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Li10GeP2S12 solid electrolytes for all-solid-state batteries were synthesised rapidly through liquid-phase method in 7.5 h.

The galvanostatic cycling test results demonstrate that the Li7P2S8I·10Li4SiO4 has excellent long-term cycling stability in excess of 680 cycles (1370 h), indicating that it is highly compatible with Li anode.

A (100 − x)Li2S·xAlI3 (0 ≤ x ≤ 30) positive electrode was prepared by the planetary ball-milling method for application in all-solid-state Li–S batteries.

3Li2S–1P2S5–xLiI (x = 0, 0.5, 0.9, 1) solid electrolytes were synthesized by liquid-phase shaking methods using ethyl propionate as a reaction medium. The X-ray diffraction results showed that the main phase at both x = 0.9 and 1.0 was Li4PS4I. The highest ionic conductivity at 25 °C was 7.8 × 10−4 S cm−1 for 3Li2S–1P2S5–0.9LiI (Li6.9P2S8I0.9), although it was 6.4 × 10−4 S cm−1 for 3Li2S–1P2S5–1LiI (Li7P2S8I). Despite the lower ionic conductivity of 3Li2S–1P2S5–1LiI (Li7P2S8I), it exhibited a better stability toward Li metal than 3Li2S–1P2S5–0.9LiI (Li6.9P2S8I0.9), indicating that the amount of LiI strongly affects the stability of the electrolyte against Li metal. In addition, 3Li2S–1P2S5–1LiI (Li7P2S8I) was employed in both the cathode composite and separator in the all-solid-state battery in which LiNbO3 coated-LiNi1/3Mn1/3Co1/3O2 and Li were used as cathode and anode, respectively. The all-solid-state battery showed the reversible capacity of approximately 140 mAh g−1, indicating that 3Li2S–1P2S5–1LiI (Li7P2S8I) solid electrolyte is suitable for an all-solid-state Li metal battery.

We evaluated the structural change of the cathode material Li2MnO3 that was deposited as an epitaxial film with an (001) orientation in an all-solid-state battery. We developed an in situ surface X-ray diffraction (XRD) technique, where X-rays are incident at a very low grazing angle of 0.1°. An X-ray with wavelength of 0.82518 A penetrated an ∼2 μm-thick amorphous Li3PO4 solid-state electrolyte and ∼1 μm-thick metal Li anode on the Li2MnO3 cathode. Experiments revealed a structural change to a high-capacity (activated) phase that proceeded gradually and continuously with cycling. The activated phase barely showed any capacity fading. First-principles calculations suggested that the activated phase has O1 stacking, which is attained by first delithiating to an intermediate phase with O3 stacking and tetrahedral Li. This intermediate phase has a low Li migration barrier path in the [001] direction, but further delithiation causes an energetically favorable and irreversible transition to the O1 phase. We propose a mechanism of structural change with cycling: charging to a high voltage at a sufficiently low Li concentration typically induces irreversible transition to a phase detrimental to cycling that could, but not necessarily, be accompanied by the dissolution of Mn and/or the release of O into the electrolyte, while a gradual irreversible transition to an activated phase happens at a similar Li concentration under a lower voltage.

Material characterization that informs research and development of batteries is generally based on well-established ex situ and in situ experimental methods that do not consider the band structure. This is because experimental extraction of structural information for liquid-electrolyte batteries is extremely challenging. However, this hole in the available experimental data negatively affects the development of new battery systems. Herein, we determined the entire band structure of a model thin-film solid-state battery with respect to an absolute potential using operando hard X-ray photoelectron spectroscopy by treating the battery as a semiconductor device. We confirmed drastic changes in the band structure during charging, such as interfacial band bending, and determined the electrolyte potential window and overpotential location at high voltage. This enabled us to identify possible interfacial side reactions, for example, the formation of the decomposition layer and the space charge layer. Notably, this information can only be obtained by evaluating the battery band structure during operation. The obtained insights deepen our understanding of battery reactions and provide a novel protocol for battery design.

Li

Li

In this study, mechanical milling and liquid-phase shaking are used to synthesise 3Li

The performances of next generation all-solid-state batteries might be improved by using multi-valent cation doped Li6PS5Cl solid electrolytes. This study provided solid electrolytes at room temperature using planetary ball milling without heat treatment. Li6PS5Cl was doped with a variety of multivalent cations, where an electrolyte comprising 98% Li6PS5Cl with 2% YCl3 doping exhibited an ionic conductivity (13 mS cm−1) five times higher than pure Li6PS5Cl (2.6 mS cm−1) at 50 °C. However, this difference in ionic conductivity at room temperature was slight. No peak shifts were observed, including in the synchrotron XRD measurements, and the electron diffraction patterns of the nano-crystallites (ca. 10–30 nm) detected using TEM exhibited neither peak shifts nor new peaks. The doping element remained at the grain boundary, likely lowering the grain boundary resistance. These results are expected to offer insights for the development of other lithium-ion conductors for use in all-solid-state batteries.

We have investigated the initial-cycle battery behavior of epitaxial thin films of Li2MnO3-cathodes by employing resonant inelastic X-ray scattering (RIXS) at the O K- and Mn L3-edges. Thin films ( ...

An epitaxial Li2MnO3(001) thin film electrode with layered rock-salt structure was tested in an all-solid-state battery configuration for the first time. Using amorphous Li3PO4 solid electrolyte, g...

We evaluated the structural change of the cathode material Li

The performances of next generation all-solid-state batteries might be improved by using multi-valent cation doped Li

Surface-coated/uncoated epitaxial LiCoO2 film electrodes with (104) orientations were fabricated on SrRuO3(100)/Nb:SrTiO3(100) using pulsed laser deposition. Films with thicknesses of ~18 nm and flat surfaces with roughnesses of less than 1 nm were model systems for clarifying the kinetics of Li-ion transfer at the electrode/electrolyte interface. The Li-ion transfer characteristics at the interface between the LiCoO2 electrode and the electrolyte (LiPF6, ethylene carbonate + diethyl carbonate) were investigated by electrochemical impedance spectrometry. The charge-transfer resistance (Rct) of uncoated LiCoO2 increased from the early cycles when charged/discharged at 3.0–4.2 V. When charged/discharged at 3.0–4.5 V, the Rct of the uncoated LiCoO2 rapidly increased from the first charge. In contrast, the Rct of Li2ZrO3-coated LiCoO2 remained almost constant during the early cycles when charged/discharged either at 3.0–4.2 or at 3.0–4.5 V. The interfacial resistances of the coated and uncoated LiCoO2 electrodes were almost equal (~100 Ω cm2). The activation energy for charge transfer was lower for the coated LiCoO2 electrode compared to that for the uncoated electrode. The current-rate capability was significantly improved by surface coating even at high-voltage charge/discharge at 3.0–4.5 V. The charge transfer process is the rate-determining step of the charge/discharge reaction.

Lithium battery has been used as a power source for not only small devices but also large equipment like an electric vehicle because of its potentially high energy density and high rate performance. All-solid-state battery is a promising battery form to achieve high energy density. Since solid-electrolyte has a wider potential window than a liquid one, high voltage cathode material can be implemented. Among novel cathode materials, we focus on a Li-rich manganese oxide Li2MnO3, which has a layered rock-salt structure with a honeycomb-ordered LiMn2 layer. Although having a high theoretical capacity of ~459 mAh g-1, the cathode delivers a smaller reversible capacity than the theoretical value. Recently, we have found that an all-solid-state battery with a Li2MnO3 thin film can deliver a reversibly capacity of 270 mAh g-1, and the rate and cyclic performance are extremely high [1]. However, the redox species of the Li2MnO3 during the electrochemical charge/discharge reactions are still unknown for this battery system. In this study, the charge compensation mechanism of the Li2MnO3 cathode in an all-solid-state thin film battery was investigated by using an operando hard X-ray photoelectron spectroscopy (HAXPES) method. Although X-ray photoelectron spectroscopy is a powerful method to investigate the electronic structure of the cathode, there is an issue that the probing depth is about a few nm when using Al or Mg Ka source. On the other hand, HAXPES has a high probing depth of several 10 nm, which makes it possible to detect a signal from the buried region of the battery. Solid-electrolyte supported thin film batteries were developed for HAXPES measurement as illustrated in Fig (a). Using solid-electrolyte as substrate, cathode, and anode layers can be separated on the front and the back of the substrate, respectively, which enables us to detect the HAXPES signal of the cathode layer. The battery composed of a polycrystalline Li2MnO3 cathode, an amorphous Li3PO4 buffer layer, a lithium anode, an Al current collector, and a LICGC glass-ceramics solid-electrolyte substrate (manufactured by Ohara Inc.) was prepared by using pulsed laser deposition, magnetron sputtering, and thermal or electron-beam vapor deposition methods. Charge-discharge experiments were performed galvanostatically at a 0.2 C rate between 2.0 and 5.0 V (vs. Li/Li+) at room temperature. After the cell voltage reached at 5.0 V, the voltage was kept for 30 minutes.An operando HAXPES measurement was conducted at BL28XU in SPring-8. The incident photon energy of 7940 eV was used. The operando O1s, Mn3s, and Li1s spectra were measured during the 1st and the 5th charge-discharge processes. The charge-discharge curves showed a plateau at 4.6 V in the 1st charge and slope-like curves from the 1st discharge. Since these characteristics are also identified in the case of the battery using the Li2MnO3 epitaxial thin film [1], the prepared battery is suitable to conduct a HAXPES measurement for the purpose. The figures (b, c) show O1s operando spectra during the 1st charge-discharge process. During the 1st charge, a new peak at 531.1 eV is generated from 3.7 V in addition to a lattice oxygen O2- at 529.8 eV. According to previous reports, the new peak can be assigned as higher oxidized lattice oxygen such as O- [2]. After 3.7 V, the area of the new peak increases while that of O2- decreases as the voltage increases. During the 1st discharge, the new peak gradually decreases and then disappears at 3.3 V. Therefore, the reversible oxygen redox could contribute the charge compensation for the battery reactions. The average valence state of Mn was analyzed from Mn3s operando spectra. Manganese is reduced from 4+ to 3.5+ during the 1st charge process then Mn is further reduced to 3.1+ from 3.3 V during 1st discharging process. Upon the 5th charge-discharge process, the Mn redox occurred reversibly below 3.5 V. These results indicate that the oxygen as well as Mn redox reactions occur reversibly in Li2MnO3 cathode. Furthermore, the oxygen redox occurs on the higher voltage region between ~3.3 and 5.0 V and the Mn redox occurs on the lower region between 2.0 and ~3.3 V. Therefore, it is evident that the large reversible capacity of Li2MnO3 thin film results from the oxygen redox activity. Realizing the stable oxygen redox reaction on batteries with a larger scale will be a key for practical application. [1] K. Hikima et al., Chem. Lett. 48, 192 (2019). [2] M. Sathiya et al., Nature Materials 12, 827 (2013). Figure 1

All-solid-state is an ideal form of batteries. The all-solid-state batteries are also suitable system for elucidating battery reaction using spectroscopic methods. The present study focuses on the reaction mechanism study of lithium excess cathode materials using all-solid-state batteries. The lithium manganese oxide, Li2MnO3, is a model system of the lithium excess layered rock-salt structure. In the present study, the epitaxial and polycrystalline films with 30 nm-thick with various compositions and morphologies were fabricated using pulsed laser deposition and sputtering methods. These electrodes showed charge-discharge capacity ranging from 150 to 300 mAh g-1 with different degradation characteristics depending on the compositions and morphologies. The reaction mechanisms were studied by in-situ and operando methods using surface X-ray diffraction and operando HAXPES analyses. The Li2MnO3 shows a transformation to a high-capacity phase after activation process by the first charge and the degradation during subsequent cycling depends on the sample stoichiometry and morphology. The transition to the high capacity phase is related the phase change from O3 to O1 type, together with interlayer cation disordering on the Li/Mn layer. The activation process is related to the oxidation of oxygen and a formation new oxygen species. The activation process and the reversible reactions of the lithium-rich layered rock-salt materials are elucidated.

Liquid-phase synthesis is a promising method for the large-scale production of sulfide-type solid electrolytes. However, solid electrolytes synthesized by liquid-phase methods exhibit lower conductivity values than those synthesized using solid-state synthesis (e.g., mechanical milling). Li2S-P2S5-LiI solid electrolytes are commonly used in all-solid-state battery applications owing to their high ionic conductivity and chemical stability of lithium. Previous studies have shown that Li2S-P2S5-LiI solid electrolytes (Li2S:P2S5:LiI = 3:1:1) synthesized using the liquid-phase method have lower conductivities (0.35–0.63 mS cm−1) than those synthesized via solid-state synthesis (1.35 mS cm−1). The ionic conductivity of Li2S-P2S5-LiI solid electrolytes obtained via liquid-phase synthesis may be improved by optimizing the drying conditions. Our study observed that the Li2S-P2S5-LiI solid electrolytes dried below 130 °C under vacuum and at 170 °C under ambient pressure exhibited an increased ionic conductivity of 1.0 mS cm−1, which is comparable to that of Li2S-P2S5-LiI solid electrolytes obtained via solid-state synthesis. X-ray diffraction patterns revealed that the intensities of the new crystalline phase were higher than those of the Li4PS4I phase; in addition, a lower weight loss was observed in the thermogravimetry curve measurements. These results indicated that the drying step at 170 °C under an ambient pressure could promote removal of organic solvent from complex and new phase formation, thereby contributing to improved ionic conductivity. Our study provides important guidance for the optimization of liquid-phase synthesis with the aim of achieving high ionic conductivity.

The reaction mechanism of lithium excess manganese oxide, Li2MnO3, with layered rock-salt structure was examined using model thin film electrodes with liquid or solid electrolytes. The epitaxial or polycrystalline films with 30 nm-thick with various compositions and morphologies were fabricated using pulsed laser deposition and sputtering methods. These electrodes showed charge-discharge capacity ranging from 150 to 300 mAh g-1with different degradation characteristics depending on the compositions and morphologies. The reaction mechanisms were studied by in-situ and operando methods using surface X-ray diffraction and HAXPES analyses. The Li2MnO3shows a transformation to a high-capacity phase after the activation process by the first charge and the degradation during the subsequent cycling depends on the sample stoichiometry and morphology. The transition to the high capacity phase is related the phase change from the O3 to O2 type, together with the interlayer cation disordering on the Li/Mn layer. The activation process is related to the oxidation of oxygen and a formation new oxygen species together with the reduction of the manganese from tetra-valent state. The activation process and the reversible reactions of the lithium-rich layered rock-salt materials are elucidated.

Lithium-rich layered rock-salt type Li2MnO3 is one of the most attractive cathode materials for lithium batteries because it achieved the high discharge capacities of 250−300 mAh g-1 after activation during the first cycling [1]. However, the structural deterioration in the following cycles at the cathode/liquid electrolyte interface leads to severe capacity fading. We reported that the Li2MnO3 films on solid system exhibit a high capacity of 250 mAh g–1 and better cycle stability, although liquid system showed severe capacity degradation [2]. To elucidate the activation process and high capacity phase contributing to high cycle stability, crystal structure changes at activation process were analyzed using the different initial structure of Li2MnO3. The initial structure was controlled by stacking solid electrolyte using two types of synthesis methods. The Li2MnO3 electrode films were synthesized on SrRuO3/SrTiO3(111) substrates by pulsed laser deposition (PLD). Amorphous Li3PO4 as the solid electrolyte was synthesized by PLD and magnetron sputtering. Lithium metal was used as the negative electrode, respectively. The crystal structure changes at activation process were analyzed by in situ X-ray diffraction (XRD) measurements. The Li2MnO3 structure had layered rock-salt type structure after stacking Li3PO4 by using PLD. On the other hand, in case of stacking by using magnetron sputtering, the Li2MnO3 changed disordered structure with the transition metal (TM) layer disordering of lithium and manganese ions in the honeycomb lattice. For the Li2MnO3 with layered rock-salt type structure, the discharge capacity increased continuously in the following cycles with persisting plateau region for several cycles. On the other hand, the Li2MnO3 with disordered structure showed about 300 mAh g–1 at the first cycle. The XRD intensity ratio of I 020/I 001 was zero after activation at both of initial structures [3]. Since the 020 peak arises from a superlattice structure by a honeycomb-type ordered arrangement of Li and Mn atoms in the TM layer, atomic arrangements in the TM layer transformed to a disordered state. This high capacity phase could contribute to its high capacity and cycle stability. Acknowledgment: This work was supported by the Research and Development Initiative for Scientific Innovation of New Generation Batteries 2 (RISING2) of the New Energy and Industrial Technology Development Organization (NEDO). References: [1] M. Sathiya et al., Nat. Mater., 2013, 12, 827-835.[2] K. Hikima et al., The 57th battery symposium in Japan, 2016, 2G22. [3] K. Hikima et al., The 58th battery symposium in Japan, 2017, 2C22.

Structures, electrochemical properties and reaction mechanism of lithium rich layered cathode materials, Li2 MO3 (M = transition metals), were studied for the epitaxial-films fabricated by pulsed laser deposition methods. Their charge-discharge characteristics were investigated both for the liquid and solid electrolyte systems and the lithium intercalation-deintercalation reactions were studied using surface X-ray diffraction and hard X-ray photoelectron spectroscopy. The charge-discharge capacities drastically increased with decreasing film thickness for the Li2MnO3 using liquid electrolyte. The 12.6 nm thick film showed higher capacity over 300 mA h g-1 and better stability compared to the 29.8 and 47.8 nm thick films. The dependence of the electrochemical properties on the film thickness demonstrates that the surface region is actively reconstructed to generate a high capacity phase with high electrochemical stability. The structure analysis also indicated that the surface structural changes at the initial cycling have a pronounced effect on the power characteristics and the capacity of lithium-rich layered rocksalt type cathodes. On the other hand, the Li2MnO3 using solid electrolytes showed higher charge-discharge capacity and better stability after 100 cycles than the liquid system. Surface structure analysis indicates a different phase change during the cycling from the liquid system. The reactions at the solid/solid interface could contribute to the phase changes at the surface region and also to the cycling degradation of these lithium rich phases.