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Cerium species are added to membrane electrode assemblies (MEAs) of polymer electrolyte fuel cells as radical quenchers to suppress the degradation caused by radical species derived from the reaction between impurity and hydrogen peroxide formed during fuel cell operation [1]. During long-term operation, the radical quencher of the dissolved trivalent cerium ions moves toward the cathode electrolyte interface, which negatively affects the durability of the fuel cell. To clarify the transport phenomena of radical quenchers, composition mapping analysis of disassembled cells after degradation test has been mainly performed. However, to estimate the quantitative value such as mobility and diffusion coefficient, it is necessary to directly observe the transport phenomena of cerium species under operating conditions of fuel cells. In the previous report, cerium ion transport with in-plane direction has analyzed using X-ray fluorescence mapping [2]. Compared with the in-plane analysis, operando analysis of cerium distribution with through-plane in MEA is challenge due to the quite thin thickness of electrolyte membrane. In this study, we have developed a technique for cerium ion mapping with through-plane MEA under fuel cell operation using high-energy micro-beam X-ray fluorescence spectroscopy. This technique is applied to analyze the transport phenomena of radical quenchers with through-plane MEA in 2nd-generation MIRAI fuel cells. The fluorescence X-ray measurements were conducted at BL37XU of SPring-8. Monochromatized X-ray of 45 keV was focused to less than 200 nm by Kirkpatrick-Baez mirror. The X-rays were incident vertically from the membrane thickness direction, and the X-ray fluorescence spectra were measured using a Ge detector. MEAs used in the 2nd-generation MIRAI were cut and sandwiched placed in custom made carbon separators and end-plates. The effective electrode area is 1.0 cm2. Ce-Ka fluorescence X-ray was monitored under fuel cell operation at 60°C by supplying humidified hydrogen and oxygen gases. In the open circuit condition, cerium is mainly detected in anode MPL and cathode MPL, while there is low concentration of cerium in PEM. This is consistent with the report of the elemental analysis for 1st-generation MIRAI [3]. During fuel cell operation at 1.0 A cm-2, the part of concentrated concentration shifts toward to cathode side. The enriched cerium in anode MPL is slightly shaved from the anode catalyst layer. We obtained the time-resolved cerium concentration profile, which can be used to estimate the apparent diffusion coefficient of cerium. Acknowledgment This work is based on results obtained from the project commissioned by the New Energy and Industrial Technology Development Organization (NEDO) of Japan. MEAs were provided by Toyota Motor Corporation. References [1] E. Endoh, N. Onoda, Y. Kaneko, Y. Hasegawa, S. Uchiike, Y. Takagi, T. Take, ECS Electrochem. Lett., 2 F73-F75 (2013). [2] A.M. Baker, S.K. Babu, R. Mukundan, S.G. Advani, A.K. Prasad, D. Spernjak, R.L. Borup, J. Electrochem. Soc., 164 F1272-F1278 (2017). [3] R.L. Borup, K.L. More, D.J. Myers, FC-PAD: Fuel Cell Performance and Durability Consortium Update to USCAR Analysis of Toyota Mirai Components Provided by USCAR, https://www.osti.gov/servlets/purl/1440417.

Fluoride-ion conducting solid materials are applicable as solid electrolytes for sensing devices and next generation rechargeable batteries. Most of the previously reported materials have limited to the single-anion compounds such as fluorite-type, tysonite-type, and perovskite-type structures. These are suffered from further improvements by crystal structure modification which derives a paradigm shift in the material tailoring. Fluoride and sulfide ions prefer respective coordination environments because of the different ionic radii and electronegativity. This feature implies that fluorosulfide mixed-anion compounds have potential to form anion-ordering crystal structures with new fluoride-ion conducting layers. Herein, we have found that the fluorosulfide La2+xSr1−xF4+xS2 exhibits fluoride ion conduction. The presence of multiple anions results in the formation of anion-ordering two-dimensional crystal lattice with triple fluorite layers, which cannot be realized for metal fluorides. Sulfide ions in the crystal structure increases the number of interstitial sites of fluoride ions, forming fluoride ion conduction pathway.

The effects of applied pressure on the morphological structure of the composite electrode and electrochemical properties of an all-solid-state battery (ASSB) cell are analysed by X-ray computed tomography.

The electrification of heavy-duty transport and aviation will require new strategies to increase the energy density of electrode materials1,2. The use of anionic redox represents one possible approach to meeting this ambitious target. However, questions remain regarding the validity of the O2-/O- oxygen redox paradigm, and alternative explanations for the origin of the anionic capacity have been proposed3, because the electronic orbitals associated with redox reactions cannot be measured by standard experiments. Here, using high-energy X-ray Compton measurements together with first-principles modelling, we show how the electronic orbital that lies at the heart of the reversible and stable anionic redox activity can be imaged and visualized, and its character and symmetry determined. We find that differential changes in the Compton profile with lithium-ion concentration are sensitive to the phase of the electronic wave function, and carry signatures of electrostatic and covalent bonding effects4. Our study not only provides a picture of the workings of a lithium-rich battery at the atomic scale, but also suggests pathways to improving existing battery materials and designing new ones.

All-solid-state fluoride-ion batteries (FIBs) are regarded as attractive alternatives to traditional energy storage systems because of their high energy density; however, they are not applicable at...

Extensive studies on trirutile Li0.5FeF3 phase have been commissioned in the context of the Li–Fe–F system for Li-ion batteries. However, progress in electrochemical and structural studies has been...

The mixed-anion fluorosulfide Yb3F4S2 was examined as a solid electrolyte for all-solid-state fluoride-ion batteries. The synthesized Yb3F4S2 compound by solid-state reaction under vacuum contained...

Experimental characterization of the nanostructure of metastable functional materials has attracted significant attention with recent advances in computational materials discovery. However, since metastable glass-ceramics are easily damaged by irradiation, damage-free nanoimaging has not been realized thus far. Herein, we propose novel high-contrast coherent diffractive imaging that quantitatively analyzes the intact internal nanostructure of metastable glass-ceramics using femtosecond X-ray pulses. The immersion of sample particles in a solvent helps enhance the reconstructed image contrast and allows us to distinguish an ∼7% electron density difference between an amorphous form and crystals. Furthermore, morphological operations with a band-pass filter quantitatively elucidate the depth information. The evaluated volume ratio of the amorphous to crystalline phases is ∼2.5:1 for the measured metastable (Li

With the increasing development of electric vehicles and portable devices, there is a strong requirement for high-energy batteries. To improve battery energy, multielectron transfer electrode react...

Owing to its low cost, thermal stability, and theoretically high capacity, Li2FeSiO4 has been a promising cathode material for high-energy-density Li-ion (Li+) battery systems. However, its poor ra...

An all-solid-state battery in which the organic liquid electrolyte of a lithium-ion battery (LIB) is replaced with an inorganic solid electrolyte is a candidate for next-generation rechargeable batteries. Although the solid electrolyte has high conductivity, the charge and discharge characteristics are inferior to those of conventional LIBs. To achieve the high performance of all-solid-state batteries, it is necessary to grasp the phenomena peculiar to the composite electrode that uses the solid electrolyte. This study analyses the three-dimensional structure of the composite electrode in an all-solid-state battery using a laboratory-built cell capable of performing electrochemical and X-ray computed tomography (CT) measurements while monitoring stack pressures. The dependencies of stack pressure on the porosity, contact area, and tortuosity of the composite electrodes are quantitatively analysed to evaluate their effects on the electrochemical properties. The CT observation reveals that there is insufficient contact between the active material and the solid electrolyte in a plane perpendicular to the pressure direction. The contact interface is found to be a key parameter for the charge/discharge characteristics.

Honeycomb layered oxides with monovalent or divalent, monolayered cationic lattices generally exhibit myriad crystalline features encompassing rich electrochemistry, geometries and disorders, which particularly places them as attractive material candidates for next-generation energy storage applications. Herein, we report global honeycomb layered oxide compositions, ${\rm Ag_2}M_2{\rm TeO_6}$ ($M = \rm Ni, Mg, \textit{etc}.$) exhibiting $\rm Ag$ atom bilayers with sub-valent states within Ag-rich crystalline domains of ${\rm Ag_6}M_2{\rm TeO_6}$ and $\rm Ag$-deficient domains of ${\rm Ag}_{2 - x}\rm Ni_2TeO_6$ ($0 < x < 2$). The $\rm Ag$-rich material characterised by aberration-corrected transmission electron microscopy reveals local atomic structural disorders characterised by aperiodic stacking and incoherency in the bilayer arrangement of $\rm Ag$ atoms. Meanwhile, the global material not only displays high ionic conductivity, but also manifests oxygen-hole electrochemistry during silver-ion extraction. Within the $\rm Ag$-rich domains, the bilayered structure, argentophilic interactions therein and the expected $\rm Ag$ sub-valent states ($1/2+, 2/3+, \textit{etc}.$) are theoretically understood via spontaneous symmetry breaking of SU($2$)$\times$U($1$) gauge symmetry interactions amongst $3$ degenerate mass-less chiral fermion states, justified by electron occupancy of silver $4d_{z^2}$ and $5s$ orbitals on a bifurcated honeycomb lattice. This implies that bilayered frameworks have research applications that go beyond the confines of energy storage., 67 pages, 5 figures, 1 cover art, 1 table

Water management is important for stable operation of PEFCs (Polymer Electrolyte Fuel Cells), since the proton conductivity depends on water content and excessive water hinders electrochemical reactions. As the durability of PEFC has become a major issue, the correlative behavior between liquid water and cerium oxides (radical scavengers) is drawing much attention. Till now, the water content and its inhomogeneous distributions have been reported by neutron radiography and X-ray computed tomography (CT). In this paper, we present a high-energy Compton scattering imaging (CSI) technique for non-destructive observation of liquid water in PEFC. The advantage of high-energy CSI over X-ray CT is that the CSI technique has direct access to a two-dimensional cross section inside a PEFC without its rotation. The radiation damage on polymer electrolyte membranes is negligibly small since the photoelectric absorption is substantially reduced at such high-energy X-rays. Although high-energy X-ray CT is not sensitive to light-element materials, X-ray Compton scattering has its sensitivity to light elements. Figure 1 shows the cross-sectional images of GDL (Gas Diffusion Layer) materials and liquid water [1]. The GDL materials are made of porous carbon fibers and carbon composites with Teflon treatment, TGP-H-300 (TORAY Industries, Inc., Tokyo, Japan). The area of the cross sections is 2mm x 2mm, and its thickness is 10μm. The spatial resolution is 75 μm. Figure 1(a) shows the image of dry GDL materials, displaying the distribution of carbon fibers and carbon composite, and Figure 1(b) does the difference image between dry and wet, representing the liquid water distribution. Negative contributions are observed in the carbon fiber and carbon composite region, which indicates possible interactions between the GDL materials and liquid water. In this presentation, applications to a model cell under operation are also presented, together with correlation mappings of liquid water and cerium. The capability of CSI for vehicles’ PEFCs (TOYOTA MIRAI) is also discussed. This work was performed under the NEDO FC-Platform project. [1] N. Tsuji et al., Appl. Sci. 11, 3851 (2021) Figure Caption: Fig.1: Cross-sectional images of GDL materials and liquid water. Figure 1

Suntivich et al. found a volcano relationship between the eg occupancy in perovskite oxide and OER activity. eg filling of ~ 1.2 is the optimum value1. Nevertheless, some materials do not follow this trend. A typical example is oxides containing a high valence Ni(4+) state. To elucidate the effect of high-valence Ni on OER activity, it is necessary to evaluate the OER activity of materials with stable Ni in a high oxidation state (4+). However, in case of the perovskite family, the formation of Ni4+ requires calcination under high oxygen partial pressures (60-200 bar). In contrast, LiNi0.5Mn1.5O4 (LNMO) with a spinel structure is known that lithium ions are desorbed by oxidation to produce tetravalent nickel ions quantitatively. Therefore, by using this material as an oxygen-evolving electrode, it is possible to quantitatively evaluate the activity of tetravalent nickel ions. Herein, we report the OER activity of nickel-manganese spinel, in which Ni4+ was stable up to the bulk. LiNi0.5Mn1.5O4 powder was synthesized as follows. Stoichiometric amounts of LiNO3, Ni(NO3)2.6H2O, and Mn(NO3)2.6H2O were dissolved in ultrapure water. A four-to-five-fold molar excess of citric acid was added while stirring. This solution was heated at 400 °C to obtain the precursor. The obtained powder was calcined at 800 °C for 12 h and at 700 °C for 48 h under pure O2. Various levels of chemical delithiation were achieved by reacting LiNi0.5Mn1.5O4 with nitronium tetrafluoroborate in acetonitrile solution for 48 h at 25 ºC. The degree of delithiation was controlled by changing the ratio of LiNi0.5Mn1.5O4 to NO2BF4. The suspension of LiNi0.5Mn1.5O4 and NO2BF4 was stirred for 48 h to obtain a uniform particle composition. Subsequently, the suspension was filtered, thoroughly washed with acetonitrile at least three times, and dried overnight in a vacuum oven. Then, chemical composition was determined using inductively coupled plasma optical emission spectrometry, X-ray diffraction (XRD) patterns were collected in BL02B2 at SPring-8, Japan. XAS was conducted for Mn and Ni K-edges, XAS for Mn, Ni L-edges, and O K-edge was also conducted. This study focused on the electrocatalytic activity of LixNi0.5Mn1.5O4 spinels with different lithium contents. The lithium (x) content in LixNi0.49Mn1.51O4 was controlled by topochemical delithiation using NO2BF4 in an acetonitrile solution. Upon applying this approach, nickel changed from the divalent to tetravalent state, while the tetravalent state of manganese was maintained. The OER activity was found to increase with decreasing x. x = 0.00 showed the highest OER activity. The Tafel slopes indicated that the RDS changed from OH− adsorption to proton transfer from OH*; thus, the OER kinetics was enhanced. The XAS spectra of Ni and O indicated that the presence of Ni4+ caused a downshift in the unoccupied Ni 3d state and decreased the energy barrier of charge transfer from the oxygen intermediate species to the metal active site; hence, the OER activity was enhanced. This study revealed the mechanism underpinning the high OER activity of high-valence Ni(4+) and also provided a approach for the development of highly active catalyst materials, namely, topochemical delithiation. Acknowledgement This work is based on results obtained from a project (JPNP14021) commissioned by the New Energy and Industrial Technology Development Organization (NEDO) of Japan. References Suntivich, J.; May, K. J.; Gasteiger, H. A.; Goodenough, J. B.; Shao-Horn, Y., Science 2011, 334, 1383-1385. Ren Y. et al., ACS Appl. Energy Mater. 2021 4 (10), 10731-10738

1. Introduction Lithium-sulfur (Li-S) batteries are rechargeable devices assembled with a sulfur cathode and a lithium metal anode. Li-S batteries have twice the volumetric energy density and 5 times the gravimetric energy density of lithium-ion batteries (LIB). Hence, Li-S batteries are expected to be applied to stationary power sources and EV vehicles [1]. However, Li-S batteries have the following issues: ・Sulfur and the final discharge product (Li2S) are insulators. ・In the discharge process, sulfur expands up to 1.8 times, so the structure of batteries is unstable. ・Intermediate products (Li2Sx (x = 4 – 8)) dissolve in an electrolyte; Li2Sx (x = 4 – 8) diffused to an anode to provide an insulating layer at the anode surface. ・In the charge process, Li2Sx (x = 4 – 8) causes redox shuttling. As a result, Li-S batteries cannot charge and discharge stably. In order to deal with this problem, Nazar et al. reported the method that sulfur is confined in porous carbon [2]. This approach provides a cathode realizing good electronic conductivity, restriction of sulfur expansion, and suppression of Li2Sx (x = 4 – 8) dissolution. Although these improved characteristics allow Li-S batteries to operate, The discharge capacity of Li-S batteries is still not high enough and this needs to be addressed. In our previous study, we reported that oxidation treatment to microporous carbon (MC) with HNO3 improves Li-S batteries' discharge capacity [3]. Moreover, we clarified that the discharge capacity of Li-S batteries has an approximate proportional relation with the amount of oxygen-containing functional groups on the MC surface [4]. This work attempts to elucidate the mechanism of improved Li-S battery performance by oxidation treatment to MC. Our report would lead to the proposal of a novel strategy to improve the performance of Li-S batteries. 2. Method 2.1 Preparation of Oxidized MC-Sulfur composite (Ox MC-S) MC was added into 69 wt.% HNO3 and refluxed at 120ºC for 2 h. By vacuum filtration and washing with deionized water, Ox MC was obtained. Ox MC dried in vacuum at 80ºC overnight was mixed with sulfur at a weight ratio of Ox MC: S = 48: 52. The mixture was thermally annealed at 155ºC for 5 h (Ox MC-S). Untreated MC was also composited with sulfur by the same method (MC-S). 2.2 Assembling of Cells Each MC-S cathode was prepared by mixing the MC-S, acetylene black, carboxymethyl cellulose, and styrene butadiene rubber at a respective weight ratio of 89: 5: 3: 3 and coating the resulting aqueous slurry on an Al foil current collector. The cells with the MC-S electrode and Li metal foil as an anode were assembled in a glove box filled with Ar. Lithium bis(trifluorosulfonyl)imide (LiTFSI): tetraglyme (G4): hydrofluoroether (HFE) = 10: 8: 40 (by mol) was used as the electrolyte. 2.3 Electrochemical Impedance Spectroscopy (EIS) To elucidate the effect of oxidation treatment on the internal resistance of Li-S batteries, EIS was carried out at various potentials (Discharge 2.0 – 1.0 V and Charge 1.0 – 3.0 V). The obtained Nyquist plots were used for the evaluation of solid electrolyte interphase (SEI) resistance (Rsei), charge-transfer resistance (Rct), and Warburg impedance (Rw). Rw was investigated with the calculation of Warburg coefficient (σ). 3. Major results and conclusion Since oxidation treatment to MC significantly increased the discharge capacity of Li-S batteries [3][4], it was expected that oxidation treatment would lower the internal resistance of Li-S batteries. EIS of MC-S and Ox MC-S at various potentials showed that oxidation treatment reduced Rsei by an average of 12.2 Ω. This indicates that the SEI thickness was reduced, or the SEI was composed of highly ion-conductive components by the oxidation treatment. Rct decreased only at lower potentials, and the Warburg coefficient decreased except at the end of charge and discharge potential. These results suggest that the oxidation treatment decreases overall resistance, but especially SEI resistance and Warburg impedance, which may improve the discharge capacity of Li-S batteries. We will also report the activation energy of Rsei and Rct and mechanism analysis of decreasing Rsei by oxidation to MC. This work was supported by “Advanced Low Carbon Technology Research and Development Program, Specially Promoted Research for Innovative Next Generation Batteries (ALCA-SPRING [JPMJAL1301])” from JST. [1] Y. Guo et al., Angew. Chem. Int. Ed., 52 (2013) 13186. [2] X. Ji et al., Nat. Mater., 8 (2009) 500. [3] S. Okabe et al., Electrochemistry, 85 (2017) 671. [4] L. Yoshida et al., ECS 238th PRiME Meeting Abstracts (2020).

Hydroxyl and hydroperoxyl radicals produced by reacting impurities with hydrogen peroxide is one of the degradation factors of polymer electrolyte [1]. A method to suppress this degradation is the addition of cerium into the polymer electrolyte membrane (PEM), which serves as radical quencher [2,3]. However, cerium ion in PEM migrates from the initial state by fuel cell operation [4]. The lack of cerium ion in PEM causes degradation from radical species. Information on cerium migration in PEM is necessary to design the membrane electrode assembly (MEA) for long-term operation. Although the observation of cerium ion diffusion with in-plane direction of PEM has been reported [5], it is difficult to detect the distribution in through-plane of MEA under fuel cell operating condition due to the quite narrow thickness of PEM. This study reports an operando X-ray fluorescence analysis technique to detect cerium distribution in through-plane direction of MEA using high-energy X-ray nanobeam. MEAs were prepared by a conventional method using Pt/C catalyst and polymer electrolyte with the thickness of 12 mm. The active electrode area was 1 cm2. Single cells were assembled using custom-made end-plates that have an X-ray permeation window. Operando X-ray fluorescence spectroscopy measurements were performed at SPring-8, BL37XU (Japan). The monochromatized X-ray at an energy of 45 keV was focused to less than 200 nm by Kirkpatrick-Baez mirror. To detect the cerium distribution in MEA, Ce-Ka fluorescence intensity was counted using a Ge semiconductor detector with scanning the position of the cell. The cell temperature was 80 ℃. O2 and H2 gases with relative humidity of 100% were flew to cathode and anode, respectively. Figure 1 shows line-scan profile of Ce-Kα fluorescence X-ray intensity from the as-prepared MEA. The x-axis represents the through-plain position, where the positive and negative sides corresponds to cathode and anode sides, respectively. The two peaks are observed at 678 and 685 mm and the peak width is approximately 13 mm. This peak shows PEM containing cerium ion. During the fuel cell operation, the line-scan is repeated and cerium ion distribution can be analyzed. Acknowledgment Part of this work is based on results obtained from the project commissioned by the New Energy and Industrial Technology Development Organization (NEDO) of Japan. [1] R. Borup et al., Chem. Rev., 107 3904-3951 (2007). [2] E. Endoh et al., ECS Electrochem. Lett. 2 F73-F75 (2013). [3] P. Trogadas et al., Electrochem. Solid-State Lett. 11 B113-B116 (2008). [4] S.M. Stewart et al., ECS Electrochem. Lett. 3 F19-F22 (2014). [5] A.M. Baker et al., J. Electrochem. Soc. 164 F1272-F1278 (2017). Figure 1

The use of core–shell nanoparticles composed of metal core (Mc, representing Pd, Au, Ru, etc.) and quasi-monolayer Pt shell (Ptqms) facilitates the achievement of cost and activity targets in many ...

The charge/discharge capacity of current lithium-ion battery cathode materials is limited by the charge compensation of transition-metal redox during the charge/discharge processes. Recently, the u...

Owing to their high theoretical capacity, metal fluorides have attracted significant interest as materials for fabricating the cathode of lithium secondary batteries. In the present study, a nanocomposite of LiF and FeF2 is prepared by a fluorolytic sol–gel method in an ethanol solution, for use as the cathode material of a lithium secondary battery. The produced LiF/FeF2 composite is characterized by broad X-ray diffraction peaks attributed to the nanosized (∼10 nm) LiF and FeF2 crystals, a large Brunauer–Emmett–Teller surface area of 119 m2 g-1, and adsorption–desorption hysteresis, attributed to the presence of mesopores. The results of charge–discharge tests indicates an initial discharge capacity of 225 mAh (g-LiF/FeF2)−1 through reversal conversion at a current rate of 10 mA (g-LiF/FeF2)−1. Based on a combination of galvanostatic intermittent titration, X-ray absorption, and X-ray diffraction investigations, a new reaction mechanism is developed, namely, the conversion of the local environment of an Fe atom from a rutile-type FeF2 structure to a rhenium trioxide-type FeF3 structure during charging, with the subsequent discharge resulting in the insertion of Li+ into the rhenium trioxide-type FeF3 structure, followed by the conversion reaction to LiF and FeF2.

In sheet-type all-solid-state lithium-ion batteries with the sulfide-based solid electrolyte, composite electrodes consist of active material, solid electrolyte, conductive additive material, and b...

Zero-strain insertion materials are ideal electrode materials for lithium-ion batteries because they do not undergo dimensional change during lithium insertion and extraction. Herein, a zero-strain insertion material, Ni-substituted Li2Co2O4 (Li2Ni0.2Co1.8O4) having a spinel framework, was synthesized and characterized to study the zero-strain mechanism. The change in the lattice dimensions of Li2Ni0.2Co1.8O4 during lithium extraction was very small (only 0.1%), confirming that Li2Ni0.2Co1.8O4 is a zero-strain insertion material. It had a flat voltage profile at 3.5 V with a reversible capacity of 100 mA h g−1, which was quite different from the voltage profile of LiCoO2 having a layered structure. Detailed structural analysis by X-ray absorption spectroscopy revealed that there was no dimensional change because the changes in two crystallographic factors, contraction of the Co–O bond and distortion of the oxygen sublattice, cancelled out. The zero-strain lithium-ion battery combined with Li2Ni0.2Co1.8O4 and Li[Li1/3Ti5/3]O4 showed good cyclability.

International audience; The reactivity of water with Li-rich layered Li2RuO3 and partial exchange of Li2O with H2O within the structure is studied under aqueous (electro)chemical conditions. Upon slow delithiation in water over long time periods, micron-sized Li2RuO3 particles structurally transform from an O3 structure to an O1 structure with a corresponding loss of 1.25 Li ions per formula unit. The O1 stacking of the honeycomb Ru layers is imaged using high-resolution high-angle annular dark-field scanning transmission electron microscopy, and the resulting structure is solved by X-ray powder diffraction and electron diffraction. In situ X-ray absorption spectroscopy suggests that reversible oxidation/reduction of bulk Ru sites is realized on potential cycling between 0.4 and 1.25 VRHE in basic solutions. In addition to surface redox pseudocapacitance, the partially delithiated phase of Li2RuO3 shows high capacity, which can be attributed to bulk Ru redox in the structure. This work demonstrates that the interaction of aqueous electrolytes with Li-rich layered oxides can result in the formation of new phases with (electro)chemical properties that are distinct from the parent material. This understanding is important for the design of aqueous batteries, electrochemical capacitors, and chemically stable cathode materials for Li-ion batteries.

The electrification of heavy-duty transport and aviation will require new strategies to increase the energy density of electrode materials

A high-capacity positive electrode active material Li2RuO3-Li2SO4 for all-solid-state batteries was developed., 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.

Owing to its low cost, thermal stability and theoretically high capacity, Li2FeSiO4 has been a promising cathode material for high-energy-density Li-ion (Li+) battery system. However, its poor rate performance and high voltage polarisation attributed to innately slow Li+ kinetics at room temperature, has fundamentally curbed its ascent into prominence. Here, the rate performance of Li2FeSiO4 at high temperatures in electrolyte comprising molten salt (ionic liquid) was investigated. Subsequently, a comparison of the phase transition behaviour observed at both high-temperature and room-temperature cycling was elucidated. Our results show that remarkable rate performance with good cyclability in conjunction with low voltage polarisation is attained upon cycling of Li2FeSiO4 at high temperatures, due to the faster phase transformation from unstable monoclinic structures to thermodynamically stable orthorhombic structures triggered by elevated temperature. What this study adds to the burgeoning body of research work relating to the silicates is that the initially slow phase transformation behaviour observed at room temperature can significantly be enhanced upon cycling at elevated temperatures.

International audience; Rechargeable batteries using multivalent metals are among the most promising next-generation battery systems due to their high capacity, high safety, and low cost compared with lithium-ion batteries. However, strong cation−anion interaction degrades diffusion in solid cathodes, an effect that must be mitigated to yield practical multivalent metal batteries. We show that a highly defective iron phosphate−carbon composite prepared by ultracentrifugation serves as a reversible insertion/deinsertion for magnesium ions with, and operates beyond, a 2-V cell voltage at room temperature. A composite of noncrystalline particles that embeds the surrounding carbon structure enhances the magnesium-ion diffusion in the solid phase with stability for cycle life. X-ray absorption spectroscopy, transmission electron microscopy with energy-dispersive X-ray spectroscopy, and high-energy X-ray scattering measurements demonstrate magnesium-ion insertion and extraction in the defective iron phosphate without conversion reactions. This work suggests promising applications for highly defective structures as intercalation hosts for multivalent ions.

The key to improving the performance of lithium-ion batteries is to precisely elucidate the temporal and spatial hierarchical structure of the battery. Lithium-ion batteries consist of cathodes and anodes and a separator containing an electrolyte. The cathodes and anodes of lithium-ion batteries are made of a composite material consisting of an active material, a conductive material, and a binder to form a complex three-dimensional structure. The reaction proceeds as lithium ions are repeatedly inserted into and removed from the active material. Therefore, the lattice of the active material is restructured due to ion diffusion, which results in phase change. At the active material–electrolyte interface, the insertion and de-insertion of lithium ions proceed with the charge transfer reaction. The charge–discharge reaction of a lithium-ion battery is a nonequilibrium state due to the interplay of multiple phenomena. Analysis after disassembling a battery, which is performed in conventional battery research, does not provide an accurate understanding of the dominant factors of the reaction rate and the degradation mechanism, in some cases. This review introduces the results of research on the temporal and spatial hierarchical structure of lithium-ion batteries, focusing on operando measurements taken during charge–discharge reactions. Chapter 1 provides an overview of the hierarchical reaction mechanism of lithium-ion batteries. Chapter 2 introduces the operando measurement technique, which is useful for analysis. Chapter 3 describes the reaction at the electrode–electrolyte interface, which is the reaction field, and Chapter 4 discusses the nonequilibrium structural change caused by the two-phase reaction in the active material. Chapter 5 introduces the study of the unique reaction heterogeneity of a composite electrode, which enables practical energy storage. Understanding the hierarchical reaction mechanism will provide useful information for the design of lithium-ion batteries and next-generation batteries.

Introduction of an interlayer between a cathode and a sulfide solid electrolyte is a well-known method for reducing the interfacial resistance and improving the performance of all-solid-state batteries. However, the mechanism responsible for the interlayer remains unclear because it is difficult to observe the reactions at the nanometer-scale range. In this study, thin-film model interface of LiCoO2/80Li2S·20P2S5 and LiCoO2/Li3PO4/80Li2S·20P2S5 are fabricated by pulsed-laser deposition. The model interfaces are investigated by performing electrochemical measurements and depth-resolved X-ray absorption spectroscopy to clarify the effect of the Li3PO4 interlayer. The results indicate that a reaction product layer forms between the LiCoO2 cathode and the 80Li2S·20P2S5 electrolyte during charge/discharge processes, resulting in high interfacial resistance. Meanwhile, the formation of the reaction product layer can be suppressed by the introduction of a Li3PO4 interlayer.

High rate capability is one of the most important properties in Li-ion batteries for electric vehicle and/or energy grid use. Herein, a high-power electrode material consisting of dual-substituted LiFePO4 by zirconium and silicon, Li(Fe0.95Zr0.05)(P0.9Si0.1)O4, was developed as it exhibits small lattice volume change between Li-rich and Li-poor phases. The dual-substituted cathode exhibited 1.1–4.4 times larger charge/discharge capacities for upper 10 C rates than that of the undoped material. Time-resolved XRD measurements at the high rate of 10 C revealed the formation of a metastable intermediate phase during the Li intercalation/deintercalation processes which triggers the continuous phase transition in Li(Fe0.95Zr0.05)(P0.9Si0.1)O4 with moderation of the lattice mismatch. Controlling the lattice volume change between the initial and end phase of the intercalation materials is key to achieving high rate capabilities.

Mechanism of magnesium ion alloying reaction into bismuth electrode in magnesium bis(trifluoromethanesulfonyl)amide (Mg(TFSA)2)/acetonitrile (AN) and Mg(TFSA)2/2-methyltetrahydrofuran (2-MeTHF) ele...

Rechargeable potassium-ion batteries have been gaining traction as not only promising low-cost alternatives to lithium-ion technology, but also as high-voltage energy storage systems. However, their development and sustainability are plagued by the lack of suitable electrode materials capable of allowing the reversible insertion of the large potassium ions. Here, exploration of the database for potassium-based materials has led us to discover potassium ion conducting layered honeycomb frameworks. They show the capability of reversible insertion of potassium ions at high voltages (~4 V for K2Ni2TeO6) in stable ionic liquids based on potassium bis(trifluorosulfonyl) imide, and exhibit remarkable ionic conductivities e.g. ~0.01 mS cm−1 at 298 K and ~40 mS cm–1 at 573 K for K2Mg2TeO6. In addition to enlisting fast potassium ion conductors that can be utilised as solid electrolytes, these layered honeycomb frameworks deliver the highest voltages amongst layered cathodes, becoming prime candidates for the advancement of high-energy density potassium-ion batteries. The development of potassium-ion batteries requires cathode materials that can maintain the structural stability during cycling. Here the authors have developed honeycomb-layered tellurates K2M2TeO6 that afford high ionic conductivity and reversible intercalation of large K ions at high voltages.

Delafossite oxides (ABO2) have a layered structure with alternating layers of A and B elements, the topmost layer of which appears to determine their performance, such as the oxygen evolution reaction (OER) activity. In this study, we investigated the topmost layer of single-domain (0 0 1)-oriented AgCoO2 epitaxial thin film for potential use as an OER catalyst. The thin film was confirmed to possess OER activity at a level comparable to the catalyst in powder form. Atomic scattering spectroscopy revealed the topmost layer to be composed of CoO6 octahedra. In situ X-ray absorption spectroscopy showed that the oxidation of Co at the surface did not change under different potentials, which suggests that there is no valence fluctuation of Co in the stable CoO6 octahedral structure. However, the oxidation number of Co at the surface was lower than that in the bulk. Our density functional theoretical calculations also showed the Co atoms at the surface to have a slightly higher electron occupancy than those in the bulk, and suggests that the unoccupied t2g states of Co at the surface have an influence on OER activity.