RESUMEN
The practical utilization of all-solid-state sodium batteries necessitates the development of a mass synthesis process for high-alkali-content sulfide glass electrolytes, which are characterized by both high ionic conductivity and remarkable formability. Typically, vacuum sealing and quenching are conventional techniques employed during the manufacturing process. In this paper, we present a novel approach, a pioneering method for the production of sulfide glass electrolytes with high alkali concentrations, achieved through ambient-pressure heat treatment and a gradual cooling process. We enhance the glass-forming ability of Na3BS3 by incorporating a small quantity of SiO2. The ionic conductivity of the resulting Na3BS3·0.225SiO2 (molar ratio) glass exhibited 1.5 × 10-5 S cm-1 at 25 °C, surpassing that of Na3BS3 glass. An all-solid-state cell utilizing Na3BS3·0.225SiO2 glass is successfully operated as a secondary battery at 60 °C. Our findings suggest that sodium oxythioborosilicate glass with electrochemical properties identical to those of Na3BS3 can be prepared without the need for quenching. These results propel the advancement of research in the domain of mass production processes tailored for high-alkali-content sulfide glass.
RESUMEN
High-temperature metastable phases exhibit superior characteristics compared to those of thermodynamically stable phases at room temperature. Although optimization of the compositions and crystallizations from glasses contribute to the stabilization of metastable phases at room temperature, the stabilization of the high-temperature α-Li3PS4 phase is not yet reported. α-Li3PS4 was successfully stabilized at room temperature, instead of the middle-temperature ß-Li3PS4 phase, via rapid heating to crystallize the Li3PS4 glass. The obtained electrolyte exhibited a high ionic conductivity of >10-3 S cm-1 at room temperature. The crystallization of the glass via rapid heating overcame the thermodynamic limitations in the preparation of the metastable crystals. Further development of materials via nonequilibrium states should contribute to the design of high-performance materials.
RESUMEN
All-solid-state lithium-sulfur (Li/S) batteries are promising next-generation energy-storage devices owing to their high capacities and long cycle lives. The Li2 S active material used in the positive electrode has a high theoretical capacity; consequently, nanocomposites composed of Li2 S, solid electrolytes, and conductive carbon can be used to fabricate high-energy-density batteries. Moreover, the active material should be constructed with both micro- and nanoscale ion-conduction pathways to ensure high power. Herein, a Li2 S-Li2 O-LiI positive electrode is developed in which the active material is dispersed in an amorphous matrix. Li2 S-Li2 O-LiI exhibits high charge-discharge capacities and a high specific capacity of 998 mAh g-1 at a 2 C rate and 25 °C. X-ray photoelectron spectroscopy, X-ray diffractometry, and transmission electron microscopy observation suggest that Li2 O-LiI provides nanoscale ion-conduction pathways during cycling that activate Li2 S and deliver large capacities; it also exhibits an appropriate onset oxidation voltage for high capacity. Furthermore, a cell with a high areal capacity of 10.6 mAh cm-2 is demonstrated to successfully operate at 25 °C using a Li2 S-Li2 O-LiI positive electrode. This study represents a major step toward the commercialization of all-solid-state Li/S batteries.
RESUMEN
The new binary sodium magnesium sulfide was prepared by the mechanochemical synthesis route from Na2S and MgS as starting materials. Na6MgS4 is extremely sensitive and partially decomposes in the presence of oxygen traces. With the use of an excess of MgS in the milling process, the molar ratio of the impurities was successfully decreased from 38% (Na2S + MgO) to 13% MgO. The crystal structure and properties were characterized by X-ray powder diffraction, thermogravimetry/differential thermal analysis, scanning electron microscopy-energy-dispersive X-ray spectroscopy, and electrochemical impedance spectroscopy. The Rietveld refinement confirmed that Na6MgS4 is isostructural to Na6ZnO4. The compound crystallized in the hexagonal system in the non-centro-symmetric space group P63mc (No. 186) with a = 9.0265(1), c = 6.9524(1) Å, V = 490.58(1) Å3, and Z = 2. The structure consisted of a wurtzite-like 3D framework built up of corner-sharing MgS4 and NaS4 tetrahedra, with 3/4 of the tunnels, parallel to the c axis, filled with octahedrally coordinated sodium atoms. The ionic conductivity of the composite material (87% Na6MgS4 + 13% MgO) being low (4.4 × 10-8 S cm-1 with Ea = 0.56 eV), indium-doped samples Na6-xâ¡xMg1-xInxS4 (x = 0.05, 0.1) were prepared by the mechanochemical synthesis route. These samples also contained 13% MgO. Their ionic conductivities of 9.3 × 10-8 S cm-1 (Ea = 0.51 eV) and 2.5 × 10-7 S cm-1 (Ea = 0.49 eV) at 25 °C for x = 0.05 and 0.1, respectively, were higher than the ionic conductivity of the undoped sample.
RESUMEN
It is desirable for secondary batteries to have high capacities and long lifetimes. This paper reports the use of Na2 FeS2 with a specific structure consisting of edge-shared and chained FeS4 as the host structure and as a high-capacity active electrode material. An all-solid-state sodium cell that uses Na2 FeS2 exhibits a high capacity of 320 mAh g-1 , which is close to the theoretical two-electron reaction capacity of 323 mAh g-1 , and operates reversibly for 300 cycles. The excellent electrochemical properties of all-solid-state sodium cells are derived from the anion-cation redox and rigid host structure during charging/discharging. In addition to the initial one-electron reaction of Nax FeS2 (1 ≤ x ≤ 2) activated Fe2+ /Fe3+ redox as the main redox center, the reversible sulfur redox further contributes to the high capacity. Although the additional sulfur redox affects the irreversible crystallographic changes, stable and reversible redox reactions are observed without capacity fading, owing to the local maintenance of the chained FeS4 in the host structure. Sodium iron sulfide Na2 FeS2 , which combines low-cost elements, is one of the candidates that can meet the high requirements of practical applications.
RESUMEN
The reaction uniformity of LiCoO2 composite positive electrodes in all-solid-state cells was compared quantitatively by investigating the Raman band shifts corresponding to the state-of-charge (SOC) of LiCoO2. The quantitative SOC analysis was conducted using the Raman imaging data of composite electrodes with smaller or larger solid electrolytes. The electrodes exhibited different reaction uniformity although the cells showed similar initial charge capacities and average SOC. In the case of larger solid electrolytes, most LiCoO2 particles showed higher or lower SOC than the average SOC, and lower battery performance. The quantitative analysis of SOC in each LiCoO2 electrode demonstrated that a variable SOC outside the average SOC resulted in larger irreversible capacity and lower rate performance. The quantitative SOC analysis newly developed in the present study is a useful technique for designing composite electrodes showing higher battery performance.
RESUMEN
A new crystalline lithium-ion conducting material, Li4SnS4 with an ortho-composition, was prepared by a mechanochemical technique and subsequent heat treatment. Synchrotron X-ray powder diffraction was used to analyze the crystal structure, revealing a space group of P63/ mmc and cell parameters of a = 4.01254(4) Å and c = 6.39076(8) Å. Analysis of a heat-treated hexagonal Li4SnS4 sample revealed that both lithium and tin occupied either of two adjacent tetrahedral sites, resulting in fractional occupation of the tetrahedral site (Li, 0.375; Sn, 0.125). The heat-treated hexagonal Li4SnS4 had an ionic conductivity of 1.1 × 10-4 S cm-1 at room temperature and a conduction activation energy of 32 kJ mol-1. Moreover, the heat-treated Li4SnS4 exhibited a higher chemical stability in air than the Li3PS4 glass-ceramic.
RESUMEN
A unique charge/discharge mechanism of amorphous TiS4 is reported. Amorphous transition metal polysulfide electrodes exhibit anomalous charge/discharge performance and should have a unique charge/discharge mechanism: neither the typical intercalation/deintercalation mechanism nor the conversion-type one, but a mixture of the two. Analyzing the mechanism of such electrodes has been a challenge because fewer tools are available to examine the "amorphous" structure. It is revealed that the electrode undergoes two distinct structural changes: (i) the deformation and formation of S-S disulfide bonds and (ii) changes in the coordination number of titanium. These structural changes proceed continuously and concertedly for Li insertion/extraction. The results of this study provide a novel and unique model of amorphous electrode materials with significantly larger capacities.
RESUMEN
All-solid-state batteries have attracted attention because of their high energy density, safety, and long cycle life. Sulfide active materials exhibit high capacities and enable an enhanced energy density in all-solid-state batteries. In this study, we synthesized electrode-electrolyte bifunctional materials in the system Li2S-V2S3-LiX (X = F, Cl, Br, or I) through a mechanochemical process. In addition, the effects of the addition of lithium halides on the electrochemical properties were investigated. All-solid-state batteries with the Li2S-V2S3-LiI electrode showed the highest capacity of 400 mAh g-1 among all the cells, even though their electronic and ionic conductivities were the same. From the point of view of the ionic conductivity and structure of the electrodes during cycling, it was clarified that a high reversible capacity was achieved not only by high ionic and electronic conductivities before cycling but also by maintaining the ionic conductivity even at the deep state of charge. Furthermore, high-loading all-solid-state cells were fabricated using the Li2S-V2S3-LiI materials with a mass loading of 37.3 mg cm-2, exhibiting a high areal capacity of approximately 11.5 mAh cm-2 at 60 °C and good cycle performance.
RESUMEN
Fluoride glasses in the binary system ZrF4-BaF2 were prepared via mechanochemical treatment. The glass-forming region of the ZrF4-BaF2 system obtained using the mechanochemical method was wider than that obtained using the conventional melt-quenching method. The glass-ceramic 60ZrF4·40BaF2 (mol%) sample was obtained by heat treatment and shows a higher conductivity of 1.2 × 10-6 S cm-1 at 200 °C than the pristine glass. This study revealed that mechanochemical treatment was effective for the synthesis of fluoride glasses.
RESUMEN
Sulfide-based all-solid-state Li/S batteries have attracted considerable attention as next-generation batteries with high energy density. However, their practical applications are limited by short-circuiting due to Li dendrite growth. One of the possible reasons for this phenomenon is the contact failure caused by void formation at the Li/solid electrolyte interface during Li stripping. Herein, we studied the operating conditions, such as stack pressure, operating temperature, and electrode composition, that could potentially suppress the formation of voids. Furthermore, we investigated the effects of these operating conditions on the Li stripping/plating performance of all-solid-state Li symmetric cells containing glass sulfide electrolytes with a reduction tolerance. As a result, symmetric cells with Li-Mg alloy electrodes instead of Li metal electrodes exhibited high cycling stability at current densities above 2.0 mA cm-2, a temperature of 60 °C, and stack pressures of 3-10 MPa. In addition, an all-solid-state Li/S cell with a Li-Mg alloy negative electrode operated stably for 50 cycles at a current density of 2.0 mA cm-2, stack pressure of 5 MPa, and temperature of 60 °C, while its measured capacity was close to a theoretical value. The obtained results provide guidelines for the construction of all-solid-state Li/S batteries that can reversibly operate at high current densities.
RESUMEN
The problem of lithium dendrites must be addressed for practical lithium metal all-solid-state batteries. Herein, three-dimensional morphological changes within Li3PS4 electrolyte away from the anode were observed using operando X-ray computed tomography. We revealed that the electronic conduction of decomposition and the electrolyte/void interface cause the lithium deposition within the Li3PS4.
RESUMEN
Interphase formation at the interface between a solid electrolyte and negative electrode is one of the main factors limiting the practical use of all-solid-state sodium batteries. Sulfide-type solid electrolytes with group 15 elements (P and Sb) exhibit high ductility and ionic conductivity, comparable to those of organic liquid electrolytes. However, the electronically conductive interphase formed at the interface between Na3PS4 and sodium metal increases the cell resistance and deteriorates its electrochemical properties. Contrarily, Na3BS3, containing boron as an electrochemically inert element, forms an electronically insulating thin passivate interphase, facilitating reversible sodium plating and stripping. Sodium-metal symmetric cells with Na3BS3 exhibit steady operation over 1000 cycles. Thus, reduction-stable solid electrolytes can be developed by substitution with an electrochemically inert element versus sodium.
RESUMEN
Understanding the differences in the structures and defects in the stable crystalline phase and metastable phase is important for increasing the ionic conductivities of a solid electrolyte. The metastable phase often has higher conductivity than the stable phase. In this study, metastable lithium thiogallate, Li5GaS4, was synthesized via mechanochemistry and stable Li5GaS4 was obtained by heating the metastable phase. The metastable Li5GaS4 sample was found to have an antifluorite-type crystal structure with cationic disorder, while the stable phase was found to have a monoclinic crystal structure, similar to that of another solid electrolyte, Li5AlS4. In both the structures, the Ga3+ cations were surrounded by four S2- anions in tetrahedral coordination. The conductivity of the metastable phase was determined to be 2.1 × 10-5 S cm-1 at 25 °C, which is 1000 times greater than that of the monoclinic phase. The high conductivity of the metastable phase was achieved owing to cation disorder in the crystal structure.
RESUMEN
Sulfide-based solid electrolytes (SEs) exhibiting high ionic conductivity are indispensable battery materials for next-generation all-solid-state batteries. However, sulfide-based SEs have a major drawback in their low chemical stability in air. When exposed to H2O or O2 gas, toxic H2S is generated, and their ionic conductivity considerably declines. However, their degradation mechanism caused by air exposure has not been understood yet. To clarify the degradation process, in this study, we developed a transmission electron microscope (TEM) system to evaluate the air stability of battery materials. Using a vacuum transfer double-tilt TEM holder with a gas-flow system, the in situ observation of the degradation process was conducted for a sulfide-based Li4SnS4 glass ceramic under an air-flow environment. Consequently, electron diffraction (ED) patterns and TEM images could clearly capture morphological changes and the amorphization process caused by air exposure. Moreover, based on the analysis of ED patterns, it is observed that Li4SnS4 is likely to decompose because of the reaction with H2O in air. Therefore, this airtight and air-flow TEM system should be effective in clarifying the process of the deterioration of sulfur-based SEs during exposure to air.
RESUMEN
The application of lithium metal as a negative electrode in all-solid-state batteries shows promise for optimizing battery safety and energy density. However, further development relies on a detailed understanding of the chemo-mechanical issues at the interface between the lithium metal and solid electrolyte (SE). In this study, crack formation inside the sulfide SE (Li3PS4: LPS) layers during battery operation was visualized using in situ X-ray computed tomography (X-ray CT). Moreover, the degradation mechanism that causes short-circuiting was proposed based on a combination of the X-ray CT results and scanning electron microscopy images after short-circuiting. The primary cause of short-circuiting was a chemical reaction in which LPS was reduced at the lithium interface. The LPS expanded during decomposition, thereby forming small cracks. Lithium penetrated the small cracks to form new interfaces with fresh LPS on the interior of the LPS layers. This combination of reduction-expansion-cracking of LPS was repeated at these new interfaces. Lithium clusters eventually formed, thereby generating large cracks due to stress concentration. Lithium penetrated these large cracks easily, finally causing short-circuiting. Therefore, preventing the reduction reaction at the interface between the SE and lithium metal is effective in suppressing degradation. In fact, LPS-LiI electrolytes, which are highly stable to reduction, were demonstrated to prevent the repeated degradation mechanism. These findings will promote all-solid-state lithium-metal battery development by providing valuable insight into the design of the interface between SEs and lithium, where the selection of a suitable SE is vital.
RESUMEN
Long-lasting all-solid-state batteries can be achieved by preventing side reactions in the composite electrodes comprising electrode active materials and solid electrolytes. Typically, the battery performance can be enhanced through the use of robust solid electrolytes that are resistant to oxidation and decomposition. In this study, the thermal stability of sulfide solid electrolytes Li3PS4 and Li4SnS4 toward oxide positive electrode active materials was estimated by investigating the occurrence of side reactions at the electrolyte-electrode interfaces when the composite electrodes are heated in an accelerated aging test: Li4SnS4 showed higher thermal stability because of the suppression of the substitution reaction between S and O. Moreover, thermally stable sulfide solid electrolytes are amenable to an improved cell construction process. The sintering (pelletizing and subsequent heating) of the composite electrodes with Li4SnS4 as the solid electrolyte allowed the manufacture of dense electrodes that exhibited increased ionic conductivity, thereby enhancing the battery performance.
RESUMEN
The dynamic changes of ionic conduction path in the cross-sectional graphite composite electrodes of bulk-type all-solid-state lithium batteries have been monitored using operando confocal microscopic observations for color changes of graphite in response to their stage structures. The ionic conduction path decreased in the cross-sectional direction as cycle numbers increased, with simultaneous capacity degradation. The local reactivity of lithiation and delithiation was evaluated by image analysis considering state-of-charge (SOC) values. Electrode thickness changes were examined from the confocal microscope images obtained in the operando observations. The results revealed that voids and cracks were formed during cycle tests and that the thickness gradually increased. These cracks and voids were one of the main contributors to the limitation of ionic conduction paths in the depth direction. Operando microscopic observation and subsequent image analysis elucidated not only the morphological changes of active materials but also the differences in local SOC changes in the electrode.
RESUMEN
An all-solid-state lithium battery using inorganic solid electrolytes requires safety assurance and improved energy density, both of which are issues in large-scale applications of lithium-ion batteries. Utilization of high-capacity lithium-excess electrode materials is effective for the further increase in energy density. However, they have never been applied to all-solid-state batteries. Operational difficulty of all-solid-state batteries using them generally lies in the construction of the electrode-electrolyte interface. By the amorphization of Li2RuO3 as a lithium-excess model material with Li2SO4, here, we have first demonstrated a reversible oxygen redox reaction in all-solid-state batteries. Amorphous nature of the Li2RuO3-Li2SO4 matrix enables inclusion of active material with high conductivity and ductility for achieving favorable interfaces with charge transfer capabilities, leading to the stable operation of all-solid-state batteries.
RESUMEN
All-solid-state lithium batteries using inorganic sulfide solid electrolytes have good safety properties and high rate capabilities as expected for a next-generation battery. Presently, conventional preparation methods such as mechanical milling and/or solid-phase synthesis need a long time to provide a small amount of the product, and they have difficult in supplying a sufficient amount to meet the demand. Hence, liquid-phase synthesis methods have been developed for large-scale synthesis. However, the ionic conductivity of sulfide solid electrolytes prepared via liquid-phase synthesis is typically lower than that prepared via solid-phase synthesis. In this study, we have controlled three factors: (1) shaking time, (2) annealing temperature, and (3) annealing time. The factors influencing lithium ionic conductivity of Li3PS4 prepared via liquid-phase synthesis were quantitatively evaluated using high-energy X-ray diffraction (XRD) measurement coupled with pair distribution function (PDF) analysis. It was revealed from PDF analysis that the amount of Li2S that cannot be detected by Raman spectroscopy or XRD decreased the ionic conductivity. Furthermore, it was revealed that the ionic conductivity of Li3PS4 is dominated by other parameters, such as remaining solvent in the sample and high crystallinity of the sample.