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Coupled with anionic and cationic redox chemistry, Li-rich/excess cathode materials are prospective high-energy-density candidates for the next-generation Li-ion batteries. However, irreversible lattice oxygen loss would exacerbate irreversible transition metal migration, resulting in a drastic voltage decay and capacity degeneration. Herein, a metastable layered Li-excess cathode material, T2-type Li0.72[Li0.12Ni0.36Mn0.52]O2, was developed, in which both oxygen stacking arrangement and Li coordination environment fundamentally differ from that in conventional O3-type layered structures. By means of the reversible Li migration processes and structural evolutions, not only can voltage decay be effectively restrained, but also excellent capacity retention can be achieved upon long-term cycling. Moreover, irreversible/reversible anionic/cationic redox activities have been well assigned and quantified by various in/ex-situ spectroscopic techniques, further clarifying the charge compensation mechanism associated with (de)lithiation. These findings of the novel T2 structure with the enhanced anionic redox stability will provide a new scope for the development of high-energy-density Li-rich cathode materials.

Most research on the electrochemical dynamics in materials for high-energy Li-ion batteries has focused on the global behavior of the electrode. This approach is susceptible to misleading analyses resulting from idiosyncratic kinetic conditions, such as surface impurities inducing an apparent two-phase transformation within LiNi 0.8Co0.15Al0.05O2 . Here, we use nano-focused X-ray probes to measure delithiation operando at the scale of secondary particle agglomerates in layered cathode materials during charge. After an initial latent phase, individual secondary particles undergo rapid, stochastic, and largely uniform delithiation, which is in contrast with the gradual increase in cell potential. This behavior reproduces across several layered oxides. Operando X-ray microdiffraction (µ-XRD) leverages the relationship between Li content and lattice parameter to further reveal that rate acceleration occurs between Li-site fraction (xLi) ~0.9 and ~0.4 for LiNi0.8Co0.15Al0.05O2 . Physics-based modeling shows that, to reproduce the experimental results, the exchange current density (i0) must depend on xLi , and that i0 should increase rapidly over three orders of magnitude at the transition point. The specifics and implications of this jump in i0 are crucial to understanding the charge-storage reaction of Li-ion battery cathodes.

Heterogenous architectures with elemental gradients tailored within particles have been pursued to combat the instabilities limiting Ni-rich cathode materials for lithium-ion batteries. The growth of different compositional layers is accomplished during the synthesis of hydroxide precursors. However, the extent to which these concentration gradients are modified during high-temperature reactions is difficult to establish in their intact, spherical form. Here, we show the entire three-dimensional structure of a secondary particle can be resolved non-destructively with differential X-ray absorption spectroscopy (XAS) through transmission X-ray microscopy (TXM). The relationship between particle location and elemental content was fully quantified, with high statistical significance, for heterostructures possessing different compositional gradients in the precursors with 90:5:5 Ni:Mn:Co core compositions. Reduced elemental heterogeneity was observed after high-temperature synthesis, but gradients remained. The methodology presented should be used to guide synthesis while assuring that gains in electrochemical performance are linked to precise elemental distributions at the nanoscale.

Magnesium batteries have attracted great attention as an alternative to Li-ion batteries but still suffer from limited choice of positive electrode materials. V2O5 exhibits high theoretical capacities, but previous studies have been mostly limited to α-V2O5. Herein, we report on the β-V2O5 polymorph as a Mg intercalation electrode. The structural changes associated with the Mg2+ (de-) intercalation were analyzed by a combination of several characterization techniques: in situ high resolution X-ray diffraction, scanning transmission electron microscopy, electron energy-loss spectroscopy, and X-ray absorption spectroscopy. The reversible capacity reached 361 mAh g-1, the highest value found at room temperature for V2O5 polymorphs., The authors are grateful to the ALBA synchrotron for beamtime (proposal 2021024935). The Spanish Agencia Estatal de Investigación Severo Ochoa FUNFUTURE (CEX2019-000917-S) Excellence Centre distinction, the European Union’s Horizon 2020 research and innovation programme under grant agreement 824066 (E-MAGIC), and Junta de Andalucía (EMERGIA programme, grant 00153) are gratefully acknowledged. G.C.B.A., P.P., R.F.K., and J.C. were solely supported by the Joint Center for Energy Storage Research (JCESR) and Energy Innovation Hub funded by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences. I.R. acknowledges support from the National Science Foundation via grant DMR-2118020. This research used resources of the National Synchrotron Light Source II, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Brookhaven National Laboratory under Contract DE-SC0012704. The authors acknowledge the free distribution of VESTA software, With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).

The Na-O-Li configurations in P2-type sodium layered transition metal (TM) oxide cathode can trigger additional oxygen redox at high charging voltage (deep de-sodiation). However, the P-type to O-type phase transition and irreversible TM migration would be simultaneously aggravated at high state-of-charge, resulting in structural distortion. Herein, we demonstrate that excessive de-sodiation of Na0.67Li0.1Fe0.37Mn0.53O2 (NLFMO) induces Li removal from lattice and the formation of neighboring O-stacking faults with an OP4-O2 intergrowth structure, which is the chief culprit of structural distortion. Regulating Li migration from the pristine TM layer (LiTM) to the alkali-metal layer (LiAM) would sustain a repetitive P-stacking state (not evolve into a deteriorated neighboring O-stacking), and tune the reversible movement of TM ions during cycling. Accurately regulating the O/P-intergrowth structure (within the OP4 boundary phase) does not bring any obvious trade-off on capacity, but enhances the structural stability of NLFMO cathode, achieving a long-life 165 Wh/kg pouch-cell with cationic/anionic redox activities.

Compared with the polycrystal (PC) Ni-rich cathode materials, the single-crystal (SC) counterpart displayed excellent structural stability, high reversible capacity and limited voltage decay during cycling, which received great attention from academics and industry. However, the origin of fascinating high-voltage stability within SC is poorly understood yet. Herein, we tracked the evolution of phase transitions, in which the destructive volume change and H3 phase formation presented in PC, are effectively suppressed in SC when cycling at a high cut-off voltage of 4.6 V, further clarifying the origin of high-voltage stability in SC cathode. Moreover, SC electrode displayed crack-free morphology, and excellent electrochemical stability during long-term cycling, whereas PC suffered severe capacity and voltage fade because of the spinel-like phase, decoding the failure mechanisms of PC and SC during cycling at high cut-off voltages. This finding provides universal insights into high-voltage stability and failure mechanisms of layered Ni-rich cathode materials.

Triggering oxygen redox activity has been regarded as a promising strategy to boost the output capacity of cathode materials for Li/Na-ion batteries. However, irreversible loss of lattice oxygen aggravates a structural distortion to a spinel phase, which leads to severe voltage decay and capacity degeneration. Herein, via chemical ion exchange procedure, the sodium within the alkali metal layer of a P2-type oxide precursor has been substituted by Li while the transition metal layer can be well preserved, resulting in the formation of a Li-excess O2-type layered oxide cathode, Li0.66[Li0.12Ni0.15Mn0.73]O2. Through systematic in/ex-situ and surface/bulk characterization (hard X-ray absorption spectroscopy, operando Raman/XRD and differential electrochemical mass spectroscopy, etc.), the redox reversibility and structural stability has been comprehensively demonstrated. Moreover, being evolved from the same sodium-based precursor, a similar O2-type compound generated by electrochemical ion exchange procedure presents severely irreversible behavior on both structural and redox processes. These findings elucidated that the chemical ion exchange strategy can be regarded as an efficient way to design high-capacity cathode candidates possessing stable anionic/cationic redox activities and enhanced structural stability.

The Mg battery is an energy storage technology which has garnered significant interest in recent years. Mg batteries incorporating a metal oxide cathode (MOC) are potential candidates to supersede ...

Magnesium batteries have attracted great attention as an alternative to Li-ion batteries but still suffer from limited choice of positive electrode materials. V

The capacity of transition metal oxides as Li-ion battery cathodes is limited by instabilities that arise when high states of charge are achieved. Oxyfluorides with a disordered rock-salt structure have emerged as attractive alternatives, but the role of F in their electrochemical function, particularly when metals reach high formal oxidation states through cationic redox, remains to be ascertained. Using XAS measurements of Mn, O and F, we reveal the existence of Mn-F covalent interactions in Li2MnO2F and Li2Mn2/3Nb1/3O2F. New unoccupied states evolve from both Mn-F and Mn-O interactions when the phases are delithiated. The results challenge the assumption of F as largely a spectator ion, providing instead a nuanced picture of redox compensation in oxyfluorides. They suggest the existence of unique knobs of design of battery cathodes in these chemical spaces, by manipulating the covalent interactions between transition metals and two different anions.

Transition-metal dichalcogenides (TMDCs) such as MoS2 are earth-abundant catalysts that are attractive for many chemical processes, including the carbon dioxide reduction reaction (CO2RR). While many studies have correlated synthetic preparation and architectures with macroscopic electrocatalytic performance, not much is known about the state of MoS2 under functional conditions, particularly its interactions with target molecules like CO2. Here, we combine operando Mo K- and S K-edge X-ray absorption spectroscopy (XAS) with first-principles simulations to track changes in the electronic structure of MoS2 nanosheets during CO2RR. Comparison of the simulated and measured XAS discerned the existence of Mo-CO2 binding in the active state. This state perturbs hybridized Mo 4d-S 3p states and is critically mediated by sulfur vacancies induced electrochemically. The study sheds new light into the underpinnings of the excellent performance of MoS2 in CO2RR. The electronic signatures we reveal could be a screening criterion toward further gains in activity and selectivity of TMDCs in general.

α-V2O5 has been extensively explored as a Mg2+ intercalation host with potential as a battery cathode, offering high theoretical capacities and potentials vs. Mg2+/Mg. However, large voltage hysteresis is observed with Mg insertion and extraction, introducing significant and unacceptable round-trip energy losses with cycling. Conventional interpretations suggest that bulk ion transport of Mg2+ within the cathode particles is the major source of this hysteresis. Herein, we demonstrate that nanosizing α-V2O5 gives a measurable reduction to voltage hysteresis on the first cycle that substantially raises energy efficiency, indicating that mechanical formatting of the α-V2O5 particles contributes to hysteresis. However, no measurable improvement in hysteresis is found in the nanosized α-V2O5 in latter cycles despite the much shorter diffusion lengths, suggesting that other factors aside from Mg transport, such as Mg transfer between the electrolyte and electrode, contribute to this hysteresis. This observation is in sharp contrast to the conventional interpretation of Mg electrochemistry. Therefore, this study uncovers critical fundamental underpinning limiting factors in Mg battery electrochemistry, and constitutes a pivotal step towards a high-voltage, high-capacity electrode material suitable for Mg batteries with high energy density.

The theoretical energy density of lithium–oxygen (Li–O2) batteries is extremely high, although there are many challenges that must be overcome to achieve high energy density in a manufactured cell....

The presence of H2O has been linked to enhancements in the reactivity of cathodes for Mg2+ electrochemistry. If the enhancements were mimicked by nonaqueous solvents, they could enable Mg batteries...

Oxides with the CaFe2O4-type structure have been predicted as being suitable hosts for reactions of intercalation of light cations such as Li and Mg because of their favorable cationic diffusion. A...

Prior calculations have predicted that chalcohalide antiperovskites may exhibit enhanced ionic mobility compared to oxyhalide antiperovskites as solid-state electrolytes. Here, the synthesis of Ag-, Li-, and Na-based chalcohalide antiperovskites is investigated using first-principles calculations and in situ synchrotron X-ray diffraction. These techniques demonstrate that the formation of Ag3SI is facilitated by the adoption of a common body centered cubic packing of S2- and I- in the reactants and products at elevated temperatures, with additional stabilization achieved by the formation of a solid solution of the anions. The absence of these two features appears to hinder the formation of the analogous Li and Na antiperovskites.

Nonaqueous Mg batteries can theoretically reach high energy density with cost-effective materials, yet no such device to date has performance competitive with Li-ion technologies. A major barrier i...

Lattice Mg2+ in a tailored solid solution spinel, MgCrMnO4, is electrochemically utilized at high Mn-redox potentials in a nonaqueous electrolyte. Complementary evidence from experimental and theor...

Metal oxyfluorides are currently attracting much attention for next-generation rechargeable batteries because of their high theoretical capacity and resulting high energy density. Rhombohedral VO2F...

Side reactions involving surface reduction play a critical role in the failure of LiNi0.8Co0.15Al0.05O2 to reach its theoretical capacity as a cathode material for Li-ion batteries. While macroscop...

The use of oxide cathodes in Mg batteries would unlock a potential energy storage system that delivers high energy density. However, poor kinetics of Mg diffusion in known solid oxide lattices stro...

Cathodes based on layered LiMO2 are the limiting components in the path toward Li-ion batteries with energy densities suitable for electric vehicles. Introducing an over-stoichiometry of Li increases storage capacity beyond a conventional mechanism of formal transition metal redox. Yet the role and fate of the oxide ligands in such intriguing additional capacity remain unclear. This reactivity was predicted in Li3Ru5+O4, making it a valuable model system. A comprehensive analysis of the redox activity of both Ru and O under different electrochemical conditions was carried out, and the effect of Li/Ru ordering was evaluated. Li3RuO4 displays highly reversible Li intercalation to Li4RuO4 below 2.5 V vs. Li+/Li0, with conventional reactivity through the formal Ru5+-Ru4+ couple. In turn, it can also undergo anodic Li extraction at 3.9 V, which involves of O states to a much greater extent than Ru. This reaction competes with side processes such as electrolyte decomposition and, to a much lesser extent, oxygen loss. Although the associated capacity is reversible, re-intercalation unlocks a different, conventional pathway also involving the formal Ru5+-Ru4+ couple despite operating above 2.5 V, leading to chemical hysteresis. This new pathway is both chemically and electrochemically reversible in subsequent cycles. This work exemplifies both the challenge of stabilizing highly depleted O states, even with 4d metals, and the ability of solids to access the same redox couple at two very different potential windows depending on the underlying structural changes. It highlights the importance of properly defining the covalency of oxides when defining charge compensation in view of the design of materials with high capacity for Li storage.

In an effort to improve the cycle life and rate capability of olivine LiCoPO4, Cr, Fe, and Si were added to produce nominal Li1.025Co0.84Fe0.10Cr0.05Si0.01(PO4)1.025. This cathode material has an e...

Racemates have recently received attention as nonlinear optical and piezoelectric materials. Here, a machine-learning-assisted composition space approach was applied to synthesize the missing M = Ti, Zr members of the Δ,Λ-[Cu(bpy)2(H2O)]2[MF6]2·3H2O (M = Ti, Zr, Hf; bpy = 2,2'-bipyridine) family (space group: Pna21). In each (CuO, MO2)/bpy/HF(aq) (M = Ti, Zr, Hf) system, the polar noncentrosymmetric racemate (M-NCS) forms in competition with a centrosymmetric one-dimensional chain compound (M-CS) based on alternating Cu(bpy)(H2O)22+ and MF62- basic building units (space groups: Ti-CS (Pnma), Zr-CS (P1), Hf-CS (P2/n)). Machine learning models were trained on reaction parameters to gain unbiased insight into the underlying statistical trends in each composition space. A human-interpretable decision tree shows that phase selection is driven primarily by the bpy:CuO molar ratio for reactions containing Zr or Hf, and predicts that formation of the Ti-NCS compound requires that the amount of HF present be decreased to raise the pH, which we verified experimentally. Predictive leave-one-metal-out (LOO) models further confirm that behavior in the Ti system is distinct from that of the Zr and Hf systems. The chemical origin of this distinction was probed via fluorine K-edge X-ray absorption spectroscopy. Pre-edge features in the F1s X-ray absorption spectra reveal the strong ligand-to-metal π bonding between Ti(3d - t2g) and F(2p) states that distinguishes the TiF62- anion from the ZrF62- and HfF62- anions.

International audience; Water electrolysis is considered as a promising way to store and convert excess renewable energies into hydrogen, which is of high value for many chemical transformation processes such as the Haber-Bosch process. However, to allow for the widespread of the polymer electrolyte membrane water electrolysis (PEMWE) technology, the main challenge lies in the design of robust catalysts for oxygen evolution reaction (OER) under acidic conditions since most of transition metal-based oxides undergo structural degradation under these harsh acidic conditions. To broaden the variety of candidate materials as OER catalysts, a cation-exchange synthetic route was recently explored to reach crystalline pronated iridates with unique structural properties and stability. In this work, a new protonated phase H 3.6 IrO 4 •3.7H 2 O, prepared via Sr 2+ /H + cation exchange at room temperature starting from the parent Ruddlesden-Popper Sr 2 IrO 4 phase, is described. This is the first discovery of crystalline protonated iridate forming from a perovskite-like phase, adopting a layered structure with apex-linked IrO 6 octahedra. Furthermore, H 3.6 IrO 4 •3.7H 2 O is found to possess not only an enhanced specific catalytic activity, superior to that of other perovskite-based iridates, but also a mass activity comparable to that of nanosized IrO x particles, while showing an improved catalytic stability owing to its ability to reversibly exchange protons in acid.

Transition metal dichalcogenides (TMDCs) have garnered much attention recently due to their remarkable performance for different electrochemical systems. In this study, we report on the synthesis a...

To advance current Li rechargeable batteries further, tremendous emphasis has been made on the development of anode materials with higher capacities than the widely commercialized graphite. Some of these anode materials exhibit capacities above the theoretical value predicted based on conventional mechanisms of Li storage, namely insertion, alloying, and conversion. In addition, in contrast to conventional observations of loss upon cycling, the capacity has been found to increase during repeated cycling in a significant number of cases. As the internal environment in the battery is very complicated and continuously changing, these abnormal charge storage behaviors are caused by diverse reactions. In this review, we will introduce our current understanding of reported reactions accounting for the extra capacity. It includes formation/decomposition of electrolyte-derived surface layer, the possibility of additional charge storage at sharp interfaces between electronic and ionic sinks, redox reactions of Li-containing species, unconventional activity of structural defects, and metallic-cluster like Li storage. We will also discuss how the changes in the anode can induce capacity increase upon cycling. With this knowledge, new insights into possible strategies to effectively and sustainably utilize these abnormal charge storage mechanisms to produce vertical leaps in performance of anode materials will be laid out.

Graphite intercalation compounds continue to be central to technologies for electrochemical energy storage from anodes in established Li-ion batteries to cathodes in beyond Li-ion concepts paired w...

International audience