The development of new materials leads to the invention of new devices. The exploitation of high ionic conductivity materials has facilitated the emergence of a new category of energy storage ...devices, including the all-solid-state battery. This paper reviews the history of the development of lithium solid electrolytes and their application in all-solid-state batteries. Particular focus is given to the development process of Li10GeP2S12, which surpasses the conductivity characteristics of liquid-electrolyte systems targeted by lithium-ion conductors, and its application to solid-state batteries is described. Furthermore, this review describes new science that will be born when batteries become solid-state.
Ever since the first report on Li10GeP2S12 (LGPS) in 2011, its unique structure and exceptionally high lithium conductivity (>1 × 10−2 S cm−1) have attracted extensive interest, especially for ...applications in solid‐state ionics and batteries. Herein, studies of LGPS and its modifications are reviewed with a focus on the synthesis, structure, and ionic transportation of LGPS. For material synthesis, the relationships between LGPS and its precursor compounds such as Li3PS4 and Li4GeS4 are discussed. A technique for single‐crystal growth and a family of LGPS‐type materials that are chemically or structurally related to LGPS are then described. The crystal structure of LGPS is analyzed from the viewpoints of tetrahedral framework units, anion sublattice, and Li distributions; furthermore, the conduction mechanism is qualitatively analyzed. Subsequently, ionic transportation in LGPS is studied quantitatively. The origin of the high conductivity is discussed in terms of the activation energy, diffusion coefficient, and its related parameters; and these factors are compared to those of other non‐LGPS‐type conductors. Then, the battery applications are briefly summarized to indicate the potential merits of using LGPS‐type solid electrolytes with high lithium conductivity. Any remaining issues and possible research directions that have emerged from the aforementioned studies are finally highlighted.
Studies on superionic lithium conductors (Li10GeP2S12) are reviewed herein, focusing on their synthesis, structure, and ionic transportation. This review begins with phase‐diagram and single‐crystal studies, and subsequently summarizes the chemical or structural derivatives. After Li distribution in the unique crystal structure is overviewed, the ion conduction mechanism is discussed to obtain insights for developing new conductors.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
This issue contains assessments of battery performance involving complex, interrelated physical and chemical processes between electrode materials and electrolytes. Transformational changes in ...battery technologies are critically needed to enable the effective use of renewable energy sources such as solar and wind to allow for the expansion of hybrid electric vehicles (HEVs) to plug-in HEVs and pure-electric vehicles. For these applications, batteries must store more energy per unit volume and weight, and they must be capable of undergoing many thousands of charge-discharge cycles. The articles in this theme issue present details of several growing interest areas, including high-energy cathode and anode materials for rechargeable Li-ion batteries and challenges of Li metal as an anode material for Li batteries. They also address the recent progress in systems beyond Li ion, including Li-S and Li-air batteries, which represent possible next-generation batteries for electrical vehicles. One article reviews the recent understanding and new strategies and materials for rechargeable Mg batteries. The knowledge presented in these articles is anticipated to catalyze the design of new multifunctional materials that can be tailored to provide the optimal performance required for future electrical energy storage applications.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Abstract
All-solid-state batteries are intensively investigated, although their performance is not yet satisfactory for large-scale applications. In this context, the combination of Li
10
GeP
2
S
12
...solid electrolyte and LiNi
1-x-y
Co
x
Mn
y
O
2
positive electrode active materials is considered promising despite the yet unsatisfactory battery performance induced by the thermodynamically unstable electrode|electrolyte interface. Here, we report electrochemical and spectrometric studies to monitor the interface evolution during cycling and understand the reactivity and degradation kinetics. We found that the Wagner-type model for diffusion-controlled reactions describes the degradation kinetics very well, suggesting that electronic transport limits the growth of the degradation layer formed at the electrode|electrolyte interface. Furthermore, we demonstrate that the rate of interfacial degradation increases with the state of charge and the presence of two oxidation mechanisms at medium (3.7 V
vs
. Li
+
/Li <
E
< 4.2 V
vs
. Li
+
/Li) and high (
E
≥ 4.2 V
vs
. Li
+
/Li) potentials. A high state of charge (>80%) triggers the structural instability and oxygen release at the positive electrode and leads to more severe degradation.
Reactions at the electrode/electrolyte interface of all-solid-state lithium batteries were studied for combinations of sulfide-based solid electrolytes with various Li4-xGe1-xPxS4 and Liy-M (M=Sn, ...Si) alloys as the negative electrodes, using ac impedance, X-ray diffraction and energy-dispersive X-ray spectroscopy. The solid electrolyte at the interfacial region was found to decompose with the application of a current through the cells, resulting in the formation of a solid electrolyte interphase (SEI) layer. Resistivity changes at the interface varied depending on the electrolyte composition and the redox potential (vs. Li/Li+) of the negative electrode material. Lower resistances were observed with lower Ge contents in the solid electrolyte and the use of a Li–M alloy with a higher redox potential due to the formation of an electrochemically stable SEI layer during battery operation. In contrast, a combination of higher Ge content and an alloy with a lower redox potential led to a rapid increase in the SEI resistance and increase in its thickness. The presence of a Li–P–S compound with low ionic conductivity in the interfacial region was found to be related with the increase of interfacial resistance, leading to poor cycling characteristics. The formation of a suitable SEI layer is an important factor in the future development of all-solid-state batteries and this study serves to clarify the relationships between the formation of the SEI phase, the redox potential of the electrode and the sulfide-based solid electrolyte composition.
•Interfacial resistances in all-solid-state lithium batteries were investigated.•AC impedance method clarified the changes of the resistance during battery operation.•Sulfide solid electrolytes were decomposed at lower voltage region (vs. Li/Li+).•Lower resistances were observed with lower Ge proportion in the Li4-xGe1-xPxS4.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
No design rules have yet been established for producing solid electrolytes with a lithium-ion conductivity high enough to replace liquid electrolytes and expand the performance and battery ...configuration limits of current lithium ion batteries. Taking advantage of the properties of high-entropy materials, we have designed a highly ion-conductive solid electrolyte by increasing the compositional complexity of a known lithium superionic conductor to eliminate ion migration barriers while maintaining the structural framework for superionic conduction. The synthesized phase with a compositional complexity showed an improved ion conductivity. We showed that the highly conductive solid electrolyte enables charge and discharge of a thick lithium-ion battery cathode at room temperature and thus has potential to change conventional battery configurations.
Single crystals of the lithium-ion conductor Li10GeP2S12 have been successfully grown by the self-flux method and are studied by means of X-ray diffraction and impedance spectroscopy. The weak ...anisotropic ionic conductivity is observed to be 27 and 7 mS cm–1 in the 001 and 110 directions, respectively, at room temperature. Markedly, however, the activation energies are nearly equal, approximately 0.3 eV, in the two directions, which means that common diffusion paths along 110 dominate the long-range diffusion in Li10GeP2S12.
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IJS, KILJ, NUK, PNG, UL, UM
Spinel-structured lithium manganese oxide (LiMn2O4) cathodes have been successfully commercialized for various lithium battery applications and are among the strongest candidates for emerging ...large-scale applications. Despite its various advantages including high power capability, however, LiMn2O4 chronically suffers from limited cycle life, originating from well-known Mn dissolution. An ironical feature with the Mn dissolution is that the surface orientations supporting Li diffusion and thus the power performance are especially vulnerable to the Mn dissolution, making both high power and long lifetime very difficult to achieve simultaneously. In this investigation, we address this contradictory issue of LiMn2O4 by developing a truncated octahedral structure in which most surfaces are aligned to the crystalline orientations with minimal Mn dissolution, while a small portion of the structure is truncated along the orientations to support Li diffusion and thus facilitate high discharge rate capabilities. When compared to control structures with much smaller dimensions, the truncated octahedral structure as large as 500 nm exhibits better performance in both discharge rate performance and cycle life, thus resolving the previously conflicting aspects of LiMn2O4.
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IJS, KILJ, NUK, PNG, UL, UM
Lithium ion conductivity in many structural families can be tuned by many orders of magnitude, with some rivaling that of liquid electrolytes at room temperature. Unfortunately, fast lithium ...conductors exhibit poor stability against lithium battery electrodes. In this article, we report a fundamentally new approach to alter ion mobility and stability against oxidation of lithium ion conductors using lattice dynamics. By combining inelastic neutron scattering measurements with density functional theory, fast lithium conductors were shown to have low lithium vibration frequency or low center of lithium phonon density of states. On the other hand, lowering anion phonon densities of states reduces the stability against electrochemical oxidation. Olivines with low lithium band centers but high anion band centers are promising lithium ion conductors with high ion conductivity and stability. Such findings highlight new strategies in controlling lattice dynamics to discover new lithium ion conductors with enhanced conductivity and stability.
Perovskite-type lithium ionic conductors were explored in the (LixLa1−x/3)ScO3 system following their syntheses via a high-pressure solid-state reaction. Phase identification indicated that a solid ...solution with a perovskite-type structure was formed in the range 0 ≤ x < 0.6. When x = 0.45, (Li0.45La0.85)ScO3 exhibited the highest ionic conductivity and a low activation energy. Increasing the loading of lithium as an ionic diffusion carrier expanded the unit cell volume and contributed to the higher ionic conductivity and lower activation energy. Cations with higher oxidation numbers were introduced into the A/B sites to improve the ionic conductivity. Ce4+ and Zr4+ or Nb5+ dopants partially substituted the A-site (La/Li) and B-site Sc, respectively. Although B-site doping produced a lower ionic conductivity, A-site Ce4+ doping improved the conductive properties. A perovskite-type single phase was obtained for (Li0.45La0.78Ce0.05)ScO3 upon Ce4+ doping, providing a higher ionic conductivity than (Li0.45La0.85)ScO3. Compositional analysis and crystal-structure refinement of (Li0.45La0.85)ScO3 and (Li0.45La0.78Ce0.05)ScO3 revealed increased lithium contents and expansion of the unit cell upon Ce4+ co-doping. The highest ionic conductivity of 1.1 × 10−3 S cm−1 at 623 K was confirmed for (Li0.4Ce0.15La0.67)ScO3, which is more than one order of magnitude higher than that of the (LixLa1−x/3)ScO3 system.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
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