Thermo-Mechanical Stress Analysis and Critical Condition Estimation in Lithium Lanthanum Niobate (LiLaNbO) Thin Electrolyte Plate of All-Solid-State Battery

Araki W., Choudhury T.T., Arai Y.

• Thermo-chemo-mechanical stress field in an electrolyte was successfully formulated. • Stress was calculated using property variations with temperature and Li concentration. • Critical conditions for safe operation was estimated to limit maximum induced stress. • Suggested method could be developed further for various practical applications. Stress fields of the electrolytes of all-solid-state batteries can be induced by several factors, such as temperature variations, lithium-ion distributions, and mechanical constraints. In this study, the thermo-chemo-mechanical stress field in an electrolyte was formulated using plate theory, assuming an infinite thin-electrolyte plate in a planar battery system. The stress fields were successfully calculated with consideration of property variations with temperature and lithium concentration under various conditions of temperature gradients, lithium concentration profiles, and mechanical boundary constraints. The extent to which the property variations affected the stress fields was also demonstrated. From these calculated stress distributions, an estimation method of the critical conditions for safe operation was proposed to limit maximum stress induced in electrolytes.

Choudhury T.T., Araki W., Yamada N., Arai Y.

• Mechanical behaviours of Li 3 x La 1/3− x NbO 3 (3 x = 0.00–0.18) with domain structures. • Orthorhombic LLNbO reveals non-linear elastic hysteresis due to domain reorientations. • Tetragonal LLNbO reveals simple elastic behaviour with almost no domain change. This study investigates the mechanical behaviours of A-site deficient perovskite-type Li 3 x La 1/3− x NbO 3 electrolytes (3 x = 0.00–0.18) with domain structures. The samples were examined under uniaxial compression in the temperature range of 233–393 K. In the stress vs. strain relationship, the orthorhombic Li 3 x La 1/3− x NbO 3 (3 x ≤ 0.06) clearly exhibits non-linear elastic hysteresis, whilst the tetragonal one (3 x ≥ 0.12) shows a simple elastic behaviour. Ex-situ scanning electron microscopy observation on a polished surface before and after compression confirmed the martensitic reorientation of the domain structure of the orthorhombic Li 3 x La 1/3− x NbO 3 , which explains the observed non-linear hysteresis, whereas the domains of the tetragonal sample remain almost unchanged.

Wu Y., Wang S., Li H., Chen L., Wu F.

Thermal safety is one of the major issues for lithium-ion batteries (LIBs) used in electric vehicles. The thermal runaway mechanism and process of LIBs have been extensively studied, but the thermal problems of LIBs remain intractable due to the flammability, volatility and corrosiveness of organic liquid electrolytes. To ultimately solve the thermal problem, all-solid-state LIBs (ASSLIBs) are considered to be the most promising technology. However, research on the thermal stability of solid-state electrolytes (SEs) is still in its initial stage, and the thermal safety of ASSLIBs still needs further validation. Moreover, the specified reviews summarizing the thermal stability of ASSLIBs and all types of SEs are still missing. To fill this gap, this review systematically discussed recent progress in the field of thermal properties investigation for ASSLIBs, form levels of materials and interface to the whole battery. The thermal properties of three major types of SEs, including polymer, oxide, and sulfide SEs are systematically reviewed here. This review aims to provide a comprehensive understanding of the thermal stability of SEs for the benign development of ASSLIBs and their promising application under practical operating conditions.

Park G., Kim H., Oh J., Choi Y., Ovchinnikova O.S., Min S., Lee Y., Hong S.

Here, we present a quantitative method to measure the concentration and diffusivity of Li ion in a solid-state electrolyte with nanoscale depth resolution. We designed a standard sample with differ...

Lu J., Li Y., Ding Y.

Perovskite-type Li3x-yLa1-xAl1-yTiyO3 (x = 5y/12) solid electrolytes with varying Ti content (y = 0.4, 0.6, 0.8, 0.9, and 1) were prepared by conventional solid-state reaction process. Furthermore, the crystal structure, Li-ion conductivity, and electrochemical stability were investigated by X-ray diffraction, alternating current impedance, and cyclic voltammetry. X-ray diffraction analysis showed minimum impurities and a change from cubic to tetragonal with increasing Ti content. Maximum bulk and total conductivities of 1.99 × 10–3 S cm–1 and 4.53 × 10–4 S cm–1 were obtained in Li0.25La0.583TiO3, with activation energy of 0.28 eV and electronic conductivity of 2.30 × 10–9 S cm–1 at 20 °C. Cyclic voltammetry showed that Al-contained materials such as Li0.2La0.667Al0.2Ti0.8O3, and Li0.225La0.625Al0.1Ti0.9O3 were slightly more stable than Li0.25La0.583TiO3 vs. Li+/ Li. LiFePO4/Li batteries were fabricated using Li0.225La0.625Al0.1Ti0.9O3, and Li0.25La0.583TiO3 as solid electrolyte separators, a capacity of 79.0, and 112.0 mA h g–1 at 25 °C were maintained over 100 cycles, respectively.

Bistri D., Afshar A., Di Leo C.V.

Solid-state-batteries (SSBs) present a promising technology for next-generation batteries due to their superior properties including increased energy density, wider electrochemical window and safer electrolyte design. Commercialization of SSBs, however, will depend on the resolution of a number of critical chemical and mechanical stability issues. The resolution of these issues will in turn depend heavily on our ability to accurately model these systems such that appropriate material selection, microstructure design, and operational parameters may be determined. In this article we review the current state-of-the art modeling tools with a focus on chemo-mechanics. Some of the key chemo-mechanical problems in SSBs involve dendrite growth through the solid-state electrolyte (SSE), interphase formation at the anode/SSE interface, and damage/decohesion of the various phases in the solid-state composite cathode. These mechanical processes in turn lead to capacity fade, impedance increase, and short-circuit of the battery, ultimately compromising safety and reliability. The article is divided into the three natural components of an all-solid-state architecture. First, modeling efforts pertaining to Li-metal anodes and dendrite initiation and growth mechanisms are reviewed, making the transition from traditional liquid electrolyte anodes to next generation all-solid-state anodes. Second, chemo-mechanics modeling of the SSE is reviewed with a particular focus on the formation of a thermodynamically unstable interphase layer at the anode/SSE interface. Finally, we conclude with a review of chemo-mechanics modeling efforts for solid-state composite cathodes. For each of these critical areas in a SSB we conclude by highlighting the key open areas for future research as it pertains to modeling the chemo-mechanical behavior of these systems.

Araki W., Nagakura Y., Arai Y.

The present study investigated thermo-mechanical behaviour of A-site deficient perovskites Li3xLa1/3-xTaO3 (LLTaO) and Li3xLa1/3-xNbO3 (LLNbO) with x = 0.00 to 0.06 as a function of temperature by means of thermo-mechanical analysis. LLTaO for all compositions exhibits an orthorhombic-tetragonal phase transition around 200 K, above which it has a tetragonal phase. As the temperature increases from 200 K to 400 K, the linear expansion coefficient shows a slight decrease for all the compositions, followed by a constant value of ~3 × 10−6 K−1 above 400 K regardless of x. On the other hand, LLNbO has an orthorhombic phase for x ≤ 0.02 and the tetragonal for x ≥ 0.04 at room temperature. The linear expansion coefficient of LLNbO with x ≤ 0.02 shows a peak around 470 K, which can be attributed to an orthorhombic-tetragonal phase transition. In addition, the expansion coefficient of LLNbO with x ≥ 0.02 significantly increases as the temperature rises from 200 K to 400 K, followed by a plateau and a relatively abrupt decrease after reaching a temperature above 600 K. Additional ionic conductivity measurement of LLNbO suggested that the inconstant expansion behaviour could be attributed to the lithium-ion motion.

Tsukasaki H., Otoyama M., Mori Y., Mori S., Morimoto H., Hayashi A., Tatsumisago M.

Sulfide-based all-solid-state batteries using a non-flammable inorganic solid electrolyte are promising candidates as a next-generation power source owing to their safety and excellent charge–discharge cycle characteristics. In this study, we thus focus on the positive electrode and investigated structural stabilities of the interface between the positive electrode active material LiNi 1/3 Mn 1/3 Co 1/3 O 2 (NMC) and the 75Li 2 S·25P 2 S 5 (LPS) glass electrolyte after charge–discharge cycles via transmission electron microscopy (TEM). To evaluate the thermal stability of the fabricated all-solid-state cell, in-situ TEM observations for the positive electrode during heating are conducted. As a result, structural and morphological changes are detected in the LPS glasses. Thus, exothermal reaction present in the NMC-LPS composite positive electrode after the initial charging is attributable to the crystallization of LPS glasses. On the basis of a comparison with crystallization behavior in single LPS glasses, the origin of exothermal reaction in the NMC-LPS composites is discussed.

Bucci G., Swamy T., Chiang Y., Carter W.C.

This is the first quantitative analysis of mechanical reliability of all-solid state batteries. Mechanical degradation of the solid electrolyte (SE) is caused by intercalation-induced expansion of the electrode particles, within the constrains of a dense microstructure. A coupled electro-chemo-mechanical model was implemented to quantify the material properties that cause an SE to fracture. The treatment of microstructural details is essential to the understanding of stress-localization phenomena and fracture. A cohesive zone model is employed to simulate the evolution of damage. In the numerical tests, fracture is prevented when electrode-particle's expansion is lower than 7.5% (typical for most Li-intercalating compounds) and the solid-electrolyte's fracture energy higher than Gc = 4 J m−2. Perhaps counter-intuitively, the analyses show that compliant solid electrolytes (with Young's modulus in the order of ESE = 15 GPa) are more prone to micro-cracking. This result, captured by our non-linear kinematics model, contradicts the speculation that sulfide SEs are more suitable for the design of bulk-type batteries than oxide SEs. Mechanical degradation is linked to the battery power-density. Fracture in solid Li-ion conductors represents a barrier for Li transport, and accelerates the decay of rate performance.

Zhang L.C., Yang J.F., Gao Y.X., Wang X.P., Fang Q.F., Chen C.H.

The cubic Ca/Ta-substituted Li6.55(La2.95Ca0.05)(Zr1.5Ta0.5)O12 (LLCZTO) electrolytes were synthesized at 800 °C with Li3BO3 as additives. The optimal amount of Li3BO3 and its influences on the microstructure, crystal structures, Li+ conductivity and the stability of the Li6.55(La2.95Ca0.05)(Zr1.5Ta0.5)O12 were studied by SEM, XRD and EIS. Among all the samples, when the molar ratio of Li3BO3 to the Li6.55(La2.95Ca0.05)(Zr1.5Ta0.5)O12 is 4:5, the highest Li+ conductivity of 1.33 × 10−4 S cm−1 at 30 °C is obtained. When the LLCZTO samples are exposed in air, the Li+ conductivity is deteriorated possibly owing to the side reactions between the LLCZTO and the H2O or CO2 in the air. The Li3BO3 addition can alleviate such deterioration of the Li+ conductivity.

Kerman K., Luntz A., Viswanathan V., Chiang Y., Chen Z.

Solid state electrolyte systems boasting Li+ conductivity of >10 mS cm−1 at room temperature have opened the potential for developing a solid state battery with power and energy densities that are competitive with conventional liquid electrolyte systems. The primary focus of this review is twofold. First, differences in Li penetration resistance in solid state systems are discussed, and kinetic limitations of the solid state interface are highlighted. Second, technological challenges associated with processing such systems in relevant form factors are elucidated, and architectures needed for cell level devices in the context of product development are reviewed. Specific research vectors that provide high value to advancing solid state batteries are outlined and discussed.

Wu J., Chen L., Song T., Zou Z., Gao J., Zhang W., Shi S.

Due to various and indefinite Li-ion distributions within the cuboctahedron surrounded by eight TiO6 and local subtle distortions, perovskite-type solid electrolyte Li[Formula: see text]La[Formula: see text]TiO3 (LLTO) is suitable to be used as a model system for studying the structure–conductivity relationship. This review is focused on structural characteristics, Li-ion diffusion behavior and conductivity in LLTO. Li-ion concentration, cooling rate of heat treatment and heating temperature are shown to be three main factors influencing the space group structure of LLTO, involving the distributions of Li, La ions and vacancies as well as the distortion of TiO6 octahedron. In rhombohedral and some orthorhombic phases, Li ions partially occupy O4 windows of cuboctahedrons, whose diffusion could be described by the bond percolation model, whereas in other phases with Li ions inside the cuboctahedrons, the site percolation model is applicable to Li-ion conduction. Li-ion conductivity versus temperature curve exhibits non-Arrhenius behavior, which is divided into three sections with different activation energies, although its first-derivative is continuous. The activation energy is correlated closely with the tilting angle of TiO6 octahedron, both of which decrease with the increase of temperature. Experimental studies and theoretical results are discussed in parallel to provide insight into the detailed structure-conductivity relationship.

Fu K.(., Gong Y., Hitz G.T., McOwen D.W., Li Y., Xu S., Wen Y., Zhang L., Wang C., Pastel G., Dai J., Liu B., Xie H., Yao Y., Wachsman E.D., et. al.

A solid electrolyte framework with porous and dense layers for high-energy and safe Li-metal batteries.

Luo W., Gong Y., Zhu Y., Li Y., Yao Y., Zhang Y., Fu K.(., Pastel G., Lin C., Mo Y., Wachsman E.D., Hu L.

Substantial efforts are underway to develop all-solid-state Li batteries (SSLiBs) toward high safety, high power density, and high energy density. Garnet-structured solid-state electrolyte exhibits great promise for SSLiBs owing to its high Li-ion conductivity, wide potential window, and sufficient thermal/chemical stability. A major challenge of garnet is that the contact between the garnet and the Li-metal anodes is poor due to the rigidity of the garnet, which leads to limited active sites and large interfacial resistance. This study proposes a new methodology for reducing the garnet/Li-metal interfacial resistance by depositing a thin germanium (Ge) (20 nm) layer on garnet. By applying this approach, the garnet/Li-metal interfacial resistance decreases from ≈900 to ≈115 Ω cm2 due to an alloying reaction between the Li metal and the Ge. In agreement with experiments, first-principles calculation confirms the good stability and improved wetting at the interface between the lithiated Ge layer and garnet. In this way, this unique Ge modification technique enables a stable cycling performance of a full cell of lithium metal, garnet electrolyte, and LiFePO4 cathode at room temperature.

Sosunov A.V., Volyntsev A.B., Tsiberkin K.B., Yuriev V.A., Ponomarev R.S.

This paper reviews the features of the structure, composition and mechanical properties of the subsurface layer of pure lithium niobate. Depth of this layer ranges up to 20 μm, and it's structure a...