Inorganic Solid-state Electrolytes Research Articles

A robust 3D nanostructured composite polymer electrolyte with novel dual-ion channels toward solid-state sodium metal batteries

The high energy density and low cost of sodium metal batteries enable them to be the rising star of next-generation batteries. However, the growth of sodium dendrites and the high activity of sodium metal may lead to significant safety risks for liquid sodium metal batteries. Composite polymer electrolytes (CPEs), which combine the advantages of inorganic solid-state electrolyte and solid-state polymer electrolytes, have become a promising candidate to replace liquid electrolytes. In this study, a novel Na-beta-Al2O3/polyacrylonitrile (PAN) CPE with a 3D network nanostructure (NAP) has been synthesized by electrospinning method. NAP membrane provides synergistic dual-ion channels for the migration of sodium ions, exhibiting ionic conductivity of 7.22 × 10−4 S cm−1, a sodium-ion transport number of 0.73, and an electrochemical stabilization window as high as 4.92 V. Compared with pure PAN, NAP presents enhanced mechanical strength, superior electrochemical properties and interfacial stability. NAP-based sodium symmetric cell achieves stable plating and stripping for 800 h. At room temperature, the capacity retention ratios of NAP-based Na3V2(PO4)3//Na cell are 92.02 % (0.2C, 200 cycles) and 73.10 % (0.5C, 1000 cycles), respectively. The capacity retention is 72.49 % after 250 cycles at 0.5C and a high temperature of 60 ℃. X-ray photoelectron spectroscopy spectra indicate that solid electrolyte interphase formed in NAP-based battery contains higher NaF component, R–(CO)O–Na content and interfacially favorable organic components, which are beneficial to accelerate the sodium-ion transfer at the interface. This work provides new insights into the construction of 3D nanostructured CPEs with fast ion transport for solid-state sodium metal batteries.

Development of High-Performance Cathodes for Inorganic Halide All-Solid-State Li-Ion Batteries

Electric vehicles (EVs), representing the future of transportation, are predicted to be one of the ultimate solutions to eliminate greenhouse gas emissions. Li-ion batteries (LIBs), as the most promising sustainable energy devices, are critical for the development of EVs because of their higher operating voltages compared to other energy storage technologies. However, the development of conventional LIBs touched the ceiling because of three main challenges. (1) The use of flammable and toxic liquid electrolytes brings high safety risks. (2) The limited energy density of LIBs cannot satisfy the requirement for long-range EVs. (3) The increasing market demand for LIBs will cause resource shortage and rise of cost.[1] Accordingly, all-solid-state Li-ion batteries (ASSLIBs) have recently emerged as promising alternative batteries for next-generation EVs because of their ability to overcome the drawbacks of conventional LIBs. Among the developed solid-state electrolytes (SSEs), inorganic SSEs (e.g., sulfide SSEs, halide SSEs) have high Li+ conductivity at 10-3 S cm-1 and improved interfacial stability, demonstrating stable cycling performance in ASSLIBs.[2] However, inorganic ASSLIBs still face some key challenges hindering their application in EVs. For example, the rate capability of inorganic ASSLIBs still falls far below the requirements of fast-charging EVs (full-charged in 15 min). In addition to the effect of Li+ conductivity in SSEs, Li+/e- transfer kinetics at the cathode interface and in cathode materials are also critically important for the high-rate capability of inorganic ASSLIBs. In this talk, I will first review our previous studies on cathode interface in inorganic ASSLIBs.[3-7] After that, I will introduce our most recent research on unveiling the kinetic limitation of cathode interfaces in inorganic ASSLIBs by synchrotron-based spectromicroscopy. Our research suggests that poor Li+/e- transfer kinetics at the cathode/SSE interface and in the cathode bulk structure are the key limitation for the low capacity of inorganic ASSLIBs under high-rate charge-discharge cycles.

Understanding the influence of local structure distortions on Na-ion migration in perovskite solid electrolytes

The perovskite structured oxides of composition ABO3 are considered strong candidates for solid-state electrolytes in all-solid-state batteries due to their chemical and structural flexibility. However, further improvements must be made before they become commercially viable, and this requires a clear understanding of the structure-property relationships. In this study, the local structure of the perovskite sodium-ion solid electrolyte series Na1/2−xLa1/2−xSr2xZrO3 (NLSZ, x = 14, 16, 18, 116) was investigated via neutron total scattering. Small-box modelling against the neutron pair distribution function with the orthorhombic Pbnm structure showed local-scale features that deviate from the average structure. Big-box modelling revealed significant differences between the bonding configurations of the different A-site cations, which impacts the ionic conductivity of the material. This study demonstrates how understanding local-scale disorder is important for tuning the structure-property relationships of inorganic solid-state electrolyte materials in sustainable battery technologies.

Generalized Interphase Design for Stabilized Li/Inorganic Electrolyte Interfaces

AbstractAll‐solid‐state Li metal batteries (ASSLMBs) using inorganic solid‐state electrolytes (ISEs) are considered promising energy storage technologies owing to their intrinsic safety and high energy density. Nevertheless, one critical challenge confronting ASSLMBs is the inability of the ISEs to prevent Li dendrite growth, which has not yet been fully addressed. Herein, general design principles of artificial solid electrolyte interphases (ASEI) for suppressing Li dendrites in ASSLMBs are proposed by systematically exploring the formation mechanism of Li dendrites. Subsequently, a tailored LiF‐Li3N ASEI is constructed to inspect the Li‐dendrite‐free design principles. The LiF‐Li3N modified Li (LFN‐Li) can effectively inhibit the side reactions and suppress the growth of Li dendrites, thus boosting the critical current densities of Li10GeP2S12 (LGPS) to a record‐high value of 3.4 mA cm−2. Furthermore, the LFN‐Li/LGPS/LFN‐Li can cycle stably for over 5000 h at 0.2 mA cm−2. Crucially, the versatility of the designed ASEI is highlighted as it ensures outstanding long‐term stability in symmetric cells featuring oxide Li1.3Al0.3Ti1.7(PO)3 or halide Li2ZrCl6 ISEs. As a result, the ASEI enables LiNi0.8Mn0.1Co0.1O2/LGPS/LFN‐Li and FeS2/LGPS/LFN‐Li cells to achieve high discharge‐specific capacities and desirable cyclic stability at room temperature. The generalized ASEI design principles rationalize the development of high‐energy ASSLBMs.

Synergistic nanocomposite polymer electrolytes for advanced all-solid-state sodium-ion batteries

Polymer solid composite electrolyte (PSCE) has gained significant attention due to its superior ion conductivity and compatibility with electrodes compared to inorganic solid-state electrolytes, as well as its better safety compared to liquid electrolytes. In this study, Na3Zr2Si2PO12 (NZSP) nanoparticles are synthesized with polyethylene oxide (PEO) and sodium percarbonate (SPC)-based PSCE. The resulting material is evaluated for its application performances in all-solid-state sodium-ion batteries (ASSBs). The addition of Na3Zr2Si2PO12 filler reduces the polymer matrix's crystallinity and decreases the formation of sodium dendrites. As a result, the PSCE delivers an enlarged electrochemical window stability of 4.8 V and improved ion conductivity that can reach as high as 2.6 × 10−4 SCm−1. When applied in ASSBs, the resulting PSCE shows a high first discharge capacity of 75.4 mAh g−1 at 0.2C and a promising faradaic efficiency of 97% (for 100 cycles). These results indicate that PEO−SPC−NZSP based PSCE can be significantly improved by adding Na3Zr2Si2PO12 filler, thus enabling its practical application as a form of energy storage.

Rapid Mining of Fast Ion Conductors via Subgraph Isomorphism Matching.

The rapidly evolving field of inorganic solid-state electrolytes (ISSEs) has been driven in recent years by advances in data-mining techniques, which facilitates the high-throughput computational screening for candidate materials in the databases. The key to the mining process is the selection of critical features that underline the similarity of a material to an existing ISSE. Unfortunately, this selection is generally subjective and frequently under debate. Here we propose a subgraph isomorphism matching method that allows an objective evaluation of the similarity between two compounds according to the topology of the local atomic environment. The matching algorithm has been applied to discover four structure types that are highly analogous to the LiTi2(PO4)3 NASICON prototype. We demonstrate that the local atomic environments similar to LiTi2(PO4)3 endow these four structures with favorable Li diffusion tunnels and ionic conductivity on par with those of the prototype. By further taking into account the electronic structure and electrochemical stability window, 13 compounds are identified to be potential ISSEs. Our findings not only offer a promising approach toward rapid mining of fast ion conductors without limitation in the compositional range but also reveal insights into the design of ISSEs according to the topology of their framework structures.

A Universal Self-Propagating Synthesis of Aluminum-Based Oxyhalide Solid-State Electrolytes.

Inorganic solid-state electrolytes (SSEs) play a vital role in high-energy all-solid-state batteries (ASSBs). However, the current method of SSE preparation usually involves high-energy mechanical ball milling and/or a high-temperature annealing process, which is not suitable for practical application. Here, a facile strategy is developed to realize the scalable synthesis of cost-effective aluminum-based oxyhalide SSEs, which involves a self-propagating method by the exothermic reaction of the raw materials. This strategy enables the synthesis of various aluminum-based oxyhalide SSEs with tunable components and high ionic conductivities (over 10-3 S cm-1 at 25 °C) for different cations (Li+, Na+, Ag+). It is elucidated that the amorphous matrix, which mainly consists of various oxidized chloroaluminate species that provide numerous sites for smooth ion migration, is actually the key factor for the achieved high conductivities. Benefit from their easy synthesis, low cost, and low weight, the aluminum-based oxyhalide SSEs synthesized by our approach could further promote practical application of high-energy-density ASSBs.

Incorporating Sodium-Conductive Polymeric Interfacial Adhesive with Inorganic Solid-State Electrolytes for Quasi-Solid-State Sodium Metal Batteries.

Inorganic solid-state electrolytes have attracted enormous attention due to their potential safety, increased energy density, and long cycle-life benefits. However, their application in solid-state batteries is limited by unstable electrode-electrolyte interface, poor point-to-point physical contact, and low utilization of metallic anodes. Herein, interfacial engineering based on sodium (Na)-conductive polymeric solid-state interfacial adhesive is studied to improve interface stability and optimize physical contacts, constructing a robust organic-rich solid electrolyte interphaselayer to prevent dendrite-induced crack propagation and security issues. The interfacial adhesive strategy significantly increases the room-temperature critical current density of inorganic Na-ion conductors from 0.8 to 3.2mAcm-2 and markedly enhances the cycling performance of solid-state batteries up to 500 cycles, respectively. Particularly, the Na3V2(PO4)3-based full solid-state batteries with high cathode loading of 10.16mgcm-2 also deliver an excellent cycling performance, further realizing the stable operation of solid-state laminated pouch cells. The research provides fundamental perspectives into the role of interfacial chemistry and takes the field a step closer to realizing practical solid-state batteries.

Stable Oxyhalide-Nitride Fast Ionic Conductors for All-Solid-State Li Metal Batteries.

Rechargeable all-solid-state lithium metal batteries (ASSLMBs) utilizing inorganic solid-state electrolytes (SSEs) are promising for electric vehicles and large-scale grid energy storage. However, the Li dendrite growth in SSEs still constrains the practical utility of ASSLMBs. To achieve a high dendrite-suppression capability, SSEs must be chemically stable with Li, possess fast Li transfer kinetics, and exhibit high interface energy. Herein, a class of low-cost, eco-friendly, and sustainable oxyhalide-nitride solid electrolytes (ONSEs), denoted as LixNyIz-qLiOH (where x = 3y + z, 0 ≤ q ≤ 0.75), is designed to fulfill all the requirements. As-prepared ONSEs demonstrate chemically stable against Li and high interface energy (>43.08 meV Å-2), effectively restraining Li dendrite growth and the self-degradation at electrode interfaces. Furthermore, improved thermodynamic oxidation stability of ONSEs (>3V vs Li+/Li, 0.45V for pure Li3N), arising from the increased ionicity of Li─N bonds, contributes to the stability in ASSLMBs. As a proof-of-concept, the optimized ONSEs possess high ionic conductivity of 0.52 mS cm-1 and achieve long-term cycling of Li||Li symmetric cell for over 500h. When coupled with the Li3InCl6 SSE for high-voltage cathodes, the bilayer oxyhalide-nitride/Li3InCl6 electrolyte imparts 90% capacity retention over 500 cycles for Li||1 mAh cm-2 LiCoO2 cells.

Constructing Enhanced Composite Solid-State Electrolytes with Sb/Nb Co-Doped LLZO and PVDF-HFP

Composite solid-state electrolytes are viewed as promising materials for solid-state lithium-ion batteries due to their combined advantages of inorganic solid-state electrolytes and solid-state polymer electrolytes. In this study, the solid electrolytes Li6.7−xLa3Zr1.7−xSb0.3NbxO12 (LLZSNO) with Sb and Nb co-doping were prepared by a high-temperature solid-phase method. Results indicate that Sb/Nb co-doping causes lattice deformation in LLZO and increases the lithium vacancy concentration and conductivity of LLZO. Then, with the co-doped LLZSNO as an inorganic filler, a composite solid electrolyte of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) was prepared with a casting method. The obtained composite solid electrolyte exhibits a high ionic conductivity of 1.76 × 10−4 S/cm at room temperature, a wide electrochemical stable window of 5.2 V, and a lithium-ion transfer number of 0.32. The Li|LiFePO4 coin battery with the composite solid electrolyte shows a high specific capacity of 161.2 mAh/g and a Coulombic efficiency close to 100% at 1 C. In addition, the symmetrical lithium battery Li|Li with the composite electrolyte could cycle stably for about 1500 h without failure at room temperature.

Computational Design of Inorganic Solid-State Electrolyte Materials for Lithium-Ion Batteries

Computational Design of Inorganic Solid-State Electrolyte Materials for Lithium-Ion Batteries

How Concerted Are Ionic Hops in Inorganic Solid-State Electrolytes?

Despite being fundamental to the understanding of solid-state electrolytes (SSEs), little is known on the degree of coordination between mobile ions in diffusive events, thus hindering a detailed comprehension and possible rational design of SSEs. Here, we introduce an unsupervised k-means clustering approach that is able to identify ion-hopping events and correlations between many mobile ions and apply it to a comprehensive ab initio MD database comprising several families of inorganic SSEs and millions of ionic configurations. It is found that despite two-body interactions between mobile ions being the largest, higher-order n-ion (2 < n) correlations are most frequent. Specifically, we prove a general exponential decaying law for the probability density function governing the number of concerted mobile ions. For the particular case of Li-based SSEs, it is shown that the average number of correlated mobile ions amounts to 10 ± 5 and that this result is practically independent of the temperature. Interestingly, our data-driven analysis reveals that fast-ionic diffusion strongly and positively correlates with ample hopping lengths and long hopping spans but not with high hopping frequencies and short interstitial residence times. Finally, it is shown that neglection of many-ion correlations generally leads to a modest overestimation of the hopping frequency that roughly is proportional to the average number of correlated mobile ions.

NaSbF4 nanoparticles as solid-state electrolytes in sodium-iodine batteries: sodium ion transport via conversion reaction and shuttle effect retarded by fluoride

Na-I2 batteries have emerged as an appealing energy storage technology owing to high energy density and cost-effectiveness. However, the practical application of Na-I2 batteries faces the dissolution of iodide/polyiodide in the electrolyte during the charge/discharge process. Herein, we immobilize I2 by utilization of NaSbF4 (NSF)-based solid-state electrolyte (SSE). Impressively, the Na+ transport in NSF nanoparticles (NPs) is via the conversion reaction of NaSbF4 + NaF ↔ Na2SbF5, which is different from the acknowledged Na+ diffusion mechanism via vacancies in inorganic SSEs. To improve the interfacial compatibility, a composite polymer electrolyte (CPE) is fabricated based on NSF, poly (vinylidene fluoride - hexafuoro -propylene) (PVDF-HFP) and NaClO4, giving rise to stable Na stripping/plating in Na|Na symmetric cell. Especially, the quasi-solid-state Na|NSF CPE |I2 full cell shows an outstanding electrochemical behavior, which is associated with the partial reduction of ClO4− → Cl− and the stabilization of I+ by F− or Cl− in the charge/discharge process. The resultant I+-F- or I+-Cl- intermediate can promote the multi-electron transfer of 2I− → I2 → 2I+, leading to enhanced capacity and mitigated shuttle effect of iodide. Meanwhile, the formation of I+-F- in turn weakens the interaction of Na⋯F in NSF, which is beneficial for Na+ transport.

Enhancement of microstructure and electrochemical properties of LLZTO solid state electrolyte by co-doping with Ga and Y

Recently, there has been strong interest in inorganic solid-state electrolytes for all-solid-state batteries, among which the garnet electrolyte LLZO has attracted much attention due to its excellent properties, such as high ionic conductivity and broad electrochemical stability. The aim of our study was to improve the performance of Ta-doped LLZO (LLZTO) by co-doping Ga and Y at the Li and La sites using conventional solid-phase synthesis methods. We thoroughly investigated how Ga and Y affect the microstructure and electrochemical properties of LLZTO. The results show that the relative density of Ga- and Y-doped LLZTO increases significantly up to 94% under the same sintering conditions. This doping resulted in a significant increase in ionic conductivity from 2.0 × 10−4 S·cm−1 to 1.05 × 10−3 S·cm−1 and a decrease in electronic conductivity from 2.16 × 10−7 S·cm−1 to 9.18 × 10−8 S·cm−1. Subsequently, the symmetric cells were assembled and tested, and it was found that the interfaces of the doped solid-state electrolytes were much more stable and that the cycling time was longer. Thus, our study successfully coordinated the co-doping of Ga, Y, and Ta, providing valuable insights for the subsequent production of LLZO materials with higher densities and better performance. This study is a promising step toward the realization of safer all-solid-state batteries with higher energy densities.

NaSn2F5 nanocluster composed of nanoparticles with matched lattices induced by dislocations: Accelerated sodium-ion transport via in situ oxidation in solid-state sodium metal battery

Na metal batteries using inorganic solid-state electrolytes (SSEs) have attracted extensive attention due to their superior safety and high energy density. However, their development is plagued by the unclear structural/volumetric evolution of SSEs and the corresponding Na+ migration mechanisms. In this work, NaSn2F5 (NSF) clusters are composed of nanoparticles (NPs) with matched lattices induced by dislocations, which can mitigate the volume swelling/shrinkage of the NPs. NSF behaves like a single ion conductor with a high Na+ transference number (tNa+) of 0.79. Specially, the ionic conductivity (σ) of NSF is increased from 7.64 × 10-6 to 5.42 × 10-5 S cm−1 after partial irreversible oxidation of Sn2+ (0.118 Å) → Sn4+ (0.069 Å) with the shrunk ionic radius during the charge process, giving more spaces for Na+ migration. Furthermore, a poly(acrylonitrile)-NaSn2F5-NaPF6 composite polymer electrolyte (NSF CPE) was fabricated with a σ of 4.13 × 10-4 S cm−1 and a tNa+ of 0.60. The NSF CPE-based symmetric cell can operate over 3000 h due to the couplings between the different components in NSF CPE, which is beneficial for ion transfer and the construction of stable solid electrolyte interface. And the quasi-solid-state Na|NSF CPE|Na3V2(PO4)3 full cell displays excellent electrochemical performance.

Chemomechanical Origins of the Dynamic Evolution of Isolated Li Filaments in Inorganic Solid-State Electrolytes.

The penetrating growth of Li into the inorganic solid-state electrolyte (SSE) is one key factor limiting its practical application. Research to understand the underlying mechanism of Li penetration has been ongoing for years and is continuing. Here, we report an in situ scanning electron microscopy methodology to investigate the dynamic behaviors of isolated Li filaments in the garnet SSE under practical cycling conditions. We find that the filaments tend to grow in the SSE, while surprisingly, those filaments can self-dissolve with a decrease in the current density without a reversal of the current direction. We further build a coupled electro-chemo-mechanical model to assess the interplay between electrochemistry and mechanics during the dynamic evolution of filaments. We reveal that filament growth is strongly regulated by the competition between the electrochemical driving force and mechanical resistive force. The numerical results provide rational guidance for the design of solid-state batteries with excellent properties.

Self-assembled hydrated copper coordination compounds as ionic conductors for room temperature solid-state batteries

As the core component of solid-state batteries, neither current inorganic solid-state electrolytes nor solid polymer electrolytes can simultaneously possess satisfactory ionic conductivity, electrode compatibility and processability. By incorporating efficient Li+ diffusion channels found in inorganic solid-state electrolytes and polar functional groups present in solid polymer electrolytes, it is conceivable to design inorganic-organic hybrid solid-state electrolytes to achieve true fusion and synergy in performance. Herein, we demonstrate that traditional metal coordination compounds can serve as exceptional Li+ ion conductors at room temperature through rational structural design. Specifically, we synthesize copper maleate hydrate nanoflakes via bottom-up self-assembly featuring highly-ordered 1D channels that are interconnected by Cu2+/Cu+ nodes and maleic acid ligands, alongside rich COO− groups and structural water within the channels. Benefiting from the combination of ion-hopping and coupling-dissociation mechanisms, Li+ ions can preferably transport through these channels rapidly. Thus, the Li+-implanted copper maleate hydrate solid-state electrolytes shows remarkable ionic conductivity (1.17 × 10−4 S cm−1 at room temperature), high Li+ transference number (0.77), and a 4.7 V-wide operating window. More impressively, Li+-implanted copper maleate hydrate solid-state electrolytes are demonstrated to have exceptional compatibility with both cathode and Li anode, enabling long-term stability of more than 800 cycles. This work brings new insight on exploring superior room-temperature ionic conductors based on metal coordination compounds.

Heteroatom-based doping and neutron diffraction: doping strategies and mechanisms for ionic conductivity enhancement in inorganic solid-state electrolytes

Exploring doping fundamentals to boost inorganic SSEs, we detail their application in various electrolytes, highlighting neutron diffraction's role in revealing microstructural and lithium-ion distribution effects.

Theoretical calculations and simulations power the design of inorganic solid-state electrolytes.

Using solid-state electrolytes (SSEs) to build batteries helps improve the safety and lifespan of batteries, making it crucial to deeply understand the fundamental physical and chemical properties of SSEs. Theoretical calculations based on modern quantum chemical methods and molecular simulation techniques can explore the relationship between the structure and performance of SSEs at the atomic and molecular levels. In this review, we first comprehensively introduce theoretical methods used to assess the stability of SSEs, including mechanical, phase, and electrochemical stability, and summarize the significant progress achieved through these methods. Next, we outline the methods for calculating ion diffusion properties and discuss the advantages and limitations of these methods by combining the diffusion behaviors and mechanisms of ions in the bulk phase, grain boundaries, and electrode-solid electrolyte interfaces. Finally, we summarize the latest research progress in the discovery of high-quality SSEs through high-throughput screening and machine learning and discuss the application prospects of a new mode that incorporates machine learning into high-throughput screening.

A comprehensive investigation of Ag7P3X11 (X = {O, S, and Se}) solid-state silver superionic conductors

This investigation rigorously analyzes and introduces a new class of high-performance inorganic solid-state electrolytes, formulated as Ag7P3X11 (X = {O, S, Se}), through comprehensive ab initio calculations, highlighting their potential for advanced energy storage technologies.