Battery Technology

Transformations at interfaces between solid-state electrolytes (SSEs) and lithium metal electrodes can lead to high impedance and capacity decay during cycling of solid-state batteries, but the links between structural/chemical/mechanical evolution of interfaces and electrochemistry are not well understood. Here, we use in situ X-ray computed tomography to reveal the evolution of mechanical damage within a Li 1+ x Al x Ge 2– x (PO 4 ) 3 (LAGP) SSE caused by interphase growth during electrochemical cycling. The growth of an interphase with expanded volume drives fracture in this material, and the extent of fracture during cycling is found to be the primary factor causing the impedance increase, as opposed to the resistance of the interphase itself. Cracks are observed to initiate near the edge of the lithium/LAGP interface, which agrees with simulations. The chemomechanical effects of interphase growth studied here are expected to play a role in a variety of SSE materials, and this work is a step toward designing durable interfaces.

Abstract 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 Na 1+x Zr 2 Si x P 3−x O 12 (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 Na 3.4 Zr 2 Si 2.4 P 0.6 O 12 , 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.

Epitaxial thin films of Al-doped Li7La3Zr2O12 (LLZO) with a cubic garnet-type structure were successfully synthesized using pulsed laser deposition to investigate the lithium ion conduction in grains. Two orientations of the films were obtained depending on the Gd3Ga5O12 (GGG) substrate orientation, LLZO(001)/GGG(001) and LLZO(111)/GGG(111). The ionic conductivities in the grains of the (001) and (111) films were 2.5 × 10(-6) and 1.0 × 10(-5) S cm(-1) at 298 K, respectively, which were lower than those of polycrystalline LLZO of over 10(-4) S cm(-1). X-ray reflectometry and inductively coupled plasma mass spectrometry revealed a large amount of Al(3+) of over 0.6 moles substituted for Li(+). These results indicate that the Al(3+) substitution in the LLZO lattice decreases the number of movable lithium ions and blocks the three-dimensional lithium migration pathway. The lattice mismatch between the film and the substrate induced the lattice distortion of the LLZO, resulting in different conductivities between the (001) and (111) films. The epitaxial-film model system directly clarified a substantial impact of the Al substitution and the lattice distortion on the lithium ion conductivity in the LLZO.

The search for safer next-generation lithium ion batteries has motivated development of solid-state electrolytes (SSEs), owing to their wide electrochemical potential window, high ionic conductivity (10−3 to 10−4 S cm−1) and good chemical stability with a wide range of high charge capacity electrode materials. Still, optimization of the processing conditions of SSEs without sacrificing the performance of the complete cell assembly remains challenging. Insights extracted from scientific literature can accelerate the optimization of processing protocols of SSEs, yet digesting the information scattered over thousands of journal articles is tedious and time consuming. In this work, we demonstrate the role of text mining to automatically compile materials synthesis parameters across tens of thousands of scholarly publications using machine learning and natural language processing techniques that glean information into the processing of sulfide and oxide-based Li SSEs. We also gain insight on low temperature synthesis of highly potential oxide-based Li garnet electrolytes, notably Li7La3Zr2O12 (LLZO), which can reduce the interface complexities during integration of the SSE into cell assembly. This work demonstrates the use of text and data mining to expedite the development of all-solid-state Li metal batteries by guiding hypotheses during experimental design.

Monolithic heterojunction quasi-solid-state battery electrolytes (MH-QEs) based on thermodynamically immiscible dual phases are presented as an electrode-customized multifunctional electrolyte.

All-solid-state batteries are promising energy storage devices owing to their high safety and energy density. Sulfide-based solid electrolytes have high ionic conductivities and are ductile. Although sulfide electrolytes are candidates for all-solid-state batteries, they are moisture-sensitive. Li 4 SnS 4 electrolytes can overcome some of these weaknesses and show the suppressed evolution of H 2 S gas in a humid environment. However, the suppression mechanism is unclear, making the design of moisture-resistant sulfide electrolytes challenging. Therefore, we investigated the structural changes of Li 4 SnS 4 in humid N 2 . X-ray structural analysis revealed that Li 4 SnS 4 was hydrated to Li 4 SnS 4 ·4H 2 O without generating H 2 S gas. Furthermore, the hydrate could be reversibly dehydrated by heat treatment to the original sulfide, suggesting that the formation of stable hydrates suppresses the generation of H 2 S gas. These findings will aid in the design of moisture-resistant sulfide materials.

Sulfide solid electrolytes (SEs) exhibit excellent ionic conductivity and good mechanical properties, but their poor air stability and solid-solid contact performance seriously hinder the wide application of sulfide all-solid-state batteries (ASSBs). Herein, this paper reviews the history and the major breakthroughs in the development of sulfide SEs. The theories of hard-soft-acid-base theory and glass structure theory, as well as several strategies to improve the chemical stability of sulfide SEs, are discussed emphatically. In addition, this paper also explores its thermal runaway mechanism and reaction mechanism from the aspects of thermodynamics and reaction kinetics, providing a reference for the research on improving stability and electrical conductivity. Finally, we summarized the challenges that still need to be addressed at present, as well as the research directions and prospects of sulfide SEs for ASSBs in the future.

With a growing interest on inorganic ceramics based solid-state electrolytes for all-solid-state batteries, there is a need to maximise their density to optimise electrochemical performance and fuel impermeability. In this paper, we demonstrate the sensitivity of terahertz time-domain spectroscopy (THz-TDS) combined with effective medium theory to quantify the porosity or density of sodium superionic conductor (NaSICON)-based solid-state electrolyte (SSEs) pellets prepared at densities in the range of 2.2–2.9 g cm−3, corresponding to 50–90 % relative densities sintered at 900–1150 °C. The results of which, have been validated against complementary Archimedes analysis and mercury porosimetry highlighting the potential of THz-TDS for rapid, contactless, non-destructive electrolyte characterisation.

Defective regions in battery materials often generate excess or non-uniform heat profiles during operation. Here, we discuss lock-in thermography as a high-sensitivity, spatially-resolved, and non-destructive technique to characterize defects and guide the targeted optimization of new battery materials and cell designs. As an example, we thermally image all-solid-state cells with β-Li 3 PS 4 electrolyte, showing point-like heat signatures that correlate with cell breakdown. Based on the current/voltage cycling characteristics and electrochemical impedance spectroscopy, we attribute heating at the breakdown sites primarily to resistive current flow through dendrites. To assist in enabling wider application of lock-in thermography to emerging battery materials, we discuss several parameters necessary to optimize this technique, including the influences of surface thermal emissivity, thermal diffusivity, and lock-in modulation frequency.

Borate glasses are gaining attention as solid-state electrolytes for next-generation lithium batteries because of their distinctive structural and electrochemical characteristics. Their amorphous framework enables the formation of continuous lithium ion pathways, resulting in high ionic conductivity and enhanced transport kinetics. Borate glasses also offer a broad electrochemical stability window, which makes them well suited for high voltage applications and enhances safety compared to traditional liquid electrolytes. Recent studies highlight their versatility, as they can function both as bulk electrolytes and as protective interfacial coatings that mitigate electrode degradation and suppress dendrite growth. This review consolidates current progress in the design, synthesis, and characterization of borate glass electrolytes, with emphasis on their ion conduction mechanisms, structural features, and electrochemical performance. Challenges such as optimizing mechanical stability, scalability, and compatibility with diverse electrode chemistries are critically discussed. Finally, future perspectives are outlined to guide the development of borate glass based solid-state batteries toward practical, high energy density applications.

Solid electrolytes in all solid-state batteries, provide higher attainable energy density and improved safety. Ideal solid electrolytes require high ionic conductivity, a high elastic modulus to prevent dendrite growth, chemical compatibility with electrodes, and ease of fabrication into thin films. Although various materials types, including polymers, ceramics, and composites, are under intense investigation, unifying design principles have not been identified. In this thesis, we study the key ion transport mechanisms in relation to the structural characteristics of polymers and glassy solids, and apply derived material design strategies to develop polymer-silica hybrid materials with improved electrolyte performance characteristics. Poly(ethylene) oxide-based solid electrolytes containing ceramic nanoparticles are attractive alternatives to liquid electrolytes for high-energy density Li batteries. We compare the effect of Li1.3Al0.3Ti1.7(PO4)3 active nanoparticles, passive TiO2 nanoparticles and fumed silica. Up to two orders of magnitude enhancement in ionic conductivity is observed for composites with active nanoparticles, attributed to cation migration through a percolating interphase region that develops around the active nanoparticles, even at low nanoparticle loading. We investigate the structural origin of elastic properties and ionic migration mechanisms in sodium borosilicate and sodium borogermanate glass electrolyte system. A new statistical thermodynamic reaction equilibrium model is used in combination with data from nuclear magnetic resonance and Brillouin light scattering measurements to determine network structural unit fractions. The highly coordinated structural units are found to be predominantly responsible for effective mechanical load transmission, by establishing three-dimensional covalent connectivity. A strong correlation exists between bulk modulus and the activation energy for ion conduction. We describe the activated process in glasses as involving a jump by the migrating cation and transient reversible isotropic displacement of atoms in the immediate vicinity, and express the activation energy as a sum of Coulomb and elastic terms. By fitting our experimental data to this model, we find that the number of affected atoms in the vicinity ranges between 20 and 30. Furthermore, elastic deformations in ion jumping are almost purely hydrostatic and hardly shear. Considering that the energy required for the cation jump is made available by concentrating thermal phonons at the jump site, we establish a relationship between structural stiffness and activation energy. Moreover, the more atoms that partake in the cation jump, the more degrees of freedom for atomic motion can be relied upon to achieve the required net outward expansion to facilitate the passage of the jumping cation, lowering the activation energy. To combine the flexibility of polymers and the good mechanical and electrochemical properties of silica, we use sol-gel methods for fabricating silica-based hybrid organic-inorganic electrolytes. Polyethylene glycol is covalently grafted onto the silica backbone as the organic filler that provides the environment for ion conduction. We developed synthesis methods in which grafting and polycondensation occur concurrently, or the grafting occurs after the silica backbone has formed. Small angle x-ray scattering measurements reveal that different structures are achieved depending on the method used. The two-step procedure allows for a larger amount of conducting polymer to be embedded into network pores than in the one-pot method. This greatly enhances the ionic conductivity without sacrificing mechanical stability afforded by the continuous silica backbone. Here we provide a cumulative account of a systematic materials design efforts, in which we sequentially implement several important design aspects to identify their respective importance and influence on the materials performance characteristics.