Lithium-Graphite Paste: An Interface Compatible Anode for Solid-State Batteries.

Lithium-ion batteries (LIBs) are widely used in a variety of applications due to their high energy and power densities, and long cycle life. With the expanding use of LIBs in electric vehicles and energy storage systems, there is very active research into all-solid-state batteries (ASSBs), which offer greater energy density than traditional LIBs and eliminate the inherent fire hazards. Since most of the detailed reactions involved in the performance and degradation of a battery are temperature-sensitive, so-called thermal activation processes, it is very important to accurately assess whether a battery can have the high performance and low degradation characteristics required under different climatic conditions. To evaluate the electrochemical properties of electrode materials in LIBs, a half-cell is typically constructed with the electrode of interest as the working electrode (WE) and lithium metal as auxiliary electrode (AE). Here, lithium metal is close to an ideal non-polarizable material, has a large capacity, and maintains a constant potential during charge/discharge, so it is widely used as AE material in LIB research. However, several issues arise when lithium is used as AE in ASSBs: Lithium metal undergoes mechanical deformation due to the relatively high internal pressure required to ensure good contact between lithium and solid electrolyte; When in contact with sulfide-based solid electrolytes, which are currently of interest due to their high ionic conductivity, side reaction products can lead to an increase in interfacial resistance; the growth of lithium dendrites, often observed in conventional LIBs, is still unavoidable. These issues all affect the half-cell signal, potentially causing a distorted evaluation of the WE’s characteristics.Lithium-indium alloy is being utilized as AE for ASSB half-cells to replace lithium metal. It exhibits excellent mechanical ductility and maintains a constant reduction potential over a wide stoichiometric range, ensuring excellent contact property and voltage stability. Moreover, it is very easy to fabricate through simple compression at room temperature. Nevertheless, the limited study on its electrochemical properties leaves uncertainty regarding its full functionality as AE for accurate evaluation of WE, particularly in extreme operational conditions. For instance, lithium-indium alloy are primarily based on alloying/dealloying reactions involving solid-state diffusion of lithium, which is generally considered to be a relatively slow process kinetically, while lithium only involves a kinetically favorable plating/stripping process on the surface. Therefore, a comparative analysis of these different reaction mechanisms in terms of kinetics is necessary. This presentation presents a comparative analysis of the electrochemical properties of lithium metal and lithium-indium alloys used as AEs in ASSB half-cells. In particular, the electrochemical properties of lithium-indium alloys with different reaction mechanisms with lithium are investigated over a range of temperatures and current densities, and these differences are discussed from a kinetic point of view. For this purpose, first, using a three-electrode half-cell with lithium or lithium-indium alloy as AE, we compared the electrochemical properties of these two AEs during half-cell operation by interpreting their potential and over-potential changes, and quantifying their detailed resistances. Then, through dc experiments on lithium and lithium-indium symmetrical cells, we identified differences in overvoltage behavior due to differences in their reaction mechanism. In particular, we noted distinct differences in the overpotential behavior of these two electrodes at low temperatures and high current densities. Furthermore, based on the results of a combined dc/ac electrochemical analysis, we derived the overvoltage that dominates the overall overvoltage at each of the two electrodes. Based on these results, we analyzed how the kinetic differences between the two electrodes affect the cathode half-cell signal, in order to derive key considerations for reliable ASSB half-cell evaluation. In this presentation, the advantages and disadvantages of lithium-indium alloy compared to lithium metal as AE will be discussed from a kinetic perspective, focusing on interfacial and bulk resistance (overpotential). Furthermore, methods for utilizing AE to conduct accurate and reliable half-cell tests will be proposed.

While conventional lithium-ion batteries (LIBs) continue to gain progress through incremental improvements, the presence of organic liquid electrolytes brings about fundamental safety issues as their reactivity and flammability subject LIBs to thermal runaway. [1-4] With higher energy densities and better safety performances, all-solid-state batteries (ASSBs) consisting of a 4 V-class cathode active material (CAM), an inorganic solid-state electrolyte (SE) and a lithium-metal anode are considered the future of energy storage technologies. [5-6] The development of practical ASSBs, however, has met a number of challenges. SEs simultaneously meeting the criteria in conductivity, stability and mechanical properties are yet to be discovered. At the anode, reductive degradation of SE, high interfacial impedance and dendrite formation are the most pressing issues. At the cathode, instabilities due to oxidative degradation of SE, reactivities between SE and CAM as well as the loss of mechanical integrity significantly limit ASSB performance.In this presentation, we discuss our recent effort in addressing these challenges, including the development of novel halide SEs, design of composite cathode structure that enables direct use of uncoated-LiNi0.8Co0.1Mn0.1O2 CAM, and implement of Li-metal based anodes that enable better interface with the SE. We demonstrate the excellent long-term cycling performance achieved on such cells and illustrate the underlying working mechanism. [7] The importance in proper matching of cathode, SE and anode properties as well as our views on future development of better-performing ASSB cells will be presented. References Arbizzani, G. Gabrielli and M. Mastragostino, Journal of Power Sources, 2011, 196, 4801-4805.Murmann, R. Schmitz, S. Nowak, N. Ignatiev, P. Sartori, I. Cekic-Laskovic and M. Winter, Journal of The Electrochemical Society, 2015, 162, A1738.Cao, X. Ren, L. Zou, M. H. Engelhard, W. Huang, H. Wang, B. E. Matthews, H. Lee, C. Niu and B. W. Arey, Nature Energy, 2019, 4, 796-805.Fan, L. Chen, O. Borodin, X. Ji, J. Chen, S. Hou, T. Deng, J. Zheng, C. Yang, S.-C. Liou, K. Amine, K. Xu and C. Wang, Nature Nanotechnology, 2018, 13, 715-722.Janek and W. G. J. N. E. Zeier, Nature Energy, 2016, 1, 1-4.Famprikis, P. Canepa, J. A. Dawson, M. S. Islam and C. Masquelier, Nature Materials, 2019, 18, 1278-1291.Y. Kim, H. Cha, R. Kostecki and G. Chen, ACS Energy Letters 2023, 8, 521.

Garnet-type Li7La3Zr2O12 (LLZO) Solid-State Electrolytes (SSEs) enable Solid-State Lithium Metal Batteries (SSLMBs) with high power density due to their superior ionic conductivity over 1 mS cm-1 at room temperature and good chemical stability against Lithium (Li) metal. A major cause of failure in SSLMBs is the large interfacial resistance between LLZO and electrodes. The high resistance at the interfaces is normally associated with insufficient solid-solid surface contact. It is a common practice to introduce a Liquid Electrolyte (LE) in SSLMBs either in combination with SSEs to form quasi-solid electrolytes or as the interface to enhance battery cycling performance. Several studies are conducted on resolving the contact issue between LLZO and the Li-metal anode but very few focused on the LLZO/cathode interface.In this research, a carbonate-based LE was introduced at the interface of Li6.5La2.9Ba0.1Zr1.4Ta0.6O12 (LLBZTO) | LiNi0.6Mn0.6Co0.2O2 (NMC 622) cathode with the aim of understanding the mechanism which the LE enhances the SSLMBs performance, using the Scanning Transmission X-ray Microscopy (STXM) and X-ray Absorption Scanning (XAS). The assembled Li | LLBZTO SSEs | LE | NMC 622 cell exhibited an initial discharge capacity of 168 mAh g-1 with a capacity retention ratio of ~82 % after 30 cycles. The results from the STXM revealed the reactions of the LE with LLZO and NMC 622. The XAS analysis showed the formation of two new interfaces: Cathode-Electrolyte Interface (CEI) and Solid-Liquid Electrolyte Interface (SLEI). Also, the result indicated that the LE decomposed completely in the cell after 30 cycles and transformed to a dense and robust SLEI. This in turn led to the enhanced interfacial contact with the cathode and an improved Li+ ion transport at the interface. In addition, fluorides (i.e., LiF and LaF3) and carbonates (i.e., Li2CO3) were confirmed as the main components of the SLEI. In this study, two interfaces in SSLMBs (CEI and SLEI) were characterized. Fully understanding the roles of LE as the interface would enhance the practical application of quasi-solid electrolytes in SSLMBs. Keywords Solid-state lithium metal batteries; Garnet; Interface; Ceramic electrolyte; STXM

All-solid-state batteries (ASSBs) are one of the most promising next-generation energy storage strategies that combine large energy with safety and stability. Critically, replacing liquid electrolytes with superionic solid-state electrolytes (SSEs) helps to overcome central challenges associated with conventional lithium-ion batteries, such as flammability, electrochemical compatibility, and active-material crossover. Realizing ASSBs with large energy density in practical configurations relies on the efficient use of both anodes with large capacity (e.g., alkali metals, alloys) and state-of-the-art cathodes (e.g., oxide insertion hosts, conversion chemistry) in composite microstructures with large areal capacity. Further, advancements of sustainable sodium (Na) ASSBs are projected to enable volumetric energy density competitive for stationary storage applications (~ 700 Wh·L-1) with low cost (< $50 kWh-1). However, various challenges, such as electro-chemo-mechanical degradation at SSE/cathode/anode interfaces, has restricted implementation of ASSBs to date. Despite these challenges, innovations in fundamental materials chemistry, full-cell fabrication approaches, and scalable manufacturing routes continue to advance the achievable performance of ASSBs. Here, we will offer a perspective on trends in materials design for the most promising classes of sodium SSEs and showcase recent results from Prof. Shirley Meng’s Laboratory for Energy Storage and Conversion (LESC), including the discovery of new SSEs and design principles for enabling anode-free sodium ASSBs.

The correlation between the electrochemical performance and the electronic structure and chemical composition of the cathode/electrolyte-and anode/electrolyte-interfaces in all-solid-state batteries (ASSB) is systematically studied. ASSBs are composed of LiCoPO4 (LCP) or LiCoO2 (redox potential ~4.8 V and ~3.8 V vs Li+ /Li, respectively) thin-film cathode materials, Li1+xAlxTi2-x(PO4)3 (LATP) as the solid-state electrolyte and lithium metal as the anode. X-ray photoelectron spectroscopy (XPS) interface experiments on LCP thin-film deposition on the LATP surface reveal a partial reduction of Ti4+ ions attributed to electronic charge transfer from LCP to LATP without the involvement of the PO4 polyanion in the process. Electrochemical activity of the ASSBs is primarily limited by the anode/electrolyte interface rather than the cathode/electrolyte interface. Post-cycling XPS analysis of the Li∣LATP interface indicates lateral and in-depth chemical inhomogeneity with a strong change in PO4 polyanionic chemical environment and Li+ accumulation at the areas with a better electrolyte/anode contact. Engineering the Li∣LATP interface via coating of the LATP surface with lithium oxynitride (LiPON) or a LiTFSI-PEO polymer electrolyte, or by wetting the LATP with the liquid electrolytes, significantly improves battery cycling stability even without artificial interface modification at the cathode side. The optimized Li∣LiTFSI-PEO∣LATP∣LCP cells showed excellent cycling performance between 3.0 V and 5.0 V at a charging time of 12 min (≈ 5C rate). Stable cycling was sustained over 10 cycles, followed by 30 and 50 additional cycles at reduced charging rates (≈ 4C and 1C, respectively). Good electrochemical cyclability was further demonstrated with an upper cut-off voltage of 5.3 V vs. Li+ /Li.

Currently, the so-called all-solid-state battery (ASSB) is getting enormous attention in academia and industry as a potential next-generation battery technology replacing the state-of-the-art lithium ion battery (LIB) based on a liquid electrolyte. Especially the high energy density (Wh/L) and specific energy (Wh/kg) are appealing [1] with regard to the application in electric vehicles and protable devices. However, the breakthrough of the ASSB technology is hindered by practical challenges in terms of processing, rate capability and cycle life. [2] Apart from high energy densities and a long cycle life, significantly enhanced safety properties are considered key for future battery technologies. Therein, the ASSB benefits from the absence of flammable liquid electrolyte as present in state-of-the-art LIBs. However, only very few studies were published showing the evaluation of the safety properties of lithium metal batteries. [3, 4] Therefore, this study aims on giving first insights into the factors influencing the thermal stability, hence the safety properties of different lithium metal battery (LMB) setups. As a baseline, lithium metal batteries based on liquid electrolyte were investigated in order to understand the influence of the lithium metal deposition behavior on the thermal stability of LMBs. Therein, during charging, lithium metal does not deposit homogeneously but forms dendritic or mossy structures often referred to as high surface area lithium (HSAL). [1, 5] At elevated temperatures, the high reactivity of HSAL can lead to fatal consequences, especailly in presence of liquid electrolyte (e.g. fire, explosion). Thus, the controlled deposition of lithium metal is crucial in order to guarantee safe operation of lithium metal batteries. This can be achieved by either modifying the charging process or the lithium metal surface (mechanically/chemically). Beyond that, lithium metal batteries based on either ceramic or polymer-based electrolytes are investigated. Therein, the cells are cycled to different sates of charge (SOC) and/or states of health (SOH) before analyzing the thermal stability by differential scanning calorimetry (DSC). This way, it is possible to determine distinct differences in the onset temperature for exothermic reactions and the evolving heat as a measure for the intensity of the reactions that might lead to a thermal runaway in large-scale cells. Moreover, the thermal stability of the cell components are characterized individually and in presence of each other du deduce interdependencies considering the chemical and thermal stability. In combination with comprehensive post-mortem analysis, it is possible to determine the factors influencing the thermal stability most. In summary, this study presents first results on the thermal stability of various LMB types to unravel the advantages/disadvantages compared to LIBs. [1] T. Placke, et al., J Solid State Electrochem 2017, 21, 1939-1964. [2] K. Kerman, et al., J Electrochem Soc 2017, 164, A1731-A1744. [3] T. Inoue, et al., ACS Appl Mater Interfaces 2017, 9, 1507-1515. [4] Uyama, et al., ACS Appl Energy Mater 2018, 1, 5712-5717. [5] M. Winter, et al., Adv Mater 1998, 10, 725-763.

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).

Recently, the demand for the middle- or large-sized lithium batteries with safety has increased. To solve this problem, all-solid state batteries (ASSBs) are actively researched. However, it is known that the ASSBs has a higher interfacial resistance than the conventional lithium batteries. Also, the ASSBs are operated at a high temperature of 60 to 80 °C, resulting in the degradation of the cycle performance due to the collapse of the structure of the active material. In this study, NCM materials were coated with TiO2 via sol-gel process. The crystal structure and surface morphology were observed according to TiO2 content and calcination temperature using X-ray diffraction (XRD), Scanning electron microscope (SEM), and Transmission electron microscope (TEM). Moreover, ASSBs were fabricated by using the TiO2-coated NCM as cathode, composite electrolyte (CE) and lithium metal as anode. Electrochemical characteristics were evaluated on the all-solid cells at 70°C, 0.1C. As a result, it has been found that the lattice parameters and crystal size of the NCM bulk are affected by the sintering temperature and the TiO2 coating content, which also affects the discharge capacity and cycle characteristics of the cells. We describe about the electrochemical behavior of NCM coatings by TiO2 in ASSBs in more detail.

All-solid-state batteries (ASSBs) are expected to have less safety concern than Lithium-ion batteries with organic liquid electrolyte (LIBs) because flammable liquid electrolytes are not used in ASSBs. The thermal behaviors in LIBs have widely discussed in many literatures1. However, thermal behaviors of ASSBs have not investigated much.In this study, to clarify the self-heating phenomenon of our prototype ASSB with Argyrodite-type solid electrolyte we have performed calorimetric studies and gas analyses. In the calorimetric measurement, an accelerated rate calorimetry (ARC) was used to compare the starting temperature of self-heating in ASSB to that in LIB. It was found that the self-heating of ASSB takes place at 200-300ºC which was significantly higher than that in LIB.To identify the endothermic and exothermic peaks in the calorimetric profile and to estimate the amount of heat generation in ASSB, a Calvet-type calorimeter (C600) and a differential scanning calorimeter (DSC) were used with a heating rate of 1 ℃/min under Ar atmosphere for a full cell and electrode layers of the ASSB, respectively. The exothermic peaks at 200- 300℃ for charged ASSB (at ca. 4.1 V) mostly corresponded to those for the cathode layer which was extracted from the charged ASSB. The crystal structure change of the cathode layer charged at ca. 4.1 V associated with temperature change was analyzed by X-ray diffraction (XRD) to understand the reaction mechanism. The XRD peaks for the active material and the solid electrolyte in the cathode layer were disappeared at 200-300ºC. It was suggested that the heat generation at 200- 300ºC were mainly caused by the reaction between the cathode active material and the solid electrolyte.We also analyzed the evolved gas during the heating of ASSB using a temperature-programmed desorption-mass spectrometry (TPD-MS). The detailed mechanism will be discussed on-site.AcknowledgmentsThis study was carried out in SOLiD-EV project supported by NEDO (New Energy and Industrial Technology Development Organization).References Xuning Feng, Minggao Ouyang, Xiang Liu, Languang Lu, Yong Xi, Xiangming He, Energy Storage Materials 10 (2018) 246-267.

All solid-state batteries (ASSBs) have the potential to deliver higher energy densities, wider operating temperature range and improved safety compared with today’s liquid electrolyte-based batteries. However, they still face challenges that limit their commercialization resulting from thick solid-state electrolytes (SSEs), and poor processability due to their unstable chemistries. Existing studies on solvent-binder based casting methods to reduce SSE thickness and improve processability still lack crucial fundamental understanding of the behavior and selection criteria for different SSE-binder-solvent systems. In this work, we attempt to isolate various SSE-binder-solvent system behaviors and study their chemical and electrochemical compatibilities using both bulk and surface sensitive characterization tools. With these findings, we introduce a novel binder-solvent combination that significantly reduces SSE thickness (~50 µm) and improves processability of ASSBs while maintaining high ionic conductivity (0.7 mS cm-1). The resulting organic/inorganic composite SSE was found to be stable against lithium metal by plating and stripping over 2000 hours at 0.11 mA cm-2 and 1.1 mAh cm-2. This study suggests the importance of understanding fundamental SSE-binder-solvent interactions and provides a potential design strategy for scalable production of ASSBs.

Size-controlled wet-chemical synthesis of sulfide superionic conductors for high-performance all-solid-state batteries

The thermal behavior is pivotal to the performance and safety of battery cells. To date, several thermal modeling approaches for lithium-ion batteries with liquid electrolyte (LiB) exist for different cell formats, tab designs, and more [1,2]. However, for all-solid-state batteries (ASSBs), relatively few publications exist on this topic.This presentation deals with sulfide-based ASSB cells. Although lab-sized ASSB cells perform well, cycling conditions in the lab still differ from practical applications. On the one hand, high pressure of several tens of MPa is usually applied during cycling to achieve good electrochemical behavior. On the other hand, separator thicknesses are in the range of several hundred µm due to difficulties in production and processability [3]. This results in low energy densities and prevents real-world application [4].Therefore, a direct comparison between lab-sized ASSB cells and existing LiB cells used in applications is neither reasonable nor possible. Today, it is still impossible to conclude whether ASSBs are truly superior to LiBs. To enable such a comparison, simulation techniques must be applied. Simulation-based upscaling of lab-sized ASSB cells to practical applications allows a fair comparison with LiBs.In this work, the thermal behavior of ASSB cells was investigated as a first step. A novel cell holder for calorimetric measurements of a lab-sized ASSB cell was developed. This cell holder allows for measurement of the heat generation of an ASSB cell in a commercial calorimeter (TAM IV, TA Instruments) while applying pressures of up to 30 MPa. By determining the thermal inertia of the cell holder and using a deconvolution algorithm [5], the original heat signal of the cell can be restored.After introducing the novel cell holder, measurement results of an ASSB cell (LiIn|LPSCl|LPSCl-NMC, 3.0 mAh) will be presented. This includes pressure-dependent results for 0.2 MPa, 10 MPa, 20 MPa, and 30 MPa, C-rates of 0.1C, 1C, and 4C, and temperatures of 25°C, 60°C, and 80°C. These data are crucial to determine the pressure-dependent interfacial resistances as well as the temperature-dependent ionic conductivity and electrochemical behavior of the cell. Furthermore, changes in stack pressure are tracked by a load cell. These results can later be used for mechanical simulations.The cell holder’s measurement results serve as input parameters for the thermal simulation. Different upscaled cell formats are investigated using parameters from the lab-sized cell. Thermal gradients and hotspots within the upscaled cells are identified and compared to LiBs. However, as the cell parameters are still unrealistic for practical applications - with a LiIn anode and a separator thickness of approximately 400 µm - these parameters are altered, starting from the validated lab-sized pouch cell. The thick separator dominates the averaged thermal parameters: heat capacity, thermal conductivity, and density of the cell. Assuming a thin separator of 20 µm leads to a 110% and 50% increase in thermal conductivity and density, respectively, but to a decrease in heat capacity of about 7%. This results in more heating of the cell but fewer thermal gradients.Furthermore, an electrochemical p2D model is parametrized and validated using the measured cycling data and the heat generation curve. Starting from the validated model, application-relevant separator thicknesses and a Li-metal anode are assumed. Lower overpotentials induced by the thinner separator lead to reduced heat generation. However, due to the reduced heat capacity, more cooling power is needed to minimize the heating of the cell.The p2D model is coupled with a thermal 3D model for different sizes and cell formats. Cooling strategies such as convective and tab cooling are compared in terms of effectiveness and electrochemical cell performance. Furthermore, the pressure-dependent measurement data are used to scale the performance for realistic pressure scenarios. Finally, an outlook is given on the thermal safety and runaway behavior of ASSBs.The simulation results enable a fair and realistic comparison of today’s LiBs with future sulfide-based ASSB technologies. Electrochemical behavior, the effort required for cooling strategies, and the resulting overall energy densities serve as indicators for the current progress in ASSBs and the further research necessary to transition ASSBs from laboratory research to real-world applications. Acknowledgment: This work was financially supported by the German Federal Ministry of Education and Research (BMBF) under grant number 03XP0597B (FB2-SAFE). The project is overseen by Project Management Juelich (PTJ).

Garnet-type solid-state electrolytes (SSEs) show a promising application in solid-state Li batteries. Poor interfacial contact with lithium causing large interfacial impedance and dendrite penetration is a problem. Inspired by unique H+/Li+ exchange of garnet electrolyte, we used an AgNO3 aqueous solution induced strategy to construct a lithiophilic layer in situ on the garnet surface without any specific apparatus. Experimental analysis reveals the uniform distribution of Ag nanoparticles and significantly enhanced affinity between the solid state electrolyte (SSE) and Li anode for the Li-Ag alloying. As expected, the interfacial area specific resistance (ASR) is greatly reduced to ∼4.5 Ω cm2, accompanying with long-cycling stability for ∼3500 h at 0.2 mA cm-2 and high critical current density of 0.75 mA cm-2. With modified SSEs, quasi-solid-state batteries with a LiFePO4 or LiNi0.5Co0.2Mn0.3O2 cathode operate well at room temperature and an all-solid-state LiFePO4/garnet/Li battery displays good cycling stability for over 200 cycles at 60 °C.

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.

Pivoting toward high-safety solid-state batteries, garnet-type solid-state electrolytes (SEs) with 3D ion transport channels are highly promising candidates. Complex cation substitutions are proved efficacious in enhancing ionic conductivity, while the role of pre-exponential factor in Arrhenius equation receives insufficient attention compared to the activation energy term. Herein, multiple lattice site substitution is employed to elucidate the contribution of increased configurational entropy to phase formation and the predominance of local distortion on ionic conductivity. Neutron diffraction and density functional theory calculations reveal the highly-distorted Li coordination environments leading to a decrease of activation energy. However, this effect is simultaneously compensated by decreased migration entropy and hopping frequency, hampering the enhancement of ionic conductivity. In the study, Li6.3Ga0.1La3Zr0.8Hf0.8Ta0.2Nb0.2O12 with rational-designed local distortion shows the optimized ionic conductivity due to the trade-off between activation energy and pre-exponential factor. This work demonstrates an approach of high-entropy strategy to advancing the ionic transport behavior of SEs.