Electrolytes For Solid-state Batteries Research Articles

Temperature-dependent compatibility study on halide solid-state electrolytes in solid-state batteries.

All-solid-state lithium batteries (ASSLBs) have attracted much attention owing to their high safety and energy density compared to conventional organic electrolytes. However, the interfaces between solid-state electrolytes and electrodes retain some knotty problems regarding compatibility. Among the various SSEs investigated in recent years, halide SSEs exhibit relatively good interfacial compatibility. The temperature-dependent interfacial compatibility of halide SSEs in solid-state batteries is investigated by thermal analysis using simultaneous thermogravimetry and differential scanning calorimetry (TG–DSC) and X-ray diffraction (XRD). Halide SSEs, including rock-salt-type Li3InCl6 and anti-perovskite-type Li2OHCl, show good thermal stability with oxides LiCoO2, LiMn2O4, and Li4Ti5O12 up to 320 °C. Moreover, anti-perovskite-type Li2OHCl shows a chemical reactivity with other battery materials (eg., LiFePO4, LiNi0.8Co0.1Mn0.1O2, Si-C, and Li1.3Al0.3Ti1.7(PO4)3) at 320°C, which reaches the melting point of Li2OHCl. It indicated that Li2OHCl has relatively high chemical reactivity after melting. In contrast, rock-salt-type Li3InCl6 shows higher stability and interfacial compatibility. This work delivers insights into the selection of suitable battery materials with good compatibility for ASSLBs.

Fundamental investigations on the sodium-ion transport properties of mixed polyanion solid-state battery electrolytes

Lithium and sodium (Na) mixed polyanion solid electrolytes for all-solid-state batteries display some of the highest ionic conductivities reported to date. However, the effect of polyanion mixing on the ion-transport properties is still not fully understood. Here, we focus on Na1+xZr2SixP3−xO12 (0 ≤ x ≤ 3) NASICON electrolyte to elucidate the role of polyanion mixing on the Na-ion transport properties. Although NASICON is a widely investigated system, transport properties derived from experiments or theory vary by orders of magnitude. We use more than 2000 distinct ab initio-based kinetic Monte Carlo simulations to map the compositional space of NASICON over various time ranges, spatial resolutions and temperatures. Via electrochemical impedance spectroscopy measurements on samples with different sodium content, we find that the highest ionic conductivity (i.e., about 0.165 S cm–1 at 473 K) is experimentally achieved in Na3.4Zr2Si2.4P0.6O12, in line with simulations (i.e., about 0.170 S cm–1 at 473 K). The theoretical studies indicate that doped NASICON compounds (especially those with a silicon content x ≥ 2.4) can improve the Na-ion mobility compared to undoped NASICON compositions.

Opportunities for halide solid electrolytes in solid-state batteries

Opportunities for halide solid electrolytes in solid-state batteries

Interplay of Dynamic Constriction and Interface Morphology between Reversible Metal Anode and Solid Electrolyte in Solid State Batteries.

In an all-solid-state battery, the electrical contact between its individual components is of key relevance in addition to the electrochemical stability of its interfaces. Impedance spectroscopy is particularly suited for the non-destructive investigation of interfaces and of their stability under load. Establishing a valid correlation between microscopic processes and the macroscopic impedance signal, however, is challenging and prone to errors. Here, we use a 3D electric network model to systematically investigate the effect of various electrode/sample interface morphologies on the impedance spectrum. It is demonstrated that the interface impedance generally results from a charge transfer step and a geometric constriction contribution. The weights of both signals depend strongly on the material parameters as well as on the interface morphology. Dynamic constriction results from a non-ideal local contact, e.g., from pores or voids, which reduce the electrochemical active surface area only in a certain frequency range. Constriction effects dominate the interface behavior for systems with small charge transfer resistance like garnet-type solid electrolytes in contact with a lithium metal electrode. An in-depth analysis of the origin and the characteristics of the constriction phenomenon and their dependence on the interface morphology is conducted. The discussion of the constriction effect provides further insight into the processes at the microscopic level, which are, e.g., relevant in the case of reversible metal anodes.

Optimization of Catholyte in Composite Cathodes for Garnet-Structured Llzo Electrolyte in Solid-State Batteries

The application of Li-ion batteries have been expanding at a rapid rate in recent decades due to the tremendous demands in the market for portable electronics, smart grid, and electric vehicles (EVs). All-solid-state lithium metal battery (ASSLB) is the most promising next-generation energy storage device as they can solve the safety issue resulted from liquid electrolytes.Among different types of solid-state electrolytes (SSE), garnet-type structure materials have been shown to be very promising for the development of ASSLBs owing to their high Li-ion conductivity (∼10–3 S cm–1 at RT), wide electrochemical stability window (∼6 V vs Li+/Li), and good chemical stability against Li metal. The high interfacial resistance generated by inadequate contact and interfacial reactions is a substantial impediment to the adaptation of ASSLBs. To address this challenge, a catholyte (a small amount of ionic conductors which are mostly derived from the solid electrolyte formulation) is introduced into the cathode formulation. This necessities a re-design of the cathode into a composite cathode with possibly new components such as carbon additives with high aspect ratio and conductive binders. Understanding their individual and combined impacts on performance is essential in the pursuit of optimized systems.In this work, we designed a series of composite cathode formulations defined with three cathode active materials (LFP, NMC 622 and NMC 811), three carbonaceous additives (carbon black, carbon nanofibers and carbon nanotubes), and a series of organic and inorganic molecular, and polymeric conductors along with LLZO to create a composite cathode with high capacity and stability at high C-rates. A systematic DOE approach has been utilized to evaluate the impact of each component on the electrode and cell performance and the results will be presented.

Improved Air Stability of Sulfide Electrolytes for All-Solid-State Li Batteries

Sulfide-based solid electrolytes (SEs) are receiving increasing attention due to their high ionic conductivities (up to 10-2 S cm-1 at room temperature) that can be comparable to the liquid electrolytes.1 However, the air stability of sulfide SEs is very poor.2, 3 Most developed sulfide SEs are prone to turn bad when exposed to the moisture. The generated H2S is dangerous, which places the commercialization of sulfide SEs into a challenging situation. 2, 3 In our work, to improve the air stability of sulfide SEs, we employed element substitution (Sn and Sb) for the problematic element (P) in conventional sulfide SEs (Li3PS4, Li6PS5I, Li10GeP2S12) based on the hard and soft acid and base theory (HSAB).4, 5, 6 Our results suggest that Sn and Sb-substituted sulfide SEs show significantly improved air stability compared with the pristine sulfides. Meanwhile, it is found that the Sn or Sb element substitution effectively enhance the ionic conductivity as well as Li metal compatibility in some cases. Various structural (e.g., X-ray diffraction, X-ray absorption near edge spectroscopy, solid-state nuclear magnetic resonance) and electrochemical characterizations are employed to identify the mechanism of the improvements are related to the Sn/Sb substitution-derived crystal structure, reinforced bonding energy, and the optimized electrode/electrolyte interfaces. Our studies provide a new idea of designing functional sulfide composition to realize improved air stability coupling with other essential properties. Re ferences N. Kamaya, R. Kanno*, et al. A lithium superionic conductor, Nat. Mater. 2011, 10, 682-686.C. Yu, F. Zhao, J. Luo, X. Sun*. Recent Development of lithium argyrodite solid-state electrolytes for solid-state batteries: synthesis, structure, stability and dynamics. Nano Energy 2021, 83, 105858.F. Zhao, S. Zhang, Y. Li*, X. Sun*. Emerging characterization techniques to understand electrode interfaces in all-solid-state lithium batteries. Small Struct. 2021, DOI: 10.1002/sstr.202100146.F. Zhao, J. Liang, X. Sun*, et al. A Versatile Sn-Substituted Argyrodite Sulfide Electrolyte for All-Solid-State Li Metal Batteries, Adv. Energy Mater. 2020, 10, 1903422.F. Zhao, X. Sun*, et al. An Air-Stable and Li-Metal-Compatible Glass-Ceramic Electrolyte enabling High-Performance All-Solid-State Li-Metal Batteries. Adv. Mater. 2021, 33, 2006577.J. Liang, X. Sun*, et al. Li10Ge(P1–xSbx)2S12 Lithium-Ion Conductors with Enhanced Atmospheric Stability, Chem. Mater. 2020, 32, 2664-2672.

Lithium phosphosulfide electrolytes for solid-state batteries: Part I

A high performance and stable Li-ion conductive solid electrolyte is one of the key components for the future all-solid-state batteries with metallic lithium anodes. Phosphate, oxide and phosphosulfide-based inorganic solid electrolytes are currently under development. High ambient temperature Li-ion conductivities amounting up to 10[Formula: see text] S cm[Formula: see text] for the best performing electrolytes distinguish the phosphosulfides from the other material systems. Part I of the review starts with the motivation and background for the development of Li-phosphosulfide electrolytes followed by an overview of four different types of phosphosulfide electrolytes; the Li–P–S, thio-LiSICon, LGPS and the Argyrodite-type electrolytes. The core of part I is concerned with a detailed discussion of the phosphosulfide electrolyte types that have been under investigation already for a long time, the Li–P–S and the LiSICon. There is a multiplicity of different compositions within each of these types. The idea behind the outline of these sections is to point out the relations and differences between the different materials with respect to their chemistry related to the phase diagrams. Patterns for the relations among the materials identified in the phase diagrams are the base for a discussion of structure, processing and Li-ion conductivity within separate sections for each type and resulting in intra-type comparisons. The follow up part II will continue with a treatment of the more recently developed LGPS and Argyrodite-type electrolytes tracking the same concept, before addressing an inter-type comparison of ambient temperature Li-ion conductivities and the electrochemical stability of the electrolytes vs. metallic lithium. A final section in part II summarizes conclusions and provides perspectives for future research on Li-ion conductive phosphosulfide electrolytes.

Coordination Li diffusion chemistry in NASICON Li1.5Al0.5Ge1.5(PO4)3 solid electrolyte

The NASICON Al-doped LiGe2(PO4)3 (Li1.5Al0.5Ge1.5(PO4)3: LAGP) is one of the promising solid electrolytes that is intensively optimized in solid-state Li-ion batteries. However, its underlying fast Li-ion diffusion kinetic has not been fully understood yet. In this context, density functional theory (DFT) calculations were performed to comprehend the Li-ion migration behaviors in LAGP, especially under the emergence of metastable interstitial sites by the doped Al-ions to transform the Li-ion migration to an interlaced interstitial and multi-ionic concerted hopping mechanisms. The sluggish lattice 6b Li-ion are driven to accelerate and itinerate by the strong Coulombic repulsion of 36f Li-ions in the LAGP lattice. Moreover, the Li-ion migration energy barrier further decreases for the LAGP with Li/Al antisite, which, however, could also deteriorate the conducting performance with the amount increasing to a critical value. These important findings uncover the regulation of metastable sites in the inter-connected channels that is crucial for outstanding Li-ion conductors and may shed light on future design of high-performance solid electrolyte for solid state batteries

Femtosecond X-ray Laser Reveals Intact Sea-Island Structures of Metastable Solid-State Electrolytes for Batteries.

Experimental characterization of the nanostructure of metastable functional materials has attracted significant attention with recent advances in computational materials discovery. However, since metastable glass-ceramics are easily damaged by irradiation, damage-free nanoimaging has not been realized thus far. Herein, we propose novel high-contrast coherent diffractive imaging that quantitatively analyzes the intact internal nanostructure of metastable glass-ceramics using femtosecond X-ray pulses. The immersion of sample particles in a solvent helps enhance the reconstructed image contrast and allows us to distinguish an ∼7% electron density difference between an amorphous form and crystals. Furthermore, morphological operations with a band-pass filter quantitatively elucidate the depth information. The evaluated volume ratio of the amorphous to crystalline phases is ∼2.5:1 for the measured metastable (Li2S)70-(P2S5)30 glass-ceramic particle. Sulfide glass-ceramics are used as electrolytes for all-solid-state batteries, which are indispensable for reducing the carbon footprint. Our results will facilitate structural studies on fragile metastable materials with important scientific and industrial implications.

Revealing milling durations and sintering temperatures on conductivity and battery performances of Li2.25Zr0.75Fe0.25Cl6 electrolyte

Halide electrolytes in solid-state batteries with excellent oxidative stability and high ionic conductivity have been well reported recently. However, the high-cost rare-earth elements and long duration of high-rotation milling procure are the major obstacles. Herein, we have successfully synthesized the low cost Li2.25Zr0.75Fe0.25Cl6 electrolyte consisting of abundant elements with comparable Li-ion conductivity in a short milling duration of 4 h. Phase transition of the annealed sample was also carefully investigated. LiNi0.6Co0.2Mn0.2O2/Li2.25Zr0.75Fe0.25Cl6/Li5.5PS4.5Cl1.5/In-Li batteries using different halide electrolytes were constructed and cycled at different voltage windows. Solid-state battery using Li2.25Zr0.75Fe0.25Cl6 electrolyte obtained from long milling duration delivers higher discharge capacities and superior capacity retention than shorter milling time between 3.0 and 4.3 V. It delivers much higher discharge capacity when cycled at elevated temperature (60 °C) and suffers fast capacity degradation when the upper cut-off voltage increases to 4.5 V at the same current density. This work provides an efficiency synthesis strategy for halide solid electrolyte and studies its applications in all-solid-state batteries in a wide temperature range.

Lithium nitride coatings deposited by magnetron sputtering on sulfide electrolytes for solid-state batteries

Lithium nitride coatings deposited by magnetron sputtering on sulfide electrolytes for solid-state batteries

Rate-dependent deformation of amorphous sulfide glass electrolytes for solid-state batteries

Sulfide glasses are emerging as potential electrolytes for solid-state batteries. The mechanical behavior of these materials can significantly impact cell performance, and it is thus imperative to understand their deformation and fracture mechanisms. Previous work mainly reports properties obtained under quasi-static loading conditions, but very little is known about deformation under dynamic conditions. The current investigation shows that the sulfide glass mechanical behavior is dominated by viscoplasticity, differing substantially from polycrystalline oxide and sulfide solid electrolytes. Finite element modeling indicates that the sulfide glass stiffness is high enough to maintain good contact with softer lithium metal electrodes under moderate stack pressures. The observed viscoplasticity also implies that battery operating conditions will play an important role in electro-chemo-mechanical processes that are associated with dendritic lithium penetration. In general, the rate-dependent mechanical behavior of the sulfide glass electrolytes documented here offers a new dimension for designing next-generation all-solid-state batteries.

Structural and Mechanical characteristic study of HPMC polymer composite films

Hydroxypropyl methylcellulose (HPMC) were extensively known material in packaging, agriculture, medicine, electrolytes in solid state batteries and other areas due to the exceptional biocompatibility and easy production, however shows lower mechanical behaviour. The current investigation was embraced to delineate the effect of potassium iodide (KI) on structural and mechanical properties of biopolymer electrolyte films grounded on Hydroxypropyl methylcellulose (HPMC). The liquidation of the salt into the polymer crowd is done by solution cast technique and the X – Ray diffraction (XRD) analyses were used to fix the structural properties of pristine HPMC and composite HPMC films. The crystallinity (Xc) was calculated, the pristine HPMC films shows high level of crystallinity. However improved amorphous spaces of HPMC polymer crowd were exposed in HPMC composite films. The addition of KI had a considerable impact on break elongation. In HPMC, KI showed good intercalation, and large concentrations of KI resulted in crater-like pits on the film surfaces. Reductions in the tensile strength and elastic modulus along with an increase in elongation were noticed in film integrated with KI.

Biomimetic brain-like nanostructures for solid polymer electrolytes with fast ion transport

The intrinsic drawbacks of electrolytes and the growth of lithium dendrites limit the development of commercial lithium batteries. To address the aforementioned challenges, a novel biomimetic brain-like nanostructure (BBLN) solid polymer electrolyte was created by manipulating the shape of the incorporated nanoparticles. Our designed BBLN solid polymer electrolyte was created by incorporating spherical core-shell (UIO-66@67) fillers into polymer electrolyte, which is significantly different from traditional polymer-based composite electrolytes. UIO-66@67 spherical nanoparticles are highly favorable to eliminating polymer electrolyte stress and deformation during solidification, indicating a great potential for fabricating highly uniform BBLN solid polymer electrolytes with a substantial number of continuous convolutions. Furthermore, spherical nanoparticles can significantly reduce the crystalline structure of polymer electrolytes, improving polymer chain segmental movement and providing continuous pathways for rapid ion transfer. As a result, BBLN solid polymer electrolyte shows excellent ionic conductivity (9.2 × 10−4 S cm−1), a high lithium transference number (0.74), and outstanding cycle stability against lithium electrodes over 6500 h at room temperature. The concept of biomimetic brain-like nanostructures in this work demonstrates a novel strategy to enhance ion transport in polymer-based electrolytes for solid-state batteries.

Achieving superior ionic conductivity of Li6PS5I via introducing LiCl

Li6PS5I electrolyte shows significant potential as solid electrolytes due to its low cost and high stability. However, the poor room temperature Li-ion conductivity (10−6 S/cm) limits its applications in solid-state batteries. This work aims to increase the conductivity of Li6PS5I by introducing LiCl in the structure using high-rotation mechanical milling. Structure analysis confirms that a minor dopant of Cl− can form a single-phase of Li6PS5ClxI1-x argyrodite electrolytes, while a large doping amount yields a mixture of the Li6PS5I and Li6PS5Cl phases. The modified electrolytes with “composition” Li6PS5Cl0.7I0.3 show the highest room temperature Li-ion conductivity among the milled and sintered sample, 7.37 × 10−4 and 2.33 × 10−3 S/cm, both of which are much higher than the conductivity of pristine Li6PS5I. Solid-state batteries using the above solid electrolytes combined with LiNbO3-coated LiNi0.7Mn0.2Co0.1O2 cathode and LiIn anode display excellent electrochemical performances. The battery using annealed Li6PS5Cl0.7I0.3 electrolyte delivers improved discharge capacities and extended cycling performances at different operating temperatures. This work provides an effective strategy to design high conductivity Li6PS5I-based solid electrolytes for solid-state batteries.

Interfacial Barrier of Ion Transport in Poly(ethylene oxide)-Li7La3Zr2O12 Composite Electrolytes Illustrated by 6Li-Tracer Nuclear Magnetic Resonance Spectroscopy.

Fundamental understanding of the lithium-ion transport mechanism in polymer-inorganic composite electrolyte is crucially important for the rational design of composite electrolytes for solid-state batteries. In this work, the Li+ ion transport pathway in a model composite electrolyte of PEO containing sparsely dispersed LLZO (PEO-LLZO) was studied by an advanced characterization technique, i.e., 6Li-tracer NMR spectroscopy. By analyzing the 6Li distribution within the PEO-LLZO composite at the end of the discharge of an electrochemical cell of 6Li | PEO-LLZO | stainless steel with a fixed capacity (less than the total amount of the Li+ in the composite) at various current densities, it is found that the interfacial barrier between LLZO and PEO could cause a reduced Li+ flux through LLZO, particularly at high current densities, and therefore plays a critical role in determining the Li+ transport pathway in the composite electrolyte. This work provides an intuitive picture of Li+ ion transport in a polymer-inorganic composite electrolyte that is helpful to optimize and design better composite electrolytes.

The origin of high Na+ ion conductivity in Na1+xZr2SixP3-xO12 NASICON materials.

Due to the high sodium ion conductivity, sodium super ionic conductors (NASICONs) are among the most promising candidates as solid electrolytes in solid state batteries and have therefore gained enormous attention in recent years. Previous experimental and computational investigations show excellent sodium ion conductivity for Na1+xZr2SixP3-xO12 with x = 2-2.5. In order to elucidate the conductivity maximum at high substitution levels, we investigate the influence of the cation environment on the site energies of sodium ions and the correlated migration using density functional theory. The results reveal that the site energy strongly depends on electrostatic effects. In addition, an increasing fraction of sodium and silicon ions enhances the correlated migration due to the increasing coulombic repulsion of sodium ions and opening of the bottleneck along the migration path. Based on the results, we generate an energy model to predict configurational and migration energy in subsequent Kinetic Monte Carlo simulations. We show that sodium ions are trapped due to introduced silicon ions but percolate in the system for x≥2.0, which greatly increases the ionic conductivity.

Conductivity, microstructure and mechanical properties of tape-cast LATP with LiF and SiO2 additives

LATP sheets with LiF and SiO2 addition prepared by tape cast as electrolytes for solid-state batteries were characterized regarding conductivity, microstructure and mechanical properties aiming toward an optimized composition. The use of additives permitted a reduction of the sintering temperature. Rietveld analyses of the samples with additives revealed a phase mixture of NaSICON modifications crystallizing with rhombohedral and orthorhombic symmetry as a superstructure with space group Pbca. It seems that LiF acts as a sintering additive but also as a mineralizer for the superstructure of LATP. As general trend, higher LiF to SiO2 ratios led to lower porosities and higher values of elastic modulus and hardness determined by indentation testing, but the presence of the orthorhombic LATP leads to a decrease in the ionic conductivity. Micro-pillar testing was used to assess the crack growth behavior revealing weak grain boundaries.

Factors controlling the physical properties of an organic ionic plastic crystal

Organic ionic plastic crystals (OIPCs) containing organic cations and inorganic anions are gaining tremendous attention as an unconventional type of crystalline material. They usually possess one or more solid-solid phase transitions due to different levels of thermodynamic molecular motion, and also display diverse ionic conductivity and plasticity. Until today, we have not fully understood the main determinants of these properties, which are critical to designing the material to meet requirements for practical applications, such as solid-state battery electrolytes. In this work, we conducted a comprehensive experimental and computational investigation on a recently reported ammonium-based OIPC, which possesses only a single solid-solid phase transition before melting. This material maintains a very organized structure orderly at temperatures up to the melting point. The volume expansion along three sides of the crystal structure during heating is anisotropic, mainly on the a-side, controlled by different interionic forces between adjacent ions in each direction. The c-side of the crystal lattice experiences the strongest attraction, such as hydrogen bonding, reflected in the shortest CH⋅⋅⋅O distance of 2.293 Å, which is believed to hinder the rotation and translation of ions, thus decreases the plasticity of OIPC, and also results in the preservation of the long-range crystalline order. The single OIPC phase transition here is due to the growth in the rotational motions of the cations and anions. These observations are different from the previously reported phosphonium salt, suggesting that the interionic force and chemical structures significantly affect the physical, thermodynamic and phase behavior of OIPCs.

Development of Hybrid Electrolytes for Solid-State Batteries

Development of Hybrid Electrolytes for Solid-State Batteries