.1Mn0.1O2 cathode and SE coated with 2D conductive material, and confirmed that approximately 90% rapacity maintained after 200th cycle.

Recently, the use of liquid electrolytes in lithium batteries is prone to cause safety problems such as leakage and gas explosions. The PEO-based solid composite electrolytes (CE) for all-solid state batteries (ASSBs) have been studied for a possible replacement for liquid electrolytes. However, it results in degradation of mechanical properties and short circuit during cycling at the high temperature (60~80°C). Therefore, the thickness of electrolytes is required to be 150㎛ or more. However, to improve the energy density of all-solid state battery, it is required to reduce the thickness of the solid electrolyte layer to as low as 50㎛ and less. As a method for reducing the thickness, we suggested that the thin solid composite electrolyte film was composed of PEO/PVDF blending polymer as ionic conductor and binder including lithium salts and garnet LLZO powders. In addition, the composite cathode slurry was composed of NCM active material, Super P, Garnet-type LLZO powder and PEO/PVDF blending polymer. The electrochemical properties were measured by the AC impedance method, Linear Sweep Voltammetry, Symmetrical cell test and charge/discharge cell test. As a result, we will introduce the properties of CE with garnet LLZO powder, PEO and PVDF polymers in cathode and solid electrolyte layer. Finally, a pouch-type ASSBs having a bipolar structure in which energy density is improved by applying such a thin SE is described in more detail.

All-solid-state batteries (ASSBs) using inorganic solid electrolytes are expected to achieve high safety and high energy density as alternatives to conventional lithium-ion batteries using liquid electrolytes. However, in many cases, rate capability of ASSBs is poor compared with that of the conventional liquid system. This is because the contact interface between solid active materials and solid electrolyte is insufficient, resulting in high resistance for electrochemical properties. The solid electrode-electrolyte interface in ASSBs is related to the morphological structure such as porosity and mixed state. It has been confirmed that pressurization reduces the grain boundaries of solid electrolytes and improves conductivity1). From this improvement, it is generally known that applying high pressure when assembling ASSBs improves the contact area of the solid-solid interface, including electrode and electrolyte interface. However, the effect of pressure on particle-particle contact and battery performance is not understood enough. In this study, we investigated the effect of pressure-induced three-dimensional structure on the electrochemical properties of ASSBs by using X-ray computed tomography (CT). ASSBs were prepared at various stack pressures using a composite cathode consisting of oxide active materials LiNi1/3Co1/3Mn1/3O2 (NCM), sulfide solid electrolyte Li10GeP2S12 (LGPS), and acetylene black. Electrochemical properties were investigated in ASSBs of NCM composite cathode|LGPS solid-electrolyte|In-Li anode. The charge–discharge measurements were performed using various stack pressure, which indicates that the capacity increases as the stack pressure increases. To analyze the factors behind this result in terms of the internal structure of the ASSBs, we performed X-ray CT with synchrotron radiation at 20 keV using a homemade operando measurement cell that electrode diameter is 1 mm. This measurement system allows us to analyze the three-dimensional structure of composite cathode during monitoring applied pressure, electrochemical measurements, and X-ray CT measurements. From the X-ray CT data, we succeeded in quantifying the changes in the porosity of the composite cathode and the contact state between the active material and electrolytes by changing the pressure. Quantitative analysis revealed that the porosity and contact state correlate with the charge–discharge properties. Additionally, CT analysis revealed that the voids are preferentially presented near active materials and these voids spread the horizontal direction (not pressurization direction), resulting in different porosities of composite cathode and solid electrolyte layer. Since it was confirmed that voids remained in the vicinity of the active material even when the pressurization was continued, controlling these voids decreases the voids of the entire cathode layer. Pressure dependencies on AC impedance during X-ray CT measurements showed that the apparent conductivity of ASSBs increases linearly as the confinement stack pressure increases. This result is caused by suggesting that the decrease in porosity and tortuosity in cathode layer, which is detected by CT analysis. Additionally, date of tortuosity shows over-pressurization may bypass Lithium conduction path. The improved internal structure such as contact state due to pressurization enhances the apparent conductivity and charged-discharge characteristics of ASSBs. With the latest synchrotron radiation measurement technology and image processing technology, high-precision analysis has become possible.1) Jean-Marie Doux, Yangyuchen Yang, Darren H. S. Tan, Han Nguyen, Erik A. Wu, a Xuefeng Wang, Abhik Banerjeea and Ying Shirley Meng, J. Mater. Chem. A, 8, 5049, (2020).

Objective: Despite recent global efforts to establish all-solid-state batteries (ASSB) as potentially safe and stable high-energy and high-speed storage technology, long-term performance, specific power, and economic viability remain challenging. However, efficient and short ionic and electronic transport pathways and optimized interfacial contacts between the cell materials and compounds are essential. This poses a significant challenge for the microstructure of cathodes and a careful design and tailoring of anodes and separators in ASSB, which rely solely on solid-state contacts. Here, we present our recent work on ASSB with thiophosphate electrolytes conducted within the German Competence Cluster for Solid-State Batteries (FestBatt). Our work aims to investigate relevant parameters in different cell components on material, electrode, and cell level, such as the importance of particle size distributions, microstructures, and kinetic factors to optimize ASSB cathodes, separators, and anodes. Methodology: The work will be presented in four sections, which showcase key challenges as well as optimization strategies mainly focusing on cathode composites, but also discussing selected examples for separators and anodes in ASSB with thiophosphate electrolytes. Further, an outlook for relevant production steps of ASSB electrodes and cells will be given. For these studies, we mainly conducted focused ion beam scanning electron microscopy tomography, electrochemical impedance spectroscopy, cycling experiments on ASSB cells with thiophosphate solid electrolytes. Results: Fast conducting solid electrolytes are necessary to ensure sufficient transport in composite cathodes but does not represent the only key factor for high-quality cathode composites in ASSB. In our studies, we aimed to optimize the microstructure of composite cathodes consisting of intercalation-type active material and a thiophosphate-based solid electrolyte. We varied the particle size distribution of the solid electrolyte to create various cathode microstructures and assessed the effectiveness of electronic and ionic conduction pathways using partial conductivities. We used both electronically and ionically blocking electrodes for electrochemical impedance spectroscopy measurements to quantify the respective partial conductivities. Our analysis revealed that the particle size of the solid electrolyte significantly influences the charge transport and electrochemical performance of the cathodes. Additionally, using FIB-SEM tomography, we created detailed 3D reconstructions of the cathode microstructure and correlated the obtained partial conductivities with microstructural descriptors such as tortuosity factors, identifying possible kinetic bottlenecks. We found that minimizing residual porosity, which blocks ion and electron transport, is necessary to optimize cathode microstructures and enhance ASSB performance. Moreover, high-performance anodes, along with protective concepts, are crucial for establishing dense, high-energy ASSB cells. Lithium metal anodes may not be the ultimate solution, and silicon anodes can pose advantages, e. g. in terms of electrochemical stability for thiophosphate separators. Discussion: Our studies demonstrate the importance of optimizing the microstructure of cathodes and carefully designing Si anodes for improved ASSB cells. By manipulating the particle size distribution of the solid electrolyte, we achieved more efficient electronic and ionic transport pathways, leading to improved battery performance. The presented work is primarily published in references 1-5, detailing key challenges and showcasing optimization strategies for these topics. Beyond that, diversity in materials, research teams, and approaches is crucial for long-term successful development of ASSB. Acknowledgement: Scientific and administrative coordination of the BMBF Competence Cluster for Solid-State Batteries (FestBatt), FB2-Koord (03XP0431), and cell platform Thiophosphates, FB2-Thio (03XP0430A).

Electrifying the automotive sector requires energy storage systems with high energy and power density, intrinsic safety, and long durability.[1] Lithium-based all-solid-state batteries (ASSBs) are considered promising next-generation energy storage devices, as they possibly meet these requirements by replacing organic liquid electrolytes with non-flammable solid electrolytes (SEs) and by enabling the application of novel high energy density anode concepts.[2, 3] Among the SE material classes being pursued for use in ASSBs, sulfidic systems are considered particularly advantageous, as they possess high ionic conductivities and low Young’s moduli, enabling easier processing and densification compared to oxidic systems.[4] However, a rarely addressed key bottleneck to commercializing ASSBs with sulfidic SEs is the requirement on the environmental conditions during handling, processing, and assembly of the battery components, which will be dictated by the instability of sulfidic SEs towards humidity.[5] On the laboratory scale, this issue has been avoided by handling the sulfidic ASSB materials, components, and cells in argon-filled gloveboxes, but for the commercial production of ASSBs their manufacturing would preferably be done in a dry-room atmosphere.[6] However, very few studies exist that examine whether the dew points of typical dry-rooms are sufficient to handle and/or store ASSB components based on sulfidic SEs.[7,8] In this contribution, we will examine the dry-room compatibility of scalable sulfidic composite (Li6PS5Cl/HNBR) sheet-type separators,[9] investigating the influence of the exposure time to a dry-room atmosphere with a dew point of -48°C on the stability of the SE and on its electrochemical properties. Using X-ray diffraction (XRD) combined with Rietveld refinement and scanning electron microscopy (SEM), the influence on the morphology and the formation of degradation products upon reaction with the small concentration of water in a dry-room will be investigated. The results show that only long exposure times (> 96 h) lead to a significant hydrolysis-induced change in the XRD diffractograms, which indicates the formation of degradation products such as Li2S, LiCl, and Li3PO4.By means of potential electrochemical impedance spectroscopy (PEIS), the impact of different exposure times on the Li+-ion conductivity of the sheet-type Li6PS5Cl/HNBR separators and the activation energy for the Li+-ion transport are investigated (cf. figure 1). While short exposure times (< 12 h) have a minor influence on the Li+-ion conductivity (lowering it from 0.3 mS/cm to 0.25 mS/cm) and a negligible effect on the activation energy, longer exposure times (> 48 h) lead to a ≈ 10-fold loss of ionic conductivity (to ≈ 0.03 mS/cm) and a drastic increase in activation energy.Besides measuring the loss of ionic conductivity, the separator sheets are also used for assembling LiNi0.6Co0.2Mn0.2O2|LiIn half-cells, which are investigated using galvanostatic cycling. An analysis of the capacity profiles shows that an increased exposure of the separators to the dry-room atmosphere leads to a significant IR-drop, to lower initial discharge capacity, and enhanced capacity fading over several charge/discharge cycles. Further insights into these degradation phenomena will be gained by analyzing the dQ/dV plots, the mean (dis)charge voltage, and the full-cell impedance of the half-cells.Based on our findings, it can be concluded that moderate exposure times in a dry-room of up to 12 h have only a negligible effect on the chemical integrity and performance of sulfidic Li6PS5Cl/HNBR separators sheets. This opens the route of defining viable storage and processing times of sulfidic ASSBs cell components in industrial dry-room environments.[1] Y. Ding, Z. P. Cano, A. Yu, J. Lu, Z. Chen, Electrochemical Energy Reviews, 2, 1 – 28, (2019).[2] J. Janek and W. G. Zeier, Nature Energy, 1, 16141, (2016).[3] P. Oh, J. Yun, J. H. Choi, K. S. Saqib, T. J. Embleton, S. Park, C. Lee, J. Ali, K. Ko, J. Cho, Angew. Chem. Int. Ed., 61, e202201249, (2022).[4] A. Sakuda, A. Hayashi, M. Tatsumisago, Scientific Reports, 3, 2261, (2013).[5] H. Muramatsu, A. Hayashi, T. Ohtomo, S. Hama, M. Tatsumisago, Solid State Ionics, 182, 116 – 119, (2011).[6] D. H. S. Tan, Y. S. Meng, J. Jang, Joule, 6, 1755-1769, (2022).[7] Y.-T. Chen, M. A. T. Marple, D. H. S. Tan, S.-Y. Ham, B. Sayahpour, W.-K. Li, H. Yang, J. B. Lee, H. J. Hah, E. A. Wu, J.M. Doux, J. Jang, P. Ridley, A. Cronk, G. Deysher, Z. Chen, Y. S. Meng, J. Mater. Chem. A , 10, 7155-7164, (2022).[8] C. Singer, H.-C. Töpper, T. Kutsch, R. Schuster, R. Koerver, R. Daub, ACS Appl. Mater. Interfaces, 14, 24245–24254, (2022).[9] C. Sedlmeier, T. Kutsch, R. Schuster, L. Hartmann, R. Bublitz, M. Tominac, M. Bohn, H. A. Gasteiger, J. Electrochem. Soc., 169, 070508, (2022). Figure 1

<p indent="0mm">Since the commercialization of lithium-ion batteries in the 1990s, lithium-ion batteries have been successfully applied in portable electronics, electric vehicles, and grid energy storage. Although current organic liquid electrolytes have high ionic conductivities, they are inherently flammable, volatile, and prone to leakage. Moreover, severe side reactions and dendrite growth on the surface of the lithium anode during the charge-discharge process can cause safety hazards, which greatly impede their applications in lithium metal batteries. Solid electrolytes, including inorganic solid electrolytes and polymer electrolytes, are regarded as effective alternatives to organic liquid electrolytes for the construction of lithium metal batteries with high energy density and safety. Among them, solid polymer electrolytes offer excellent flexibility, processability, and interfacial compatibility over inorganic solid electrolytes, and they are extraordinarily promising for lithium metal batteries with high energy density and safety. Ideal solid polymer electrolytes should have following features: (1) High ionic conductivity (&gt; <sc>10 ^–4 S cm ^–1) </sc> at room temperature; (2) high lithium ion transference number (~1) to reduce the concentration polarization and improve the rate performance of batteries; (3) intimate contact at the electrode/electrolyte interfaces; (4) wide electrochemical window <sc>(&gt;4.5 V</sc> vs. Li/Li ⁺) to match high-voltage cathodes and improve the energy density of batteries; (5) good mechanical stability to resist processing, buffer electrode volume change and inhibit dendrite growth; (6) good thermal stability to withstand environmental changes. Generally, the ionic conductivity of pure solid polymer electrolytes at room temperature is low <sc>(~10 ^–6 S cm ^–1). </sc> Researchers have tried to improve the ionic conductivities by adjusting the lithium salt concentration, such as developing “polymer-in-salt” solid electrolytes. However, increasing the concentration of lithium salt leads to the deterioration of the mechanical strength. Strategies such as developing novel lithium salts, modifying polymer matrix, and incorporating inorganic fillers into solid polymer electrolytes are proposed to promote ionic conductivities of solid polymer electrolytes. In particular, composite polymer electrolytes, fabricated by dispersing a certain amount of inorganic fillers into solid polymer electrolytes, have improved ionic conductivities without sacrificing their mechanical performances. Poor interfacial property between electrodes and electrolytes is also a critical issue for solid polymer electrolytes. On one hand, poor and uneven solid/solid contacts at the electrode/electrolyte interfaces lead to high resistance and sluggish ionic transport kinetics. Furthermore, the volume change of the positive and negative electrodes in the charge/discharge process deteriorates the interfacial contacts, blocks the ion and electron transport through the interfaces, and greatly reduces the electrochemical reaction kinetics. On the other hand, the electrochemical windows of solid polymer electrolytes are usually narrow <sc>(＜4.5 V).</sc> During cycling, redox reactions are prone to occur at the electrode/electrolyte interfaces, causing battery failure. Solid polymer electrolytes have also poor thermal and mechanical stabilities. Therefore, design and synthesis of polymer-based solid electrolytes with excellent comprehensive performances and construction of fast and stable ion transport channels at the electrolyte/electrode interfaces are of great significance for the successful development of solid-state lithium metal batteries. This paper presents a brief review of the research progress in solid polymer electrolytes from two aspects: Improving the ionic conductivities of solid polymer electrolytes and enhancing the interfacial performance at electrolyte/electrode interfaces. First, targeted optimization strategies on ionic conductivities of solid polymer electrolytes, including constructing continuously aligned ionic transport paths and shortening the ionic transport distance, are summarized. Second, interface optimization strategies, including constructing wetting interfaces and synthesizing asymmetric electrolytes, are presented to reduce the interface resistance and improve the interfacial contact. Finally, perspectives on the development of solid polymer electrolytes and high-performance solid-state lithium metal batteries are discussed, and key research directions and advanced test methods are proposed. This review may provide a comprehensive understanding and further guidance for not only the material design of solid polymer electrolytes, but also the structural design of lithium metal batteries with favorable electrochemical and interfacial performances.

Innovation in the design of Li-ion rechargeable batteries is necessary to overcome safety concerns and meet energy demands. In this regard, a new generation of Li-ion batteries (LIBs) in the form of all-solid-state batteries (ASSBs) has been developed, attracting a great deal of attention for their high-energy density and excellent mechanical-electrochemical stability. This review describes the current state of research and development on ASSB technology. To this end, study of the literature and patents as well as market analysis over the last two decades were carried out, highlighting how scientific achievements have informed the application of commercially profitable ASSBs. Analyzing the patents registered over the past 20 years revealed that the number of them had increased exponentially-from only few per year in early 2000 to more than 342 in 2020. Published literature and patents on the topic declare a solid-state electrolyte (SSE) to be the main component of ASSBs, and most patented examples are referred to as solid inorganic electrolytes (SIEs), followed by solid polymer electrolytes (SPEs) and solid hybrid electrolytes (SHEs) in popularity. Investigation of company websites, social media profiles, reports, and academic publications identified 93 companies associated with ASSBs. A list of leading businesses in the solid-state battery sector was compiled, out of which 36 provided information on the ASSB units in their product portfolio for detailed analysis.

For the growth of electric vehicle market, lithium-ion batteries (LIBS) used in the EVs still requires safety and reliability. Unfortunately, large-scale application of the LIBs is being challenged due to the fact that the use of flammable liquid electrolytes has caused safety issues such as leakage and fire explosion. In this respect, all-solid-state batteries (ASSBs) have been intensively studied to ensure the safety and mileage that are superior to the current LIBs. In terms of solid electrolytes, oxide electrolytes not only shows high ionic conductivity (10-4 ~ 10-3 S/cm) but also high mechanical strength to suppress surface dendrite formation. In addition, the oxide electrolytes possess advantages such as non-flammability, high thermal stability, and excellent electrochemical stability (~ 6 V), enabling high temperature/high voltage operations of oxide-based ASSBs. However, most of oxide materials require a sintering process at high temperatures to form a planar solid electrolyte. And a lack of flexibility results in non-uniform electrolyte/electrode contact in the battery, which makes it difficult to apply the rigid oxide electrolyte directly. On the other hand, solid polymer electrolytes have also been actively investigated due to no leakage, good electrolyte/electrode contact, easy processing, flexibility, and good film formability. However, the solid polymer electrolytes have critical disadvantages such as low ionic conductivity at room temperature and low thermal/mechanical stability, which precludes commercialization of solid polymer-based ASSBs despite their advantages. To overcome each disadvantages of oxide and polymer electrolytes, we developed hybrid electrolytes for improved ionic conductivity, easy processing, and formation of continuous electrolyte/electrode interface. In this presentation, pragmatic approach and current challenges related to solid batteries will be discussed including innovative manufacturing process. Hybrid electrolytes and their synergistic effect on the battery performance as a promissing solution will be presented [Fig. 1]

Inorganic solid electrolytes are one of the key materials instead of organic liquid electrolytes for next-generation all-solid-state batteries (ASSBs). The advantages of ASSBs are long cycle life and high safety due to the non-flammable of the solid electrolyte. The ASSBs can be stacked layer by layer, reducing the volume in battery packaging and resulting in increased energy density. These ASSBs can be applied to wearable or healthcare or smart home devices in the form of multilayer ceramic battery (MLCB), in addition to energy storage devices and electric vehicles. However, the MLCBs are difficult to fabricate due to the high sintering temperature and high interfacial resistance of the solid electrolyte. The Li-based solid electrolytes of NASICON-type have received much attention as prospective solid electrolytes due to their high ionic conductivity and high stability against moisture. Especially, lithium aluminum germanium phosphate (LAGP) is potential solid electrolyte material in the NASICON family due to superior stability. LAGP glass electrolyte was selected to enable sintering at low temperatures and reduce resistance at the interface for the application to MLCB.In this study, a LAGP-based solid electrolyte ceramic sheet was prepared using glass/powder composite at 750 °C. The obtained LAGP-based solid electrolyte exhibited a NASICON-type hexagonal structure and a total ionic conductivity of 1.45 × 10-4 S/cm at 25 ˚C. A Coin cell with the LAGP composite electrolyte, LiCoO2 (LCO) as cathode, and Li metal as anode was assembled. The coin cell was charged and discharged by using a battery cycler and the charge capacity was approximately 130 mAh∙g-1. Additionally, we prepared a LiMnPO4 glass-based cathode (LMP) using conventional melt quenching techniques and then stacked it layer by layer with the LAGP electrolyte and co-sintered at 650°C. After co-sintering the LAGP/LMP cell, it was confirmed that the interface between the LAGP composite electrolyte and the LMP cathode was well attached, and its ionic conductivity maintained a value similar to that of the LAGP composite electrolyte. Subsequently, an electrochemical analysis of the LAGP/LMP cell was performed.

Lithium-ion batteries have high capacity and energy density, but there is a problem in terms of safety because an organic electrolyte solution is flammable. Therefore, development of large-scale lithium-ion batteries with high safety is a challenge for practical use. All-solid-state batteries are attracting attention because they use non-flammable inorganic solid electrolytes. In particular, all-solid-state batteries using metal anode have been expected to be next-generation rechargeable batteries because of their high-energy density using metal anode. Nevertheless, they have not yet been used because metal dendrites cause short circuits during charge and discharge processes. Metal dendrites grow along grain boundaries in polycrystalline solid electrolytes.1) However, there is no report on direct observation of dendritic growth in amorphous solid electrolytes without grain boundaries. To elucidate the mechanism of dendrite formation in solid glass electrolytes, we observed direct three-dimensional images during electrochemical reactions of all-solid-state cell by using operando X-ray computed tomography (CT) with synchrotron radiation. Although lithium metal is generally used as anode, such a light element is difficult to be detected using X-ray absorption techniques. In this study, as a model case of dendrite formation in all-solid-state batteries using metal anode, a battery cell using silver-ion solid electrolytes was examined. Silver-ion conductors have the advantage that their solid electrolytes exhibit high conductivity at room temperature.2) 3) Also, the variation of glass composition is enough, which makes easy to design the battery cell for X-ray CT measurement. Study on silver-based glass electrolytes is mainly being proceeded on oxide-based and sulfide-based materials. Among them, AgI-Ag2O-P2O5 glass electrolyte was selected because it has high flexibility in composition and high chemical stability in air.4) AgI, Ag2O, and P2O5 were mixed at mole ratio of 1:1:1. The mixed powder was calcined at 520 °C for 2 hours. After that, glass electrolyte was obtained by quenching AgI-Ag2O-P2O5 melt to room temperature. X-ray diffraction measurements of the synthesized material revealed the amorphous phase. In this study, a vacuum pump and a quartz glass tube with an inner diameter of 0.24 mm were used to mold the glass electrolyte. First, AgI-Ag2O-P2O5 melt was quenched in a quartz glass tube. Second, an electrode material prepared by mixing silver and AgI-Ag2O-P2O5 glass powder at a mass ratio of 3:1 was added from both ends of the glass tube. Finally, a titanium wire with a diameter of 0.20 mm was connected to the electrode. In this way, we prepared Ag |AgI-Ag2O-P2O5| Ag cell in a diameter of 0.24 mm. Micro-X-ray CT measurements were performed at BL20XU in Spring-8. The X-ray energy was 20 keV. The CT scans were performed before and after the chronopotentiometry measurement.Before the electrochemical measurement, the observed CT images showed the micro-cracks in the glass solid electrolyte. After the chronopotentiometry measurement, it was confirmed that silver metal grew from the point of the initially presented crack. Also, the crack expanded based on the presented crack. It means that the silver metal formation induces additional cracks. The CT images obtained before and after the chronopotentiometry measurement indicate that the silver metal dendrite formation causes the stress in the solid electrolyte, resulting in additional crack formation.1) R. Sudo, Y. Nakata, K. Ishiguro, M. Matsui, A. Hirano, Y. Takeda, O. Yamamoto and N. Imanishi, Solid State Ionics, 262, 151 (2014).2) J. C. Burbano, J. E. Diosa, and D. Peña Lara, Molecular Simulation 45, 724-727 (2019).3) T. Takahashi, S. Ikeda, and O.Yamamoto, J. Electrochem. Soc. 120, 647 (1973).4) M. Tatsumisago and A. Hayashi, J. Chem. Soc. 35, 3 (2006).

All-solid-state batteries (ASSBs) are promising candidates for application as next-generation high-power supply and storage devices in electric vehicles. ASSBs offer excellent safety and a high energy density; however, the high interfacial resistance between the positive electrode and solid electrolyte due to solid–solid contact reactions at elevated temperatures limits their applications. To address these issues, the effect of thermal annealing on the interfacial structure between a sodium super ionic conductor (NASICON)-type Li1.3Al0.3Ti1.7(PO4)3 (LATP) solid electrolyte and a LiCoO2 (LCO) cathode in an ASSB fabricated by aerosol deposition was investigated experimentally. Specifically, spectrum imaging was conducted by combining scanning transmission electron microscopy and electron energy loss spectroscopy. Metastable degraded low-density transition layers were formed between LATP and LCO in the as-deposited sample. A significant reduction in interfacial resistance was achieved after thermal annealing at 250–300 °C, which was mainly attributed to structural recovery in this temperature range. However, thermal annealing at 400 °C resulted in increased interfacial resistance due to the formation of a Co3O4-like spinel blocking layer at the LATP/LCO interface. These findings provided valuable insights into the electronic properties of the ASSB composite under investigation and were consistent with theoretical predictions of Li and O transfer between the layers due to thermal annealing.

There is a growing interest in the sustainability of the aviation industry sector over the past years due to the environmental issues associated with traditional aviation engines. Electric and hybrid aircrafts are considered promising technologies for reducing fuel consumption and enhancing system efficiency [1]. However, electrical energy storage systems require a higher capacity-to-weight ratio than today’s Li-ion batteries to fulfil the high demands in this area. Safety restrictions imposed by liquid electrolytes motivate the development of next-generation chemistries, such as oxide-based all-solid-state batteries (ASSB) for aviation, which have non-flammable electrolytes [2]. This option is investigated in the context of the IMOTHEP European project that aims at identifying promising hybrid aircraft configurations and studying the associated technology. However, the major drawbacks of oxide-based solid electrolytes are weak contact between electrode and electrolyte interface, low mechanical flexibility, and high density, which limit their use for high gravimetric energy density applications. To mitigate the aforementioned concerns, the solid polymer composite electrolytes approach could be applied, where oxides are mixed with polymer electrolytes [3].Designing an optimum cell without ion transport limitations using experimental investigations is time- as well as resource-intensive due to the large number of iterations in production and evaluation required to achieve a well-performing design. Physics-based modelling is able to create a platform that can directly assess the impact of cell structure on battery performance and provide knowledge concerning limiting processes within the cell. Therefore, we here present the first study that combines a pseudo-two-dimensional model for the model-assisted evaluation of Li-ASSB with various hybrid electrolytes and single-ion conductor electrolytes with an evolutionary algorithm to identify optimum cell designs to reach a higher gravimetric energy density (see Fig. 1-a). To this end, we first compared the performance of several hybrid electrolytes with their experimental properties, to identify which electrolyte performs well with present technology and which has the potential to become an attractive alternative in the future.Our findings reveal that based on available ASSB technology, single ion-conducting electrolytes cannot achieve a higher gravimetric energy density than hybrid electrolytes at low current rates due to their high density, as shown in Fig. 1-b. ASSB based on 12.7 vol% of garnet Li6.4La3Zr1.4Ta0.6O12 (LLZTO) is the best option based on present manufacturing constraints. Furthermore, our study revealed that hybrid electrolytes based on 10 wt% of Li1.3Al0.3Ti1.7(PO4)3 (LATP) could be promising for future aircraft if researchers succeed to decrease its electrolyte thickness and chemical stability in contact with lithium metal anode. Further, sensitivity analyses enabled us to identify that the cathode thickness and volume fraction of cathode materials are critical parameters for the cell design of ASSB. Therefore, we applied a global optimisation to enhance gravimetric energy density by changing these two electrode design parameters. After optimisation, gravimetric and volumetric energy densities of 618 Wh kg-1 and 1251 Wh L-1 for 0.1C discharge are achieved, respectively, indicating that the cell with the optimal electrode design could meet the mission demand in the aviation industry with a gravimetric energy density of 500 Wh kg-1 and volumetric energy density of 1000 Wh L-1.In conclusion, the findings of this study show that our physics-based modelling in conjunction with an optimisation algorithm predicts the optimal composition of ASSB for a given constraint and thus supports the time- and cost-effective development of batteries that fulfil mission requirements, e.g. in the aviation sector.This work is conducted in the frame of the project IMOTHEP (Investigation and Maturation of Technologies for Hybrid Electric Propulsion), which has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No 875006 IMOTHEP.

Introduction All-solid-state batteries (ASSBs) utilize non-flammable solid electrolytes, offering enhanced safety. In addition, the application of lithium metal anodes is expected to further improve energy density. Among solid electrolytes, oxide-based solid electrolytes have attracted increasing attention due to their higher stability under atmospheric conditions compared to sulfide-based solid electrolytes. However, oxide-based solid electrolytes exhibit lower ionic conductivity compared to sulfide-based and liquid electrolytes, leading to inferior performance on high-rate cycling.We focused on a novel oxide-based solid electrolyte, lithium lanthanum niobium oxyfluoride (Li1.25La0.58Nb2O6F, LLNOF) [1], which has a bulk ionic conductivity of 7 mS cm-1, which is the highest among oxide-based solid electrolytes reported so far. However, the electrolyte with a high relative density is difficult to be prepared, and the residual voids in the electrolyte easily allow lithium dendrite formation, leading to short circuits. Consequently, improving the sintered density remains an important issue for the LLNOF electrolyte to be used in practical cells. We have reported that the co-addition of alumina (Al2O3) [2] and lithium tungstate (Li2WO4) [3] as sintering aids increased the relative density of lithium lanthanum zirconium tantalate (Li6.4La3Zr1.4Ta0.6O12, LLZT) [4]. In this study, we investigated the effects of various sintering aids on the densification and ionic conductivity of the LLNOF electrolyte. Experimental LLNOF powder used in this experiment was provided by DENSO Corporation [1]. Sintering aids such as Li2WO4, Al2O3, Li2ZrO3, Li2MoO4, and Li2.2C0.8B0.2O3 (LBCO)[5] were used, with each added at 2 wt.%. The LLNOF powder and sintering aids were mixed using a planetary ball mill. A powder of 0.5 g was then pressed into a green pellet at 98 MPa. The green pellet was wrapped in copper foil and sintered at 1000 ℃ for 6 h under Ar atmosphere. The sintered pellet was dry polished to adjust the thickness at 1.0 mm, and Au blocking electrodes were sputtered on both sides of the pellet for conductivity measurements. AC impedance measurements were performed at an applied voltage of 10 mV over the frequency range from 7 MHz to 1 Hz in the temperature range 60 to -20°C. Results and Discussion Table 1 summarizes the relative density, ionic conductivity, and lattice parameters of LLNOF electrolytes with and without sintering aids. The highest relative density (92.7%) was obtained when Li2WO4 was added. However, the bulk ionic conductivity decreased to 2.73 mS cm-1, which was lower than that of LLNOF without sintering aids. The increase in relative density can be attributed to the fact that Li2WO4 has a melting point (742°C) lower than the sintering temperature, leading to the formation of a liquid phase that enhances sintering density.Figure 1 shows the relationship between lattice parameters and ionic conductivity. The ionic conductivity decreased with a decrease in the lattice parameter except for Li2ZrO3. The highest ionic conductivity was observed for the sample prepared without sintering aids. This can be attributed to elemental substitution within LLNOF caused by the addition of sintering aids. Figure 2 shows the cross-sectional SEM images of LLNOF pellets. The pellets prepared with Li2WO4 and LBCO, which generate a liquid phase, exhibit relatively larger grain sizes and fewer voids, resulting in higher relative densities. On the other hand, the sample with Al2O3 has a relatively higher number of residual pores within the grains, which is considered to have led to a decrease in relative density. These results suggest that liquid-phase sintering facilitates the densification of LLNOF.

Lithium-ion batteries (LIBs) have played a pivotal role in advancing energy storage technologies, enabling high-demand applications such as electric vehicles and renewable energy storage systems. Despite their widespread use, LIBs face significant challenges in terms of energy density and intrinsic safety issues. These challenges have spurred interest in all-solid-state batteries (ASSBs), which utilize solid electrolytes (SEs) to offer safe alternatives to conventional liquid electrolyte-based LIBs. Among the various types of SEs explored to date, halide SEs exhibit improved compatibility with high-voltage oxide cathodes, as compared with sulfide-based SEs. Thus, halide SEs may be utilized as cathode coating materials for ASSBs using sulfide SEs with high ionic conductivity. However, the specific material properties that determine the chemical/electrochemical characteristics of halide coatings have not been clearly studied yet.In this study, we synthesize lithium yttrium chloride (Li3YCl6, LYC) SEs using different methods (solid-state synthesis and ammonium-assisted liquid-phase synthesis) at various heat-treatment temperatures to control phase compositions and crystal structures. These allow us to systematically explore the phase-structure-property relationship of LYC SEs and their roles as coating materials for LiNi0.90Co0.05Mn0.05O2 (NCM). Our experimental findings reveal that the phase, crystal structure and crystallinity of LYC significantly influence the microstructure, ionic conductivity, interfacial compatibility, and thermal stability of LYC-coated NCM (NCM@LYC). The crystal structure and crystallinity of synthesized LYC SEs are explored by Rietveld refinement of X-ray diffraction patterns. Notably, LYC SEs prepared via wet synthesis under optimal heat-treatment conditions exhibit superior Li-ion transport kinetics due to the enhanced crystallinity of phase-pure LYC. This leads to the improved interfacial resistances of NCM@LYC, as evidenced by impedance analyses of NCM composite electrodes. Therefore, the NCM@LYC composite electrodes with the optimized LYC SE show significant improvement in rate capability and cycle lifetimes. This research elucidates the critical role of the synthesis conditions in controlling the properties of halide coating materials and thus in improving the interfacial kinetics and stability of composite cathodes of ASSBs. The insights gained from the phase-structure-property relationships provide valuable guidelines for the development of highly conductive and stable SEs for next-generation batteries.

Enabling stable and high areal capacity solid state battery with Ni-rich cathode via failure mechanism study