Lithium-Ion Conducting Haloboro-Oxysulfides

Abstract

Described are a solid material which has ionic conductivity for lithium ions, a process for preparing said solid material, a use of said solid material as a solid electrolyte for an electrochemical cell, a solid structure selected from the group consisting of a cathode, an anode and a separator for an electrochemical cell, and an electrochemical cell comprising such solid structure.

Claims

1. A solid material having a composition according to general formula (I)
Li.sub.2x+zB.sub.2yM.sub.aO.sub.b*aS.sub.x+3yX.sub.z  (I) wherein M is one or more selected from the group consisting of P, Si, Ge, As and Sb X is one or more selected from the group consisting of halides and pseudohalides x is in the range of from 0.1 to 0.7 y is in the range of from 0.05 to 0.5 z is in the range of from 0.01 to 0.5 a is in the range of from 0.01 to 0.5 b is in the range of from 1.9 to 2.6 0.995≤x+y+z+a≤1.005.

2. The solid material according to claim 1, wherein said solid material having a composition according to general formula (I) is glassy.

3. The solid material according to claim 1, wherein M is selected from the group consisting of Si, P and Sb and/or X is selected from the group consisting of Cl, Br and I.

4. The solid material according to claim 1, wherein M is Si and X is selected from the group consisting of Cl, Br and I.

5. The solid material according to claim 1, having a composition according to general formula (Ia)
Li.sub.2x+zB.sub.2ySi.sub.aO.sub.b*aS.sub.x+3yI.sub.z  (Ia) wherein x is in the range of from 0.1 to 0.3 y is in the range of from 0.1 to 0.25 z is in the range of from 0.2 to 0.48 a is in the range of from 0.08 to 0.5 b is in the range of from 1.95 to 2.05 0.995≤x+y+z+a≤1.005.

6. The solid material according to claim 1, wherein the solid material has an ionic conductivity of 0.1 mS/cm or more.

7. The solid material according to claim 1, wherein the solid material is in the form of a sheet.

8. A process for preparing a solid material as defined in claim 1, said process comprising a) providing the precursors Li.sub.2S B.sub.2S.sub.3 or both of boron and sulfur one or more oxides of elements M selected from the group consisting of P, Si, Ge, As and Sb one or more compounds LiX wherein X is selected from the group consisting of halides and pseudohalides b) preparing a mixture comprising the precursors provided in a, wherein in said mixture the molar ratio of the elements Li, S, B, M, O and X matches general formula (I) c) heat-treating the mixture to obtain a melt d) quenching the melt so that a solid material having a composition according to general formula (I) is obtained.

9. The process according to claim 8, wherein the precursors provided in a) are Li.sub.2S, S, B, SiO.sub.2 and one or more of LiCl, LiBr and LiI and/or in b) mixing is performed by means of mechanical milling and/or in c) heat-treating is performed in a closed vessel and/or in d) quenching is performed by contacting the melt with water, ice, a sub-cooled gas, a metal plate or a chemically inert mold.

10. The process according to claim 8, wherein c) comprises a first stage of heat-treating at a temperature in the range of from 400° C. to 650° C. for a duration of 1 to 13 hours, and a second stage of heat treating at a temperature in the range of from 700° C. to 1000° C., preferably in the range of from 700° C. to 900° C. for a duration of from 1 to 40 hours.

11. The process according to claim 9, wherein in b) the mixture comprising the precursors is formed into pellets, which are heat-treated in c).

12. The process according to claim 9, wherein in b) any handling is performed under a protective gas atmosphere.

13. The solid material according to claim 1, for use as a solid electrolyte for an electrochemical cell, wherein preferably the solid electrolyte is a component of a solid structure for an electrochemical cell selected from the group consisting of cathode, anode and separator.

14. A solid structure for an electrochemical cell, wherein said solid structure is selected from the group consisting of cathode, anode and separator, wherein the solid structure comprises a solid material according to claim 1.

15. An electrochemical cell comprising a solid material wherein preferably the solid material is a component of a solid structure as defined in claim 14.

Description

EXAMPLES

[0129] 1. Preparation of Materials

[0130] Step a)

[0131] The following precursors were provided.

[0132] (1) Li.sub.2S (Sigma Aldrich, 99.98%)

[0133] (2) boron (Sigma Aldrich 99%) and sulfur, both in elemental form

[0134] (3) SiO.sub.2

[0135] (4) LiI.

[0136] Step b)

[0137] Mixtures of the precursors provided in step a) were prepared by grounding the precursors together in such amounts that in the obtained mixture the molar ratio of the elements Li, S, B, M, O and X matches general formula (I).

[0138] For comparison, mixtures were prepared without adding SiO.sub.2.

[0139] Each mixture was pelletized.

[0140] All handling of powders was carried out in an argon-filled glove box.

[0141] Step c)

[0142] For heat treating each pelletized mixture obtained in step b) was placed in a glassy carbon crucible which was placed in a quartz tube. Each quartz tube was sealed under vacuum and placed vertically in a furnace. The tubes were heated up to 500° C. and held for 12 hours, then at 800° C. for 20 hours.

[0143] Step d)

[0144] After heat treating was completed the obtained melts were quenched in ice water.

[0145] The obtained materials were in powder form. For details of the composition of the obtained materials, see the table below.

[0146] 2. Ionic Conductivity and Electronic Conductivity

[0147] The bulk resistance of samples of the obtained solid materials was determined by electro-chemical impedance spectroscopy with an amplitude of 100 mV in the frequency range 10 MHz to 100 mHz using a Bio-logic MTZ-35 impedance analyzer. The measurements were carried out in the temperature range of from 25° C. to 80° C. The samples were obtained by pelletizing the powder material in a 10 mm diameter custom-made Swagelok cell. For recording the impedance spectra, a sample was sandwiched between two indium foils in order to obtain good contact at variable temperatures. Lithium ion conductivity was calculated from the bulk resistance of the sample.

[0148] The lithium ion conductivity measured at 25° C. of all samples is given in tables 1 and 2 below:

TABLE-US-00001 TABLE 1 Ionic Conductivity (mS/cm) with standard SiO.sub.2 I deviation of 5 content content measurements Composition a z per sample LiB.sub.0.5SI.sub.0.5 0 0.5 0.64 ± 0.03 Li.sub.0.91B.sub.0.46Si.sub.0.09O.sub.0.18S.sub.0.91I.sub.0.46 0.09 0.46 0.55 ± 0.01 Li.sub.0.83B.sub.0.42Si.sub.0.17O.sub.0.34S.sub.0.83I.sub.0.42 0.17 0.42 0.43 ± 0.01 Li.sub.0.81B.sub.0.4Si.sub.0.2O.sub.0.4S.sub.0.8I.sub.0.4 0.2 0.4 1.96 ± 0.04 Li.sub.0.77B.sub.0.39Si.sub.0.23O.sub.0.46S.sub.0.77I.sub.0.39 0.23 0.39 1.59 ± 0.04 Li.sub.0.71B.sub.0.36Si.sub.0.29O.sub.0.58S.sub.0.71I.sub.0.36 0.29 0.36 1.60 ± 0.02 Li.sub.0.67B.sub.0.33Si.sub.0.33O.sub.0.67S.sub.0.67I.sub.0.33 0.33 0.33 1.07 ± 0.02 Li.sub.0.5B.sub.0.25Si.sub.0.5OS.sub.0.5I.sub.0.25 0.5 0.25 0.093 ± 0.002

TABLE-US-00002 TABLE 2 Ionic Conductivity (mS/cm) with standard SiO.sub.2 I deviation of 5 content content measurements Composition a z per sample Li.sub.1.06B.sub.0.48S.sub.1.02I.sub.0.46 0 0.46 0.525 ± 0.005 Li.sub.0.94B.sub.0.43Si.sub.0.11O.sub.0.22S.sub.0.91I.sub.0.41 0.11 0.41 1.58 ± 0.04 Li.sub.0.85B.sub.0.38Si.sub.0.2O.sub.0.4S.sub.0.82I.sub.0.37 0.2 0.37 2.08 ± 0.03 Li.sub.0.77B.sub.0.35Si.sub.0.27O.sub.0.55S.sub.0.74I.sub.0.33 0.27 0.33 1.38 ± 0.02 Li.sub.0.71B.sub.0.32Si.sub.0.33O.sub.0.67S.sub.0.68I.sub.0.31 0.33 0.31 1.04 ± 0.01 Li.sub.0.65B.sub.0.30Si.sub.0.38O.sub.0.77S.sub.0.63I.sub.0.28 0.38 0.28 0.916 ± 0.006 Li.sub.0.61B.sub.0.27Si.sub.0.43O.sub.0.86S.sub.0.58I.sub.0.26 0.43 0.26 0.941 ± 0.011 Li.sub.0.57B.sub.0.26Si.sub.0.47O.sub.0.93S.sub.0.54I.sub.0.25 0.47 0.25 0.434 ± 0.006 Li.sub.0.53B.sub.0.24Si.sub.0.50OS.sub.0.51I.sub.0.23 0.5 0.23 0.183 ± 0.004

[0149] In tables 1 and 2 “I content” means the content of iodine (I).

[0150] The data in the tables and FIG. 1 (plot of ionic conductivity vs the SiO.sub.2 content for the materials of table 2) show that the ionic conductivity is significantly influenced by the SiO.sub.2 content (parameter “a” of formula (Ia)). Addition of small amounts of SiO.sub.2 results in a significant increase of the ionic conductivity. Without wishing to be bound by theory this effect is attributed to improved glass formation due to the presence of the secondary glass network former SiO.sub.2, compared to the SiO.sub.2-free comparison material Li.sub.1.06BB.sub.0.48S.sub.1.02I.sub.0.46. After passing a maximum and then after a slight decrease remaining on a quite high level, the ionic conductivity finally decreases significantly when the SiO.sub.2 content is increased further.

[0151] In addition, as can be seen from the tables, increasing the LiX content results in increased ionic conductivity.

[0152] The electronic conductivity was determined via DC polarization using a 10 mm diameter custom-made cell, where powder was pressed between two stainless steel pistons. A voltage of 0.125, 0.25, 0.5, and 0.75 V, resp., was applied for 1 hour for each measurement. For Li.sub.0.85B.sub.0.38Si.sub.0.20O.sub.0.4S.sub.0.82I.sub.0.37 (the material exhibiting the highest ionic conductivity) an electronic conductivity of 5.93*10.sup.−9 S/cm was determined, which is more than five orders of magnitude lower than the ionic conductivity (2.05 mS/cm, cf. table 2).

[0153] 3. X-Ray Diffraction

[0154] For recording the XRD pattern, a powder sample was placed on a zero background holder and sealed with Kapton film. The diffraction pattern was measured in Bragg-Brentano geometry on a Pan Analytical Empryean X-ray diffractometer using Cu K-alpha radiation, in the range of 5 degrees two-theta to 90 degrees two-theta.

[0155] FIG. 2 shows XRD patterns of a set of samples with varying SiO.sub.2 content a (for details of the composition, cf. table 2 above).

[0156] For this set of samples, the glass forming domain extends from a=0.2 to a=0.43, as evident from the absence of sharp reflexes in the XRD patterns. When the SiO.sub.2 content a is outside this range, the material can be regarded as a composite, due to the emergence of reflexes originating from secondary phases resp. impurity phases observed in the XRD patterns.

[0157] The decline of the sharp reflexes of LiI secondary phases when the SiO.sub.2 content a increases from 0 to 0.2 apparently indicates that the poor glass network forming of the SiO.sub.2-free comparison material is significantly improved already by a small amount of SiO.sub.2. The better the glass network forming the more LiI is incorporated into the glass network, resulting in vanishing of the reflections of LiI secondary phases (cf. FIG. 2) and in an increase of the ionic conductivity (cf. FIG. 1).

[0158] It is assumed that LiI is almost completely dissolved into the glass matrix since the XRD patterns of materials wherein a is in the range of from 0.2 to 0.43 (the glass forming domain) exhibit not reflections or extremely weak reflections only.

[0159] At an SiO.sub.2 content a of 0.43, reflections of LiI and SiO.sub.2 emerge in the XRD pattern which become more pronounced with increasing SiO.sub.2 content (cf. FIG. 2). Apparently, LiI and SiO.sub.2 start to crystallize out of the glass network. Beyond a=0.43, the samples behave more like nanocomposites, likely containing crystalline SiO.sub.2 and LiI nanodomains which disrupt the lithium ion conducting paths and cause a significant drop in conductivity (cf. FIG. 1).

[0160] As evident from FIG. 1 samples having a composition falling in the glass forming domain exhibit favorable ionic conductivity, with a maximum of the ionic conductivity at an SiO.sub.2 content a=0.23 corresponding to the lower limit of the glass forming domain. The decrease of the lithium ion conductivity with further increase of the SiO.sub.2content within the glass forming domain is probably due to the correlated decrease of the fraction of LiI relative to the gross composition.

[0161] While addition of further SiO.sub.2 within the glass forming domain is not advantageous in view of the ionic conductivity, it may be advantageous in view of chemical stability (see below).

[0162] 4. Stability Against Air

[0163] Samples were obtained by pressing 100 mg of powder material into 10 mm diameter pellets. For testing the stability against air, the sample was placed in a three-necked round bottom flask. An air pump was run in reverse in order to flow ambient air into the three-neck round bottom flask. The second neck of the flask contained a probe that was directly connected to an H.sub.2S sensor (BW GasAlertMicro 5 Multi-Gas Detector). The probe was placed directly above the sample in order to ensure accurate H.sub.2S monitoring. The third neck was used as an exhaust/outlet port. The air temperature was approximately 23-25° C. with a relative humidity of 40-50%. The H.sub.2S evolution from the samples upon air exposure was monitored for approximately 3 hours.

[0164] For comparison, samples of β-Li.sub.3PS.sub.4 (prepared by solution processing, cf. WO 2018/054709 A1), and of Li.sub.7P.sub.3S.sub.11 and were tested, too.

[0165] Results of the test are shown in FIG. 3.

[0166] As anticipated, Li.sub.7P.sub.3S.sub.11 exhibited poor stability, showing rapid H.sub.2S evolution at levels greater than 10 ppm in the first 5 minutes. The experiment was curtailed after 100 minutes because the H.sub.2S level reached more than 200 ppm which surpassed the limits of the detector. In contrast, β-Li.sub.3PS.sub.4 exhibited no observable H.sub.2S evolution. This is likely the result of residual solvent in the material due to its low processing temperatures that aids in stabilizing the material under the presence of moisture in the atmosphere.

[0167] In contrast, a sample of the composition Li.sub.0.77B.sub.0.39Si.sub.0.23O.sub.0.46S.sub.0.77I.sub.0.5 showed 5 ppm H.sub.2S evolution for 3 hours, and a sample of the composition Li.sub.0.5B.sub.0.25Si.sub.0.5OSI.sub.0.25 showed nearly identical low H.sub.2S evolution like β-Li.sub.3PS.sub.4, except for a transient increase to 2 ppm H.sub.2S noted after 1 hour of air exposure. However, the composition Li.sub.0.5B.sub.0.25Si.sub.0.5OSI.sub.0.25 exhibits inferior lithium ion conductivity.

[0168] Apparently the increase of the number of silicate groups provides an increase in the chemical stability with a tradeoff in the ionic conductivity.

[0169] It has to be noted that the experiments conducted here are indicative of somewhat extreme conditions while lithium-ion batteries are typically processed under dry-room conditions with significantly less moisture (<1% relative humidity). Thus, the thioiodoborosilicates studied here appear promising because it may be reasonably expected that they evolve little to no H.sub.2S within the time limits required for battery assembly.

[0170] 5. Microscopy

[0171] Scanning Electron Microscopy images and accompanying Energy Dispersive X-ray Analysis (EDX) of particles of Li.sub.0.85B.sub.0.38Si.sub.0.2O.sub.0.4S.sub.0.82I.sub.0.37 (the material exhibiting the highest ionic conductivity) (not shown) as well as scanning transmission electron microscopy (STEM) analysis accompanied by electron energy loss spectra (EELS) (not shown) indicted that the studied materials exhibit a high degree of homogeneity of elemental dispersion on the submicron scale.

[0172] 6. Thermal Stability

[0173] An amount of 5 to 10 mg of solid material was loaded into an aluminum pan and hermetically sealed in an argon filled glovebox with a Tzero sample press. Differential scanning calorimetry (DSC) was conducted using a TA Instruments Q2000 DSC under nitrogen flow. Samples were heated at a rate of 5° C./min from 25° C. to 500° C.

[0174] The thermal stability of a glass can be characterized by the softening (glass transition) temperature (T.sub.g) and by the stability against crystallization, which is determined by the temperature difference between the temperature of the onset of crystallization (T.sub.x) and the glass transition temperature (T.sub.g).

[0175] The glass transition temperature (T.sub.g), the temperature of the onset of crystallization (T.sub.x) and the melting temperature T.sub.l of a couple of materials are compiled in table 3. T.sub.g corresponds to the temperature where the highest slope in the drop of the DSC baseline occurs before the exothermic crystallization peak. T.sub.x corresponds to the onset of crystallization from LiI which recrystallizes out of the glass network. Recrystallization of LiI was confirmed by XRD (not shown). T.sub.l does not correspond to the melting of the glass itself but to the melting of LiI which was previously recrystallized from the glass.

[0176] It can be seen from table 3 that increase of the SiO.sub.2 content from a=0 to a=0.2 results in an increase of T.sub.g and a more significant increase of T.sub.x and T.sub.l. Further increase of the SiO.sub.2 content to a=0.27 results in a further increase of T.sub.x while T.sub.g and T.sub.l change only slightly. Due to the stronger increase of T.sub.x in contrast to T.sub.g, increase of the SiO.sub.2 content from a=0 to a=0.27 results in an increase of the thermal stability parameter, ΔT.sub.x (T.sub.x-T.sub.g), implying that increase of the SiO.sub.2 content results in increased stability of the glass network with respect to recrystallization. Further increase of the SiO.sub.2 content to a=0.33 results in some decrease of T.sub.g and T.sub.x, while T.sub.l and the thermal stability parameter change only slightly.

TABLE-US-00003 TABLE 3 Summary of T.sub.g, T.sub.x, T.sub.l, and calculated thermal stability parameters thermal glass onset tem- melting stability SiO.sub.2 transition perature of temper- parameter content temperature crystallization ature T.sub.l ΔT.sub.x = T.sub.x − T.sub.g, composition (a) T.sub.g (° C.) T.sub.x (° C.) (° C.) (° C.) Li.sub.1.06B.sub.0.48S.sub.1.02I.sub.0.46 0 267 272 374 5 Li.sub.0.85B.sub.0.38Si.sub.0.2O.sub.0.4S.sub.0.82I.sub.0.37 0.2 307 330 430 23 Li.sub.0.77B.sub.0.35Si.sub.0.27O.sub.0.55S.sub.0.74I.sub.0.33 0.27 306 341 428 35 Li.sub.0.71B.sub.0.32Si.sub.0.33O.sub.0.67S.sub.0.68I.sub.0.31 0.33 299 335 429 36

[0177] 7. Electrochemical Studies

[0178] Li.sub.0.85B.sub.0.38Si.sub.0.2O.sub.0.4S.sub.0.82I.sub.0.37 (the material exhibiting the highest ionic conductivity) was subject to electrochemical studies.

[0179] Interfacial reactivity of solid electrolytes in contact with lithium metal was evaluated using a combination of electrochemical impedance spectroscopy (EIS) in conjunction with galvanostatic cycling measurements of symmetric Li|solid electrolyte|Li cells wherein the solid electrolyte is either Li.sub.0.85B.sub.0.38Si.sub.0.2O.sub.0.4S.sub.0.82I.sub.0.37 (according to the invention) or β-Li.sub.3PS.sub.4 (for comparison). The symmetric cells were assembled in a glovebox filled with an argon atmosphere. The solid electrolyte was pressed under a load of 2 tons for 1 min in a 10 mm diameter PEEK cylinder to form a pellet having a thickness of around 0.12 mm. Li metal foil (Sigma Aldrich) was pressed on either side of the pellet in contact with the solid electrolyte. This assembly Li-foil|solid electrolyte|Li-foil was sandwiched between two stainless steel rods and held under pressure using a custom-made device. The cell was tightened with a torque wrench set at a torque of 4 N.Math.m. Galvanostatic cycling of the cells was performed at room temperature using a Bio-Logic VMP-3. The cell according to the invention was galvanostatically cycled at a current density of 0.1 mA/cm.sup.2 to an areal capacity of 0.1 mAh/cm.sup.2. The comparison cell was galvanostatically cycled at a current density of 0.1 mA/cm.sup.2 to an areal capacity of 0.05 mAh/cm.sup.2. Simultaneously the resistance of each cell was measured every 5 cycles using electrochemical impedance spectroscopy at an applied voltage of 100 mV. FIG. 4 shows the development of the cell resistance with increasing cycling time (measured every 5 cycles). The upper graph relates to the comparison cell, and the lower one to the cell according to the invention.

[0180] The cell according to the invention exhibits stable cycling (stripping/plating of lithium) for 110 hours with one-tenth the polarization voltage (10 mV) of the comparison cell (100 mV). This difference in large part owes to the significantly higher ionic conductivity of Li.sub.0.85B.sub.0.38Si.sub.0.2O.sub.0.4S.sub.0.82I.sub.0.37 compared to β-Li.sub.3PS.sub.4. The resistance of the comparison cell appears to fluctuate but increases over cycling. The increase of the resistance of the comparison cell is known in the art for β-L.sub.i3PS.sub.4. see e.g. Z. Liu, W. Fu, E. A. Payzant, X. Yu, Z. Wu, N. J. Dudney, J. Kiggans, K. Hong, A. J. Rondinone, C. Liang, J. Am. Chem. Soc. 2013, 135, 975, and may be attributed to the formation of a passivating interphase composed of Li.sub.2S and Li.sub.3P which is known in the art, see e.g. K. N. Wood, K. X. Steirer, S. E. Hafner, C. Ban, S. Santhanagopalan, S. H. Lee, G. Teeter, Nat. Commun. 2018, 9, 2490. Because of its formation of a passivating interphase, β-Li.sub.3PS.sub.4 has been widely regarded as one of the most stable solid-electrolytes in contact with Li metal, in comparison to other state of the art solid electrolytes, see e.g. S. Wenzel, D. A. Weber, T. Leichtweiss, M. R. Busche, J. Sann, J. Janek, Solid State Ionics 2016, 286, 24; S. Wenzel, S. Randau, T. Leichtweiβ, D. A. Weber, J. Sann, W. G. Zeier, J. Janek, Chem. Mater. 2016, 28, 2400; and S. Wenzel, T. Leichtweiss, D. Krüger, J. Sann, J. Janek, Solid State Ionics 2015, 278, 98. In contrast, the cell according to the invention does not show a significant increase of the resistance over cycling. This effect may be attributed the incorporation of LiI in the solid electrolyte of the cell according to the invention.

[0181] Battery cycling tests were carried out with an all solid state cell comprising an anode made of an Li—In alloy, a solid electrolyte layer (separator) made of Li.sub.0.85B.sub.0.38Si.sub.0.2O.sub.0.4S.sub.0.82I.sub.0.37 and a cathode comprising a composite prepared by mixing the solid electrolyte Li.sub.0.85B.sub.0.38Si.sub.0.2O.sub.0.4S.sub.0.82I.sub.0.37 and TiS.sub.2 (Sigma Aldrich, 99.9%, particle size 75 μm) in a 1:1 weight ratio. The cathode composite (8 mg; TiS.sub.2 content corresponding to 5.13 mg/cm.sup.2), and the solid electrolyte (60 mg) were pressed in a 10 mm diameter PEEK cylinder to form a bilayer pellet. The Li—In alloy of the anode has a target composition Li.sub.0.5In and was formed by pressing a lithium foil and an indium foil in a 0.5 molar ratio, and placed in contact with the solid electrolyte. The cell was then sandwiched between two stainless steel rods and held under pressure using a custom-made device. The cell was allowed to rest for 8 hours before cycling in order to allow for pressure relaxation of the cell. The areal capacity of the cell was 1.2 mAh/cm.sup.2. Galvanostatic cycling (charging/discharging) of the cell was performed at room temperature using a Bio-Logic VMP-3. The cell was charged and discharged at C/10 in the voltage range 0.9 to 2.4 V vs. Li—In (1.5 to 3 V vs. Li) at room temperature (−25° C.).

[0182] The charge-discharge curves of cycles 1, 2, 5, 10, 20 and 50 are shown in FIG. 5. Upon the first charging cycle at 2.7 V vs. Li, a tiny irreversible capacity (6 mAh/g) is evident that is attributed to initial electrolyte oxidation at the cathode interface. The potential at which this irreversible capacity is observed is similar to what has been observed in thiophosphate-based electrolytes, where S.sup.2− undergoes oxidation, see e.g. W. D. Richards, L. J. Miara, Y. Wang, J. C. Kim, G. Ceder, Chem. Mater. 2015, 28, 266; and R. Koerver, F. Walther, I. Aygün, J. Sann, C. Dietrich, W. G. Zeier, J. Janek, J. Mater. Chem. A 2017, 5, 22750. This irreversible process occurring in the first charging cycle is more clearly seen in the corresponding dQ/dV plots shown in FIG. 6. The peak at 2.15 V vs. Li-In exhibits a rapid drop in intensity after the first cycle and completely disappears by the tenth cycle, suggesting the formation of a stable cathode-electrolyte interface.

[0183] After the first cycle, the cell shows excellent cycling performance at C/10 (upper graph in FIG. 7), with virtually no capacity fade over three months of cycling. The cell maintains a capacity of ˜239 mAh/g (theoretical capacity of TiS.sub.2: 240 mAh/g) for more than 130 cycles with high coulombic efficiency of 99.9% on average (lower graph in FIG. 7).

[0184] Rate capabilities of an identical all-solid-state cell cycled within the same voltage range and at 25° C. are shown in FIG. 8. Initially, the cell cycled at C/5 achieves a capacity of 213 mAh/g, which represents 90% capacity retention on doubling the current density. On subsequent increase of the current density to a 1 C rate, 75% of the capacity is retained and the capacity is fully recovered upon returning to the initial C/5 rate.