Wet-chemical synthesis of Li7P3S11 with tailored particle size for solid state electrolytes

This research investigated new materials and improvements to the performance of solid state batteries in order to achieve high performance, but with acute attention to safety and manufacturability. It is widely known that liquid-based lithium-ion batteries maintain inherent safety problems on account of solvent leakage and flammability of liquid electrolytes used in commercial lithium-ion batteries.1,2 Additionally, liquid-electrolyte-containing lithium-ion batteries must be constructed in such a way to account for their inherent danger, requiring excess weight in safety containment materials, which diminishes their overall energy density and adds to manufacturing costs. In contrast to commercialized liquid-electrolyte-based lithium-ion batteries, all-solid-state batteries offer ultimate safety and potential for high energy/power density due to increased packing efficiency in final battery designs with the elimination of unnecessary safety equipment.3,4 Unfortunately current research and development efforts have yet to unveil an all-solid-state battery that can fulfill all metrics for world-wide replacement of liquid-electrolyte based lithium-ion batteries. The key issue blocking commercial-scale deployment of all-solid-state batteries is not a lack of capable bulk materials to construct the batteries; but the interfacial reactions that happen between materials within the battery in contact with one-another that prevent maintained high performance. All-solid-state secondary batteries employing inorganic solid state electrolytes (SEs) offer a significant, inherent safety advantage over conventional liquid-electrolyte-containing batteries making them highly desirable for next generation energy storage. Key to the ultimate safety of all-solid-state secondary batteries is the SE which functions electrochemically and structurally within the battery. Much effort has gone into developing new SEs with excellent electrochemical characteristics such as high ionic conductivity and high voltage chemical stability, as well as into its structural role as the battery separator. Until recently, commercialization of all-solid-state secondary batteries has not been possible due to low conductivity of the SE as compared to batteries with liquid electrolyte. However, numerous groups have demonstrated SEs with high ionic conductivity on the order of 10-4-10-2 S cm-1 which engenders the opportunity for parallel performance between all-solid-state batteries and conventional batteries. As a final hurdle to realistically enable all-solid-state batteries as a viable, commercializable energy source it is critical to resolve the chemical instability between the SE and bulk electrode materials contained within batteries. It is now widely accepted that the interfaces of lithium-ion battery (LIB) electrode materials can be highly dynamic in nature, and are the source of performance fade problems as well as safety issues. Atomic Layer Deposition (ALD) has been widely demonstrated as an elegant technique for addressing the shortcomings of battery performance, and has recently being demonstrated as a means for enhancing safety. Here, we will discuss recent advances in ALD coatings applied to battery materials which significantly increase the performance as well as safe handling, production, and use of a final batteries.

Electrochemical Energy Storage with Mediator-Ion Solid Electrolytes

Stabilizing Solid Electrolyte-Anode Interface in Li-Metal Batteries by Boron Nitride-Based Nanocomposite Coating

Commercial lithium-ion batteries have inherent safety problems due to the usage of non-aqueous electrolyte as the electrolytes. The development of solid state lithium metal batteries is expected to solve these problems while achieving higher energy density. However, the problem of lithium plating still exists. This article reviews the deposition behavior of lithium metal anodes in solid-state batteries, and provides suggestions for high-energy-density and high-safety solid-state lithium batteries. This paper systematically summarizes the mechanism of Li deposition in polymers and inorganic solid state electrolytes, and discusses the strategies of controlling lithium deposition and preventing lithium dendrites and the characterization of Li metal anodes. In solid-state batteries, poor solid-solid contact between the electrolyte and the anode, defects, grain boundaries, cracks, pores, enhanced electric and ionic fields near the tip, and high electronic conductivity of the solid state electrolyte can all lead to lithium deposition, which may evolve into lithium dendrites. There are several strategies to control lithium deposition: 1). Use functional materials and structure design to induce uniform deposition of lithium, such as improving the solid state electrolyte/anode interfacial contact, using lithiophilic coatings or sites, and designing three-dimensional structure electrodes and solid state electrolytes. 2). Suppress the generation of lithium dendrites, such as limiting the free movement of anions in solid state electrolytes (especially polymer solid electrolytes), to reduce local space charge which induces lithium dendrites. In addition, optimizing the solid electrolyte synthesis process to reduce lithium dendrites caused by defects is also an important method. 3). Strategies for dendrites already formed are essential for safety concern. The dendritic deposition is one of the intrinsic properties of lithium. Thus, there is no guarantee that there will be no lithium dendrites, especially at high current density. Once lithium dendrites are formed, countermeasures are required. For example, improving the mechanical strength of solid state electrolytes, and using self-healing materials, structures, and cycling conditions are proposed to avoid safety hazards caused by lithium dendrites piercing. This article focuses on the control of lithium deposition. Suppressing lithium dendrites only solves a little problem of the application of lithium metal anodes. In the future, in order to use lithium metal as a negative electrode in practical all-solid-state batteries, many challenges need to be overcome, such as irreversible side reactions between lithium and other materials, safety and volume change of composite lithium anodes. In addition, in order to allow the laboratory's research results to be quickly transformed into applications, it is also necessary to establish battery design, assembly, and test standards that are in agreement with practical requirements. In short, all-solid-state lithium batteries still have a long way to go, but they have great potential for safe, high-performance, and low-cost energy storage systems in the future.

Toward an Atomistic Understanding of Solid-State Electrochemical Interfaces for Energy Storage

The realization of all-solid-state lithium-ion batteries (LIBs) is often considered as the final challenge in the development of LIBs. Replacing Li-ion conductive liquid electrolytes with high-performance solid-state electrolytes is indispensable for the development of all-solid-state LIBs. Solid-state electrolytes under development fall into three classes: polymers, oxides, and sulfides. Polymer-based electrolytes have advantages over oxides and sulfides, such as formation of low-resistance electrolyte/electrode interfaces, good processability, and high energy-density owing to low density. Therefore, polymer-based solid-state electrolytes are being developed in both industry and academia as a practical route for realizing high-capacity LIBs.[1]For application in commercial LIBs, the electrolyte should have an ionic conductivity higher than 10-4 S/cm at room temperature. Conventional solid polymer electrolytes, such as polyethylene oxide (PEO)-based electrolytes, do not meet the performance requirements due to insufficient ionic conductivity in the range of 10-6 to 10-5 S/cm. Recently, polyphenylene sulfide (PPS)-based polymer electrolytes have been reported to yield ion conductivities as high as those of liquid electrolytes over a wide temperature range (> 1.0 × 10-4 S/cm at 25 °C, > 1.0 × 10-3 S/cm at 80 °C, and > 1.0 × 10-3 S/cm at −40 °C).[2] These electrolytes consist of base polymer chains containing PPS, Li salts that can dissociate into cations and anions, and neutral agent molecules. However, the detailed Li-ion transport mechanism in terms of the respective roles of the molecular components of PPS electrolytes is yet to be determined. This limited understanding hinders the further improvement of PPS-based electrolytes.In this study, we perform a series of first-principle calculations and demonstrate that certain types of neutral molecules (so-called agent molecules) accelerate solid-state lithium-ion migration when mixed with lithium salts.[3] We find that the intermolecular interaction in a selected agent-molecule/lithium-salt binary system is governed by the strong coupling between lithium and oxygen atoms. Upon the addition of agent molecules, the anionic species surrounding the lithium of lithium salts is replaced by the agent molecules. The resulting weakened Coulomb energy coupling between lithium and oxygen atoms is determined to be a key factor in enabling fast lithium-ion migration via facile dissociation of lithium salts and subsequent formation of ion-hopping sites in the form of lithium-free oxygen-cages. The structure-based interpretation of agent molecules suggests that neutral molecules with functional groups which enhance chemical resonance can be selected as potential agent molecules. We believe that the results obtained in this study serve as a theoretical basis for the future development of solid-state polymer electrolytes, particularly toward mitigating the dependence of lithium-ion transport on the movement of polymer chains.

Pseudo-solid State Batteries See the Light

The development of solid-state lithium-ion batteries (LIBs) is a key advancement in energy storage technology. Solid electrolytes are important in this development because they are safer and more stable than liquid electrolytes, and they have higher energy density. Among the various types of solid electrolytes, Polyphenylene Sulfide (PPS)-based solid-state polymer electrolytes (SPEs) are notable for their ability to conduct ions as well as liquid electrolytes across a wide range of temperatures. This ability is particularly important because other solid polymer electrolytes, like those based on polyethylene oxide (PEO), struggle with ion conduction at different temperatures. PPS-based SPEs are different because their ion transport does not depend on the movement of the polymer chains, which means their ion conduction remains steady from high to low temperatures.The previous study conducted a series of first-principle calculations, revealing that the introduction of neutral molecules, referred to as agent molecules, can significantly enhance the movement of lithium ions within a solid matrix when these are mixed with lithium salts. This is because the intermolecular interactions within a binary system comprising an agent molecule and lithium salt are governed by a strong bond formation between lithium and oxygen atoms. When these agent molecules are introduced, they replace the anionic species around lithium in the salts, leading to a weakened Coulomb force between lithium and oxygen. This reduction is essential for rapid lithium-ion movement through the easy separation of lithium salts and the subsequent generation of ion-hopping sites characterized as lithium-free oxygen cages. According to the previous study, the strategic selection of neutral molecules with functional groups that bolster chemical resonance is imperative. Such molecules have been identified as promising candidates for agent molecules.Our study builds upon previous research by directly incorporating PPS polymers into our computational simulations. We utilized molecular dynamics and quantum mechanics to examine the role of neutral molecules in PPS in facilitating lithium-ion mobility. We parameterized our system with quantum mechanics calculations, which were crucial in informing our molecular dynamics simulations. Using VASP program for interaction assessment and LAMMPS program for energy and structure analysis, we refined our models to understand the interactions between PPS polymers, Li+ ions, TFSI- ions, and Chloranil molecules. Our simulations explored the structural dynamics and the effects of fillers and PPS polymer layers on ion transport.Our work enhances the basic understanding of SPEs and helps in the creation of new lithium-ion batteries that perform better and are safer. We've pinpointed important factors that control how lithium ions move in PPS-based electrolytes, laying the groundwork for future improvements in solid-state electrolytes and leading to lithium-ion batteries that are more effective and safer.Reference:[1] Jiwon Yu, Myungsuk Lee, Yeonseo Kim, Hyung-Kyu Lim, Jonghyun Chae, Gyeong S. Hwang, Sangheon Lee, “Agent molecule modulated low-temperature activation of solid-state lithium-ion transport for polymer electrolytes”, Journal of Power Sources 505, 229917 (2021).

An overview of ion transport in lithium-ion inorganic solid state electrolytes is presented, aimed at exploring and designing better electrolyte materials. Ionic conductivity is one of the most important indices of the performance of inorganic solid state electrolytes. The general definition of solid state electrolytes is presented in terms of their role in a working cell (to convey ions while isolate electrons), and the history of solid electrolyte development is briefly summarized. Ways of using the available theoretical models and experimental methods to characterize lithium-ion transport in solid state electrolytes are systematically introduced. Then the various factors that affect ionic conductivity are itemized, including mainly structural disorder, composite materials and interface effects between a solid electrolyte and an electrode. Finally, strategies for future material systems, for synthesis and characterization methods, and for theory and calculation are proposed, aiming to help accelerate the design and development of new solid electrolytes.

Rechargeable lithium ion batteries become an very important technology in the contemporary society. They are expanding their application in electric vehicles and power grids. However, current lithium ion batteries with liquid electrolyte have been suffering from potential safety crisis mainly due to their highly flammable organic liquid carbonate organic electrolyte and explosion hazards. These potential risks (combustion and explosion) would retard the commercialization of electric vehicles or hybrid electric vehicles. Thus, the safety issue of lithium ion battery merits further study. Solid electrolytes have attracted ever-increasing interest owing to their enhanced safety issue and higher energy density of lithium battery. Solid electrolyte materials mainly include inorganic solid electrolytes (ISEs) and solid polymer electrolytes (SPEs). The ISEs are classified into oxide-based, sulfide-based and etc. However, in spite of the presence of highly ion conductive ISEs, there are still many undergoing issues that limit the practical application at the present stage, like the large interface impedance between electrode and ISEs and the difficulty of processing. More attention has been paid to solid polymer electrolytes due to their superior flexibility and processability, which are also subjected to thermal expansion at elevated temperature. Poly(ethylene oxide) (PEO) solid polymer electrolyte has undergone a sort of renaissance in the past few decades. However, the quintessential frailty of PEO solid polymer electrolyte is low ionic conductivity (in the order of 10(-7) S cm(-1)) at room temperature with a relatively narrow electrochemical window. Hence, it is essential to develop new solid polymer electrolytes with comprehensive performance in terms of high ionic conductivity, wide electrochemical window, superior mechanical strength, excellent thermal stability as well as good interfacial compatibility. In this review, a series of polycarbonate-based solid polymer electrolytes (such as PEC, PPC, PTMC and PVC et al.) are summarized. In addition, we also present a brief review on preparation, electrochemical property, modification, ionic transportation mechanism and future development direction for each of these solid polymer electrolytes.

Recent progress, challenges, and perspectives in the development of solid-state electrolytes for sodium batteries

Review: 162 refs.

Lithium metal anodes hold the promise to significantly increase the energy density of current Li-ion batteries by replacing the bulkier graphite anode. However, these batteries have low cycling efficiency and internal short circuiting due to metal dendrites. A strategy to prevent dendritic growth is using a stiff solid electrolyte that can mechanically block their growth, while in reality, penetration through the tough solid electrolytes by soft Li metal filaments still occurs at a relatively low critical current density.Inspired by the dendrite initiation at the system-specific limiting current in liquid electrolytes, we explore the possibility in this study that dendrite growth in solid state electrolytes at the critical current density (CCD) is a transport limited phenomenon determined by ionic conduction. Previous studies have used galvanostatic cycling [1] as the basis for measuring the CCD, however cycling presents problems of interfacial stripping and delamination leading to a reduction in contact surface area and high localized current densities. Here we use linear sweep voltammetry (LSV) with the implementation of stack pressure to mitigate these effects to initially determine the CCD and develop a model connected to the ionic conduction. With the experimentally determined CCD, we then investigate the penetration time at various higher-than-CCD constant current densities to uncover a Sand’s time-like behavior, which offers insights on the transport dynamics consistent with our previous work [2]. Operando and postmortem analyses were also performed to complement the electrochemical characterization toward a self-consistent comprehensive understanding. In conclusion, our new method allows us to understand the growth mechanism of dendrites in solid electrolytes, while still connecting microstructural and interfacial aspects from previous published works[3][4], to present a unified approach to understanding the metal dendrite initiation at the CCD.References E. Kazyak, R. Garcia-Mendez, W.S. LePage, A. Sharafi, A.L. Davis, A.J. Sanchez, K.-H. Chen, C. Haslam, J. Sakamoto and N.P. Dasgupta. Li Penetration in Ceramic Solid Electrolytes: Operando Microscopy Analysis of Morphology, Propagation, and Reversibility. Matter 2, 1025-1048, (2020).P. Bai, J. Li, F.R. Brushett and M.Z. Bazant. Transition of lithium growth mechanisms in liquid electrolytes. Energ Environ Sci 9, 3221-3229, (2016).L. Porz, T. Swamy, B.W. Sheldon, D. Rettenwander, T. Frömling, H.L. Thaman, S. Berendts, R. Uecker, W.C. Carter and Y.-M. Chiang. Mechanism of Lithium Metal Penetration through Inorganic Solid Electrolytes. Advanced Energy Materials 7, 1701003-n/a, (2017).T. Krauskopf, H. Hartmann, W.G. Zeier and J. Janek. Toward a Fundamental Understanding of the Lithium Metal Anode in Solid-State Batteries—An Electrochemo-Mechanical Study on the Garnet-Type Solid Electrolyte Li6.25Al0.25La3Zr2O12. ACS Applied Materials & Interfaces 11, 14463-14477, (2019). Figure 1

Lithium-ion batteries are the energy storage devices of choice not only for portable devices but electric vehicles and grid energy storage as well due to their high gravimetric and volumetric energy density. Their ancestors, the lithium metal batteries offer way higher capacities but suffered severely from safety issues due to the dendrite formation. Solid state electrolytes; e.g. LISICON, garnets, perovskites, etc.; may mitigate this risk but suffer from low ionic conductivity (<10-4 S/cm). [1] The interfacial resistance between the electrode and the solid electrolyte is also very challenging. Hybrid solid state electrolytes can address these issues and allow for an easier implementation into conventional battery technology. The hybrid solid state electrolyte combines the desirable properties of both liquid and solid electrolytes by confining liquid electrolytes within a (meso-)porous solid framework.[2,3] This approach allows to maintain the high ionic conductivity and intimate contact with the electrodes while offering the safety of solid electrolytes. Our group developed the eutectogels in which a deep eutectic electrolyte (binary mixture of N-methylacetamide and LiTFSI) is confined within a porous silica framework designed via a facile one-pot non-aqeous sol-gel route.[4] This hybrid electrolyte can act as a greener and cheaper alternative to the well-known ionogels.[5] The eutectogels offer a broad electrochemical window, with a beneficial anodic stability limit of up to 4.8 V vs Li+/Li while impedance spectroscopy revealed ionic conductivities of up to 1.46 mS/cm at room temperature for the optimal composition. LiFePO4 (LFP) demonstrator half-cells were assembled with these hybrid solid state electrolyte membranes and displayed a highly reversible capacity for over 100 cycles. Elaborate electrochemical characterization reveals the promising nature of this newest member of the hybrid solid electrolyte family. In the current presentation, we will show the expansion of the eutectogel family via two pathways. First, new deep eutectic electrolytes with higher thermal stability have been designed and confined within a silica matrix. The compositions have been optimized and fully (electro-)chemically characterized for their potential in electrochemical cells. Another route is replacing the silica framework with a polymeric cage. This route allows the further simplification of the synthesis while fully harnessing the potential of the confined deep eutectic electrolyte. Both routes are evaluated for their potential to formulate the design principles for the development of novel eutectogels. Figures Figure 1: (Left) Synthesis route for the eutectogels, optical photograph of a membrane (12 mm diameter) with schematic representation of the nanostructure. (Right) Arrhenius plots of the ionic conductivities for several compositions. Acknowledgements B. Joos is a PhD fellow of the Research Foundation – Flanders (FWO Vlaanderen). This project receives the support of the European Union, the European Regional Development Fund ERDF, Flanders Innovation & Entrepreneurship and the Province of Limburg (project number EFRO936). The authors would like to thank other group members for their assistance.

<p indent="0mm">In recent years, with the rapid developments of high-technology industries such as information technology and electric vehicles, there are urgent need to develop new generations of lithium-ion batteries with higher energy density, longer cycle life and improved safety. In addition to the development of high specific energy cathode and high specific capacity anode materials, regulating the stability of the electrode/electrolyte interface is critical to achieve and balance various performances of the batteries and finally realize their commercial application widely. However, the traditional carbonate electrolytes not only suffer from severe oxidation decomposition when the charging voltage is higher than 4.3 V (vs. Li/Li⁺), but also show poor compatibility with high-capacity silicon or silicon-carbon (Si-C) composite anodes and lithium metal anodes. Moreover, the traditional carbonate electrolytes are flammable, which is still a big safety concern to address for lithium ion battery. Therefore, rational design of electrolytes that match the high voltage cathode, high specific capacity Si-C abode or lithium metal anode, and has better safety property and especially under harsh conditions, has become a decisive factor for the rapid developments of high specific energy lithium-ion batteries. The present work reviews different kinds of liquid electrolytes with functional additives and utilization of solid state electrolytes which are explored by our group in the past 15 years. The design strategies and systematic investigations of the electrolytes recipes include: (1) Developing anti-oxidation solvent systems, for example, applications of new high-voltage nitriles or fluorinated solvents for high-voltage cathodes, such as suberonitrile (SUN), fluoroethylene carbonate (FEC) and ethyl-(2,2,2-trifluoroethyl) carbonate (ETFEC); (2) exploiting some novel multifunctional solvents or additives which contain flame retardant groups or can be used as film-forming agents for high-voltage cathodes. For example, some P-containing compounds such as <italic>N</italic>,<italic>N</italic>-diallyl-diethoxy phosphoramide (DADEPA), phenoxy cyclophosphazene (PFPN), and ionic liquid such as N-methyl-N-butylpyrrolidinium bis(trifluoromethylsulfonyl)imide (Py14TFSI), etc. In addition, we have also investigated a series of solid electrolytes such as Garnet-type electrolytes, gel polymer or composite polymer electrolyte with inorganic additives, which could greatly reduce the safety risk of batteries. These works include measurements of the activation energy and ion transport mechanism of oxide solid electrolyte with solid NMR techniques, interface modification of sulfide-type solid state battery with ionic liquids, and interface passivation mechanism of PEO-based polymer electrolyte, etc. Finally, some discussions and future perspectives in developing high-voltage and highly-safe liquid electrolyte and flexible solid-state electrolytes for all solid state batteries are presented. Although the commonly used high-voltage electrolytes are mainly composed of lithium salts, anti-oxidation solvents and functional additives such as nitriles, sulfones, fluoro-ethers or fluoro-carbonates, However, the acting mechanisms of those high-voltage electrolytes, especially solvents, salts and additives, are still not clear, especially the composition, structure and evolution of the electrochemical interfaces are lack of quantitative understanding. Therefore, combining theoretical calculation and advanced in-/ex-situ interface characterization techniques, fully understanding the working mechanism of the additives in high-voltage systems and the effective components of interface film, and designing novel functional electrolyte additives are crucial for the development of a new generation of high-specific energy lithium batteries. In addition, applications of flame-retardant solvents or additives to develop flame-retardant liquid-type electrolytes and developing new solid state electrolytes are both important strategies to reduce the potential safety hazards of lithium ion batteries. The future research should focus on how to improve the compatibility between flame-retardant solvents/additives and the cathode/anode interfaces in liquid electrolytes, minimize the negative impact on battery performance (cycle performance, rate performance, etc.), enhance the ionic conductivity and mechanical flexibilities of the solid electrolytes, optimize the electrolyte phase structure/mechanical properties, and regulate the stability of interfaces to ensure the long-term cycling stability of lithium metal anodes and metal oxide cathodes.