Development Of Solid-state Electrolytes Research Articles

Molten Guest-Mediated Metal-Organic Frameworks Featuring Multi-Modal Supramolecular Interaction Sites for Flame-Retardant Superionic Conductor in All-Solid-State Batteries.

The development of solid-state electrolytes (SSEs) with outstanding comprehensive performance is currently a critical challenge for achieving high energy density and safer solid-state batteries (SSBs). In this study, a strategy of nano-confined in situ solidification is proposed to create a novel category of molten guest-mediated metal-organic frameworks, named MGM-MOFs. By embedding the newly developed molten crystalline organic electrolyte (ML20) into the nanocages of anionic MOF-OH, MGM-MOF-OH, characterized by multi-modal supramolecular interaction sites and continuous negative electrostatic environments within nano-channels, is achieved. These nanochannels promote ion transport through the successive hopping of Li+ between neighbored negative electrostatic environments and suppress anion movement through the chemical constraint of the hydroxyl-functionalized pore wall. This results in remarkable Li+ conductivity of 7.1 × 10-4 S cm-1 and high Li+ transference number of 0.81. Leveraging these advantages, the SSBs assembled with MGM-MOF-OH exhibit impressive cycle stability and a high specific energy density of 410.5Wh kganode + cathode + electrolyte -1 under constrained conditions and various working temperatures. Unlike flammable traditional MOFs, MGM-MOF-OH demonstrates high robustness under various harsh conditions, including ignition, high voltage, and extended to humidity.

Fluorinated Graphene Fillers for High-Performance Solid-State Lithium Batteries

Solid-state batteries (SSBs) are expected to revolutionize the field of energy storage due to their superior safety and high energy density, which result from the use of lithium metal as the negative electrode. However, the development of solid-state electrolytes (SSEs), the key component of SSBs, is quite crucial. SSEs have high thermal stability, high mechanical strength, and a wide electrochemical window but lack enough ionic conductivity; which is one of the most challenging aspects. Incorporating suitable active or inert fillers in the solid polymer electrolyte matrix is one of several methods adopted to improve the ionic conductivity of pure polymer SSEs. Two-dimensional graphene-based fillers are a promising option as they provide a high surface area for creating an abundant interface with the polymer matrix creating a continuous pathway for lithium-ion transport and simultaneously their robust nature improves the mechanical strength of the electrolyte. Pristine graphene is electronically conducting in nature owing to the continuous sp2 carbon linkages, but the electronic conductivity can be suppressed by disrupting the sp2 bonds by heteroatom functionalization on the graphene. This study investigates the heteroatom functionalization of graphene to obtain various graphene-based fillers such as graphene oxide (GO), reduced graphene oxide (rGO), and fluorinated graphene oxide (FGO) and their effectiveness when introduced into a polymer SSE matrix for LiNi0.8Co0.1Mn0.1O2-based SSBs. FGO filler outperforms others in terms of ionic conductivity, thermal stability, enhanced electrochemical potential window, and compatibility of the SSE. The optimized ratio of FGO fillers in SSE demonstrates excellent electrochemical performance, enabling long-term Li plating/stripping with small overpotential and stable cycling of Li/ LiNi0.8Co0.1Mn0.1O2 full cells. This work highlights the notable potential of FGO materials in improving the comprehensive properties of polymer SSEs and promoting the applications of polymer SSEs in high-performance SSBs.

Dual Interface Compatibility Enabled via Composite Solid Electrolyte with High Transference Number for Long-Life All-Solid-State Lithium Metal Batteries.

The development of solid-state electrolytes (SSEs) effectively solves the safety problem derived from dendrite growth and volume change of lithium during cycling. In the meantime, the SSEs possess non-flammability compared to conventional organic liquid electrolytes. Replacing liquid electrolytes with SSEs to assemble all-solid-state lithium metal batteries (ASSLMBs) has garnered significant attention as a promising energy storage/conversion technology for the future. Herein, a composite solid electrolyte containing two inorganic components (Li6.25 Al0.25 La3 Zr2 O12 , Al2 O3 ) and an organic polyvinylidene difluoride matrix is designed rationally. X-ray photoelectron spectroscopy and density functional theory calculation results demonstrate the synergistic effect among the components, which results in enhanced ionic conductivity, high lithium-ion transference number, extended electrochemical window, and outstanding dual interface compatibility. As a result, Li||Li symmetric battery maintains a stable cycle for over 2500h. Moreover, all-solid-state lithium metal battery assembled with LiNi0.6 Co0.2 Mn0.2 O2 cathode delivers a high discharge capacity of 168mAhg-1 after 360 cycles at 0.1C at 25°C, and all-solid-state lithium-sulfur battery also exhibits a high initial discharge capacity of 912mAhg-1 at 0.1C. This work demonstrates a long-life flexible composite solid electrolyte with excellent interface compatibility, providing an innovative way for the rational construction of next-generation high-energy-density ASSLMBs.

A Minireview of the Solid-State Electrolytes for Zinc Batteries.

Aqueous zinc-ion batteries (ZIBs) have gained significant recognition as highly promising rechargeable batteries for the future due to their exceptional safety, low operating costs, and environmental advantages. Nevertheless, the widespread utilization of ZIBs for energy storage has been hindered by inherent challenges associated with aqueous electrolytes, including water decomposition reactions, evaporation, and liquid leakage. Fortunately, recent advances in solid-state electrolyte research have demonstrated great potential in resolving these challenges. Moreover, the flexibility and new chemistry of solid-state electrolytes offer further opportunities for their applications in wearable electronic devices and multifunctional settings. Nonetheless, despite the growing popularity of solid-state electrolyte-based-ZIBs in recent years, the development of solid-state electrolytes is still in its early stages. Bridging the substantial gap that exists is crucial before solid-state ZIBs become a practical reality. This review presents the advancements in various types of solid-state electrolytes for ZIBs, including film separators, inorganic additives, and organic polymers. Furthermore, it discusses the performance and impact of solid-state electrolytes. Finally, it outlines future directions for the development of solid-state ZIBs.

Correlated factors for Li-ion migration in ionic conductors with the fcc anion sublattice.

The development of solid-state electrolytes (SSEs) with high lithium ionic conductivities is critical for the realization of all-solid-state Li-ion batteries. Crystal structure distortions, Li polyhedron volumes, and anion charges in SSEs are reported to affect the energy landscapes, and it is paramount to investigate their correlations. Our works uncover the cooperative effect of lithium site distortions, anion charges, and lattice volumes on Li-ion migration energy barrier in superionic conductors of LiMS2 (M = Sc, Ti, V, Cr, Mn, Fe, Co, and Ni) and Li2MO3 (M = Sc, Ti, V, Cr, Mn, Fe, Co, and Ni). Combined with the Least Absolute Shrinkage and Selection Operator analyses, the volume and Continuous symmetrical methods (CSMs) of Li tetrahedral (Tet) sites appear to have a larger effect on the manipulation of Ea for Li migration, compared to that of Li octahedral (Oct) sites, which is further confirmed by the results from the face-centered cubic (fcc) anion lattice model. For the Tet-Oct-Tet Li migration path, the CSM (the volume of Li site) has a negative (positive) correlation with Ea, while for the Oct-Tet-Oct Li migration paths, opposite correlations have been observed. The understanding of the correlation between site preference, anion charge, lattice volume, and structural distortion as well as the prediction model of Ea in terms of these three factors, namely, C-V-D model, could be useful for the design of solid-state electrolytes with lower activation energy.

Effect of Charge Non-Uniformity on the Lithium Dendrites and Improvement by the LiF Interfacial Layer

All-solid-state lithium metal batteries with high safety and high energy density have received widespread attention. However, the development of solid-state electrolytes (SSEs) is limited by the growth of lithium dendrites. In this paper, by using density functional theory, we investigated the charge density distribution uniformity of the neutral systems and the system with excess electrons on the surface of cubic Li7La3Zr2O12 (c-LLZO). Our results show that the surface of c-LLZO can be easily occupied by excess electrons and its charge density distribution is uneven, which causes lithium ions to aggregate in areas with higher charge density and reduce to metallic lithium and eventually results in the lithium dendrite formation. We also found that the use of a LiF buffer layer can make the charge density distribution near the interface layer more uniform, thereby inhibiting the growth of lithium dendrites. Such theoretical results well explain the role of LiF in SSEs and offer a promising way to prevent the lithium dendrite formation.

Synthesis and Modification of Tetrahedron Li10.35Si1.35P1.65S12via Elemental Doping for All-Solid-State Lithium Batteries

Solid-state electrolyte (SSE), as the core component of solid-state batteries, plays a critical role in the performance of the batteries. Currently, the development of SSE is still hindered by its high price, low ionic conductivity, and poor interface stability. In this work, we report the tailored synthesis of a high ionic conductive and low cost sulfide SSE for all-solid-state lithium batteries. The Li10.35Si1.35P1.65S12 with favorable tetragonal structure was synthesis by increasing the concentration of Si4+, which shows an ionic conductivity of 4.28 × 10−3 S cm−1 and a wide electrochemical stability window of up to 5 V. By further modifying the composition of the electrolyte via ionic doping, the ionic conductivity of Li10.35Si1.35P1.65S12 can be further enhanced. Among them, the 1% Co4+-doped Li10.35Si1.35P1.65S12 shows the highest ionic conductivity of 6.91 × 10−3 S cm−1, 40% higher than the undoped one. This can be attributed to the broadened MS4 − tetrahedrons and increased Li+ concentration. As a demonstration, an all-solid-state Li metal battery was assembled using TiS2 as the cathode and 1% Co4+-doped Li10.35Si1.35P1.65S12 as the electrolyte, showing capacity retention of 72% at the 110th cycle. This strategy is simple and can be easily extended for the construction of other high-performance sulfide SSEs.

Double-Layer Solid Composite Electrolytes Enabling Improved Room-Temperature Cycling Performance for High-Voltage Lithium Metal Batteries.

The development of solid-state electrolytes (SSEs) for high energy density lithium metal batteries (LMBs) usually needs to take into account of the interfacial compatibility against lithium metal and the electrolyte stability suitable for a high-potential cathode. In this study, through a facile two-step coating process, novel double-layer solid composite electrolytes (SCEs) with Janus characteristics are customized for the high-voltage LMBs with improved room-temperature cycling performance. Among which, high-voltage resistant poly(vinylidene fluoride) (PVDF) is adopted here for the construction of an electrolyte layer facing the cathode, while the other layer against the lithium anode is composed of the polymer matrix of poly(ethylene oxide) (PEO) blended with PVDF to obtain a lithium metal-friendly interface. With the further incorporation of Laponite clay, the PVDF/(PEO+PVDF)-L SCEs not only exhibit improved mechanical properties, but also achieve a highly increased ionic conductivity (5.2 × 10–4 S cm–1) and lithium ion migration number (0.471) at room temperature. The assembled NCM523|PVDF/(PEO+PVDF)-L SCEs|Li cells thus are able to deliver the initial discharge capacity of 153.9 mAh g–1 with 80.8% capacity retention after 200 cycles at 0.3 C. Such easily manufactured double-layer SCEs capable of operating steadily at room temperature provide a competitive electrolyte option for high-voltage solid-state LMBs.

Li1.4Al0.4Ge0.4Ti1.4(PO4)3 promising NASICON-structured glass-ceramic electrolyte for all-solid-state Li-based batteries: Unravelling the effect of diboron trioxide

Li-ion batteries (LIBs) are the ubiquitous technology to power portable electronics; however, for the next-generation of high-performing electrochemical energy storage systems for electric vehicles and smart grid facilities, breakthroughs are needed, particularly in the development of solid-state electrolytes, which may allow for enhanced energy density while enabling lithium metal anodes, combined with unrivalled safety and operative reliability. In this respect, here we present the successful synthesis of a glass-ceramic Li1.4Al0.4Ge0.4Ti1.4(PO4)3 NASICON-type solid-state electrolyte (SSE) through a melt-casting technique. Being grain boundaries crucial for the total ionic conductivity of SSEs, the effect of the addition of diboron trioxide (B2O3, 0.05 wt.%) to promote their liquefaction and restructuring is investigated, along with the effects on the resulting microstructures and ionic conductivities. By the thorough combination of structural-morphological and electrochemical techniques, we demonstrate that bulk materials show improved performance compared to their powder sintered counterpart, achieving remarkable ion mobility (> 0.1 mS cm–1 at –10 °C) and anodic oxidation stability (> 4.8 V vs Li+/Li). The addition of B2O3 positively affects the grain cohesion and growth, thus reducing the extension of the grain boundaries (and the related grain/grain interface resistance) and, therefore, increasing the overall ion mobility. In addition, B2O3 is seen to contrast the microcracks formation in the LAGTP system under study which, overall, shows very promising prospects as SSE for the next-generation of high-energy density, safe lithium-based batteries.

Halide Solid-State Electrolytes: Synthesize and the Atmospheric Stability Study

Rechargeable all-solid-state Li batteries (ASSLBs) are considered as the next generation of electrochemical energy storage systems. Development of solid-state electrolytes (SSEs), which are key materials for ASSLBs, is therefore one of the most important subjects in modern energy storage chemistry. Thus, various types of electrolytes such as polymer-, oxide-, and sulfide-based SSEs have been developed to date and the development of new superionic conductors is still ongoing. Halide SSEs (Li-M-X, M is a metal element, and X is a halogen) are emerging as promising candidates with a number of attractive properties (oxidative stability and interfacial compatibility, etc.). [1] For example, halide SSEs show advantages including high ionic conductivity, wide electrochemical stability windows (0.36-6.71 V vs. Li/Li+), and improved chemical stability toward cathode materials compared to other SSEs. [2-4] Moreover, some of the halide SSEs (such as Li3InCl6 developed by our group) can be directly synthesized in a water solvent with the capability of large-scale production, thus removing the need for special apparatus or handling in an inert atmosphere.In this talk, (i) I will demonstrate the new and salable water-mediated synthesis method of the highly conductive Li3InCl6 halide SSE [5]. (ii) I will report the anion sublattice evolution effect on Li+ conductivity for halide SSEs [6]. I will also show the humidity stability and degradation chemistry of metal halide SSEs investigated by advanced in-situ and operando synchrotron techniques [6-7]. In the end, direct synthesis of halide SSEs on cathode materials by the water-mediated route that has been used to eliminate the interfacial challenges of ASSLBs or act as an interfacial modifier for high-performance all-solid-state Li-O2 batteries will be discussed [8-9].References X. Li, J. Liang, X. Yang, K. R. Adair, C. Wang, F. Zhao, X. Sun, Progress and Perspectives of Halide-based Lithium Conductors for All-Solid-State Lithium Batteries. Energy Environ. Sci., 2020, 13, 1429-1461. J. Liang, X. Li, S. Wang, K. R. Adair, W. Li, Y. Zhao, C. Wang, Y. Hu, L. Zhang, S. Zhao, S. Lu, H. Huang, R. Li, Y. Mo, X. Sun. Site-Occupation-Tuned Superionic LixScCl3+x Halide Solid Electrolytes for All-Solid-State Batteries. J. Am. Chem. Soc., 2020, 142, 7012-7022. X. Li, J. Liang, J. Luo, M. Banis, C. Wang, W. Li, S. Deng, C. Yu, F. Zhao, Y. Hu, T. Sham, L. Zhang, S. Zhao, S. Lu, H. Huang, R. Li, K. R. Adair, X. Sun, Air-stable Li3InCl6 electrolyte with high voltage compatibility for all-solid-state batteries, Energy Environ. Sci., 2019, 12, 2665-2671. C. Yu, Y. Li, K. R. Adair, W. Li, K. Goubitz, Y. Zhao, M. J. Willans, M. A. Thijs, C. Wang, F. Zhao, Q. Sun, S. Deng, J. Liang, X. Li, R. Li, T. Sham, H. Huang, S. Lu, S. Zhao, L. Zhang, L. Eijck, Y. Huang, X. Sun, Tuning ionic conductivity and electrode compatibility of Li3YBr6 for high-performance all solid-state Li batteries, Nano Energy, 2020, 77, 105097. X. Li, J. Liang, N. Chen, J. Luo, K. R. Adair, C. Wang, M. Banis, T. Sham, L. Zhang, S. Zhao, S. Lu, H. Huang, R. Li, X. Sun, Water-Mediated Synthesis of Superionic Halide Solid Electrolyte, Angew. Chem. Int. Ed., 2019, 58, 16427-16432. X. Li, J. Liang, K. R. Adair, J. Li, W. Li, F. Zhao, Y. Hu, T. Sham, L. Zhang, S. Zhao, S. Lu, H. Huang, R. Li, N. Chen, X. Sun, “Origin of Superionic Li3Y1-xInxCl6 Halide Solid-Electrolytes with High Humidity Tolerance” Nano Lett., 2020, 20, 4384-4392. W. Li, J. Liang, M. Li, K. Adair, X. Li, Y. Hu, Q. Xiao, R. Feng, R. Li, L. Zhang, S. Lu, H. Huang, S. Zhao, T. Sham, X. Sun, Unraveling the Origin of Air Stability of Halide Solid-State Electrolytes by In situ and Operando Synchrotron X-ray analytical techniques, Chem. Mater., 2020, 32, 7019–7027. C. Wang, J. Liang, M. Jiang, X. Li, S. Mukherjee, K. Adair, M. Zheng, Y. Zhao, F. Zhao, S. Zhang, R. Li, H. Huang, S. Zhao, L. Zhang, S. Lu, C. Singh, X. Sun, Interface-Assisted In-situ Growth of Halide Electrolytes Eliminating Interfacial Challenges of All-Inorganic Solid-State Batteries. Nano Energy, 2020, 76, 105015. C. Zhao, J. Liang, X. Li, N. Holmes, C. Wang, J. Wang, F. Zhao, S. Li, Q. Sun, X. Yang, J. Liang, X. Lin, W. Li, R. Li, S. Zhao, H. Huang, L. Zhang, S. Lu, X. Sun, Halide-based solid-state electrolyte as an interfacial modifier for high performance solid-state Li–O2 batteries. Nano Energy, 2020, 75, 105036.

Highly conductive polymer electrolytes based on PAN-PEI nanofiber membranes with in situ gelated liquid electrolytes for lithium-ion batteries

The development of solid state electrolytes is considered as an effective approach to build safer lithium-ion batteries by replacing the conventional liquid electrolytes. However, the solid state electrolytes face continuous challenges to improve their ionic conductivities and mechanical properties. Herein, we report the synthesis of novel polymer electrolytes based on cross-linked polyacrylonitrile-polyethylenimine (PAN-PEI) nanofiber membranes infiltrated with in-situ gelated electrolytes using tripropylene glycol diacrylate as crosslinking agent in the organic carbonate-based liquid electrolytes. The PAN-PEI nanofiber membranes with different mass ratios of PAN/PEI prepared by electrospinning method are constructed with entangled nanofibers of an average diameter of ~600 nm. The optimized PAN-PEI based electrolyte has a high ionic conductivity up to 3.39 mS cm−1 at room-temperature and decent tensile strength of 9.36 MPa. Linear sweep voltammetry shows that the polymer electrolyte also has a wide electrochemical window of 5.4 V (vs. Li/Li+). This polymer electrolyte exhibits excellent cycling stability even in the high energy density of LiNi0.8Co0.1Mn0.1O2/Graphite, delivering an initial discharge capacity of 175 mAh g−1 at 0.5 C with a capacity retention of 91.4% after 200 cycles.

Challenges and Development of Composite Solid Electrolytes for All-solid-state Lithium Batteries

All-solid-state lithium batteries are considered to be a new battery system with great development potential and application prospects due to the advantages of high energy density and high security. As a key component of all-solid-state lithium batteries, the development of solid-state electrolytes has received extensive attention in recent years, but most solid electrolytes still exhibit problems, such as low ion conductivity and poor interface compatibility. The design of composite solid-state electrolyte materials with both excellent electrochemical and mechanical properties is an effective way to develop all-solid-state lithium batteries. This review introduces different types of pure component solid electrolytes and analyzes their respective advantages and characteristics firstly. Furthermore, the research progress of composite electrolytes in preparation method, ionic conduction, suppression of lithium dendrites, and the improvement of electrochemical performances are reviewed from the perspective of composite electrolyte structure design, which is to meet different performance requirements. And the future development direction and trend of composite electrolytes are prospected.

Metal Halide Superionic Conductors for All-Solid-State Batteries.

ConspectusRechargeable all-solid-state Li batteries (ASSLBs) are considered to be the next generation of electrochemical energy storage systems. The development of solid-state electrolytes (SSEs), which are key materials for ASSLBs, is therefore one of the most important subjects in modern energy storage chemistry. Various types of electrolytes such as polymer-, oxide-, and sulfide-based SSEs have been developed to date and the discovery of new superionic conductors is still ongoing. Metal-halide SSEs (Li-M-X, where M is a metal element and X is a halogen) are emerging as new candidates with a number of attractive properties and advantages such as wide electrochemical stability windows (0.36-6.71 V vs Li/Li+) and better chemical stability toward cathode materials compared to other SSEs. Furthermore, some of the metal-halide SSEs (such as the Li3InCl6 developed by our group) can be directly synthesized at large scales in a water solvent, removing the need for special apparatus or handling in an inert atmosphere. Based on the recent advances, herein we focus on the topic of metal-halide SSEs, aiming to provide a guidance toward further development of novel halide SSEs and push them forward to meet the multiple requirements of energy storage devices.In this Account, we describe our recent progress in developing metal halide SSEs and focus on some newly reported findings based on state-of-the-art publications on this topic. A discussion on the structure of metal-halide SSEs will be first explored. Subsequently, we will illustrate the effective approaches to enhance the ionic conductivities of metal halide SSEs including the effect of anion sublattice framework, the regulation of site occupation and disorder, and defect engineering. Specifically, we demonstrated that proper structural framework, balanced Li+/vacancy concentration, and reduced blocking effect can promote fast Li+ migration for metal halide SSEs. Moreover, humidity stability and degradation chemistry of metal halide SSEs have been summarized for the first time. Some examples of the application of metal halide SSEs with stability toward humidity have been demonstrated. Direct synthesis of halide SSEs on cathode materials by the water-mediated route has been used to eliminate the interfacial challenges of ASSLBs and has been shown to act as an interfacial modifier for high-performance all-solid-state Li-O2 batteries. Taken together, this Account on metal halide SSEs will provide an insightful perspective over the recent development and future research directions that can lead to advanced electrolytes.

Toward design of cation transport in solid-state battery electrolytes: Structure-dynamics relationships

Cation-conducting, solid-state electrolytes represent a burgeoning focus of battery research, offering the potential for enhanced safety profiles, durability, and wide electrochemical stability windows for high energy density. In this review, we focus primarily on the Li/Na ion conductivity as one of the requirements and limiting factors in development of solid-state electrolytes and secondarily on stability. We highlight experimental and computational methods leading to the current state of understanding of solid-state cation transport, with the goal of drawing out structure-property relationships that lead to design strategies. Topics covered include: descriptors and high-throughput search methodologies including machine learning for identification of fast cation conductors; defect chemistry and its relationship to conduction mechanisms including emerging understanding of frustration, disorder, and concerted ion migration; the impact of strain on transport; factors determining stability; and the role of microstructure and extended defects. We conclude certain sections and the overall review with an outlook for the field, offering ideas for necessary research directions to address knowledge and property gaps.

In situ atomic scale investigation of Li7La3Zr2O12-based Li+-conducting solid electrolyte during calcination growth

The development of solid-state electrolytes (SSEs) is crucial for realizing next-generation high-energy-density and high-safety lithium-ion batteries (LIBs). The chemical composition design and synthesis route are known to be the determining factors for SSE properties. One of the most promising SSEs for LIB applications is garnet-type Li+-conducting oxide synthesized via a solid-state reaction. This study performs an in situ TEM investigation of Li6.25Ga0.25La3Zr2O12 (Ga-LLZO) growth during a high-temperature calcination process. At 750 °C, an intermediate phase, La2Zr2O7 (LZO), is formed through epitaxial growth along the crystallographic orientations of (1‾11)LZO//(1‾11)ZrO2 and [211]LZO//[101]ZrO2. The incorporation of Li and Ga into LZO is found to occur at 900 °C. The LZO transforms into Ga-LLZO via a layer-by-layer diffusion process that takes place along the [011‾] direction. The Ga doping can stabilize the cubic structure of Ga-LLZO at a temperature of 900 °C (while a temperature of >1100 °C is needed to obtain cubic LLZO) and eliminate the formation of the unwanted tetragonal phase. This dynamic microstructure evolution of Ga-LLZO is examined at an atomic scale for the first time. This study opens up a new route to better characterize and understand SSE materials, providing opportunities for further tailoring SSE properties.

(Invited) Challenges of Solid State Electrolytes for High Energy Batteries

The development of solid state electrolytes is very important for future high energy batteries. Among the different strategies, Li metal is a key electrode material for high energy batteries with a specific energy much higher than 300 Wh kg−1. Despite of intensive efforts, significant challenges remain in direct utilization of Li metal anode in realistic high energy cells. This talk will summarize our current understanding of the scientific and technological challenges, discuss recent progress and propose potential directions of solid state electrolytes based on a high-energy cell design, fabrication and testing. The fundamental relationship between the Li anode and other cell components, including all active and inactive materials, is explored at the cell level in order to inspire more new ideas to effectively address the grand challenges in high energy and low cost batteries.

A nanowire-nanoparticle double composite polymer electrolyte for high performance ambient temperature solid-state lithium batteies

Development of solid-state electrolytes that can allow corresponding lithium-ion batteries (LIBs) to perform excellent room temperature cell performance is very meaningful, and also is still a great challenge. One effective measure to solve the above problem is to reduce the interface resistance of the cells via special methods. In this study, a novel double composite polymer electrolyte using polyethylene oxide-polypropylene oxide-polyethylene oxide (PEO-PPO-PEO)/LiTFSI, ceramic nanowires and nanoparticles is designed and prepared (the composite electrolyte is named as CPE) for the first time, which combines the advantages of polymer electrolyte, ceramic nanowires and nanoparticles (different from the related works about only using ceramic nanopartices or ceramic nanowires as fillers). Compared with the composite electrolyte without adding ceramic nanoparticles (named as CPE-0), CPE presents higher ionic conductivity (4.58 × 10−5 S cm−1 at ambient temperature), much higher lithium-ion transference number (0.28), which likely because nanoparticles can promote the formation of more continuous ion channels at the interface of polymer and ceramic fillers. In addition, the CPE shows much wider electrochemical window (5.6 V) than that of the CPE-0 (4.2 V), which can be attributed to the extra nanoparticles can further scavenge trace impurities. Especially, the galvanostatic cycling experiments confirm that CPE has much better stability against Li metal than that of CPE-0, while the Li/CPE/Li symmetric cell also shows a low and stable interface resistance of ∼800 Ω from day 1 to day 25. Therefore, the LiFePO4/Li cell using the CPE shows good cycle performance at 28 °C. Specifically, the cell exhibits a discharge capacity of 154 mAh g−1 with coulombic efficiency of 100% at the 100 cycles. Our work indicates that the interface resistance of the corresponding batteries can be significantly reduced by preparation of CPE with specific polymer electrolytes and ceramic fillers. Thus, the solid-state cells can be well run at ambient temperature.

High-Charge Density Polymerized Ionic Networks Boosting High Ionic Conductivity as Quasi-Solid Electrolytes for High-Voltage Batteries.

Solid-state electrolytes are actively sought for their potential application in energy storage devices, especially lithium metal rechargeable batteries. However, one of the key challenges in the development of solid-state electrolytes is their lower ionic conductivity compared with that of liquid electrolytes (10-2 S cm-1 at room temperature), where a large gap still exists. Therefore, the pursuit of high ionic conductivity equal to that of liquid electrolytes remains the main objective for the design of solid-state electrolytes. Here, we show a series of high-charge density polymerized ionic networks as solid-state electrolytes that take inspiration from poly(ionic liquid)s. The obtained quasi-solid electrolyte slice displays an astonishingly high ionic conductivity of 5.89 × 10-3 S cm-1 at 25 °C (the highest conductivity among those of the state-of-art polymer gel electrolytes and polymer solid electrolytes) and ultrahigh decomposition potential, >5.2 V versus Li/Li+, which are attributed to the continuous ion transport channel formed by an ultrahigh ion density and an enhanced chemical stability endowed by highly cross-linked networks. The Li/LiFePO4 and Li/LiCoO2 batteries (3.0-4.4 V) assembled with the solid electrolytes show high stable capacities of around 155 and 130 mAh g-1, respectively. In principle, our work breaks new ground for the design and fabrication of the solid-state electrolytes in various energy conversion devices.

High-capacity lithium sulfur battery and beyond: a review of metal anode protection layers and perspective of solid-state electrolytes

Li metal has the highest specific capacity (3860 mA h g−1) and the lowest electrochemical potential (− 3.04 V vs. SHE) of available metal anodes. Together with the high specific capacity of sulfur cathodes (1670 mA h g−1), Li metal–S batteries are a promising candidate to achieve high energy density batteries for electric vehicles and future industry. However, Li metal anodes suffer from corrosive reactions with electrolytes, a theoretically infinite volume change, and the growth of dendrites during electrochemical cycling. To realize the practical application of Li metal–S batteries, protective layers or artificial solid-electrolyte interphase (ASEI) layers have been applied to the surface of Li metal. These ASEI layers demonstrate capabilities to suppress the growth of dendrites and mitigate side reactions, which enhance the performance and safety of Li metal anodes in liquid-electrolyte systems, though there are still limitations and challenges. The development of solid-state electrolytes as artificial SEIs provides a promising route to suppress the issues of dendrite formation and the polysulfide “shuttle effect” in Li–S chemistry; however, the improvement in the interfacial compatibility and stability between the Li metal and the solid-state electrolyte is crucially needed. In this review, we summarize different types of ASEI layers used to protect Li metal, especially in Li–S batteries, with both liquid- and solid-electrolyte systems. We also briefly introduce the concept of anode protection of Mg metal and its application in Mg–S batteries. Perspectives regarding the further development and improvement of ASEI layers for Li metal and Mg metal are discussed.

Highly Ion-Conducting New Lithium Halide Solid Electrolytes for Bulk-Type All-Solid-State Batteries

Summary: We find new halide solid electrolyte (HSE) materials that exhibit (a) high lithium ion conductivity, (b) high electrochemical stability against 4-V class cathode materials, and (c) high deformability for low inter-grain resistance realized with facile process. The lithium ionic conductivity of the new HSEs at room temperature reached 0.88 mS/cm. Bulk-type all-solid-state batteries (ASSBs) using these new HSE materials exhibit excellent charge/discharge performance; the initial reversible capacity and coulomb efficiency respectively reached as high as 119 mAh/g and 94 % with LiCoO2 (LCO)-based active cathode material. These HSEs are the first non-sulfide inorganic materials, to our knowledge, that simultaneously satisfy all the above conditions (a) – (c) demanded for realization of all-solid-state batteries (ASSBs) for large capacity applications such as power sources for electric vehicles. In the presentation, we will reveal the details of the constituent elements, the material composition, the crystal structure, the simulated ion conducting path, and the battery characteristics. Introduction: The ASSBs are one of the most promising candidates for the post-lithium ion batteries. Towards realization of its commercialization, one of the key issues is development of solid-state electrolytes. The solid-state electrolytes for ASSBs are imposed to severe demands that need to simultaneously satisfy several requirements: not only high ionic conductivity, but also high deformability (for low inter-grain resistance and facile battery fabrication process), high electrochemical stability, high chemical stability, and viable mass production process, etc. Currently sulfides1 and oxides2 are the most widely studied/employed electrolytes for ASSB studies, and several other material systems3,4 have also been proposed. It is, however, still challenging to satisfy all the above requirements at the same time, and discovery of alternative lithium ion conductors are expected. We focus on halide materials as a solid electrolyte for ASSB application due to their advantageous natures; the halide ions are monovalent, fairly large ionic radii, high polarizability, high electrochemical oxidation stability, and high chemical stability of halide ionic materials against oxygen. Nevertheless, only several halide materials have been explored as lithium ion conductors so far, much less its use for ASSBs. We here report on our finding of the new halide lithium ion conductors and their use for bulk-type ASSBs. Experiments, results and discussions: The ionic conductivities of the HSE materials were measured on pressed pellets using electrochemical impedance spectroscopy (EIS). The conductivities at room temperature (at 25 °C) and its activation energies were, respectively, σ = 0.52 mS/cm and E a = 0.40 eV for chloride HSE and σ = 0.88 mS/cm and E a = 0.36 eV for bromide HSE. Their DC conductivities measured with Li – HSE – Li configuration were identical to the AC conductivities measured with blocking electrodes, SUS – HSE – SUS. The electromotive force generated by Li – HSE – LiIn cell was consistent with the value expected from Nernst equation (= 0.61 V). These electrochemical characterizations undoubtedly revealed that the dominant electric carrier of these HSEs is lithium ions. We note that all the above measurements were done on pellets formed by simply pressing powders of the HSEs, which indicate high deformability and low inter-grain resistance of these newly synthesized HSE materials. The ASSBs using these HSE materials showed excellent charge/discharge performance using LiCoO2 as a cathode material and Li-In alloy as an anode material. The bulk-type ASSBs were assembled based on the HSE powders, LiCoO2 powders and Li-In alloy foil, simply by pressing them without any heat treatment. The characteristic plateau of the redox reaction of Li1-xCoO2 was clearly observed in the charge/discharge curves. The initial charged capacity reached 126 mAh/g (~ 93 % of the theoretical capacity) and the discharge capacity was 119 mAh/g, resulting in the coulomb efficiency for the first cycle as high as 94.4 %. The coulomb efficiency for the subsequent cycles were higher than 99 % till the measurement terminated at 12th cycle. Such high coulomb efficiency is a manifestation of the high electrochemical stability of these HSE materials against 4-V class cathode materials. All of the above characteristics of the HSEs clearly indicates that HSEs can be one of the candidate materials for bulk-type ASSBs. They show not only high lithium ion conductivity, but also showed excellent battery performance with bulk-type ASSBs with high oxidation stability. 1 Y. Kato et al., Nat. Energy, 1, 16030 (2016). 2 X. Han et al, Nature Materials 16, 572–579 (2017). 3 M. H. Braga et al, J. Mater. Chem. A, 2, 5470 (2014). 4 H. Maekawa et al, J. Am. Chem. Soc. 131, 894–895 (2009).