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P3-type K0.6Cr0.6Ti0.4O2 is synthesized via a solid-state method and is tested as a positive electrode for potassium-ion batteries.

Highly concentrated electrolytes (HCEs) have attracted great interest as electrolyte candidates for Li metal batteries because of their functionalities in improving the reversibility and cycling performance of the Li metal negative electrode.

High-capacity electrode materials made of abundant elements are necessary to develop cost-effective energy storage applications.

Domain structure in Li-rich disordered rocksalt-type cathode particles is visualized using X-ray spectroscopic ptychography and clustering analysis.

Lithium-containing metal sulfides, LiMe0.5Ti0.5S2 (Me = Fe2+, Mn2+, and Mg2+), with cation-disordered rocksalt and a cation-ordered layered structure are synthesized and tested as electrode materials for Li battery applications. The disordered rocksalt sulfides show a better electrode performance when compared with materials with the ordered layered structure, which is a clearly different trend from lithium-containing metal oxides. Nearly all Li ions are reversibly extracted with anionic redox for rocksalt Li1–xMn0.5Ti0.5S2. Although electrode reversibility is not high because of a relatively higher solubility in carbonate-based electrolyte solution, cyclability as electrode materials is effectively improved by the use of polymer-based solid electrolyte., This document is the Accepted Manuscript version of a Published Work that appeared in final form in ACS Appled Energy Materials, 2022, 5, 3. Copyright © 2022 American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://pubs.acs.org/articlesonrequest/AOR-WFPXZD5WPBDYVYHRYJFR.

A Li-excess cation-disordered rocksalt (DRS) positive electrode material with Nb/V ions, Li1.25Nb0.25V0.5O2 (LNVO), delivers a high reversible specific capacity of >250 mA h g–1 on the basis of two-electron redox of V3+/V5+. However, the inferior rate performance originating from a character of the disordered structure prevents its use for practical applications. Here, a facile and efficient top-down approach to synthesize nanosized LNVO carbon composited materials has been developed through a combination of ball-milling and subsequent heat-treating steps. The markedly improved rate capability is achieved by highly graphitic carbon coating with superior conductivity derived from a precursor with a perylene core. The growth of particle sizes of LNVO is effectively suppressed by uniform mixing of the precursor by optimized milling conditions. The optimized nanosized sample with shorter Li ion migration paths shows excellent rate capability for the rocksalt oxide. Moreover, superior capacity retention for continuous 100 cycles is also achieved. Furthermore, by lowering the Li ion migration barrier at elevated temperatures, a larger reversible specific capacity of 300 mA h g–1, which nearly corresponds to its theoretical specific capacity, is obtained, coupled with further improved rate capability because of facile conduction for Li ions in oxides and electrolyte. This finding opens the possibility to develop high-performance electrode materials with a cation-DRS structure for practical battery applications., This document is the Accepted Manuscript version of a Published Work that appeared in final form in Chemistry of Materials 2022, 34, 4. Copyright © 2022 American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://pubs.acs.org/articlesonrequest/AOR-W3C98JNBHG3HP2UVNPQ4.

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.

Ni-enriched layered materials are utilized as positive electrode materials of high-energy Li-ion batteries. Because electrode reversibility is gradually lost for stoichiometric LiNiO2 after continuous cycles, Ni ions are partially substituted by other metal ions (Co, Mn, Al etc.). However, the origin of deterioration in stoichiometric LiNiO2 is still not fully understand yet. Moreover, the loss of capacities is observed only in the high voltage region (>4.1 V), which is obviously different from the failure mode observed in other electrode materials. Here, we report for the first time the origin of deterioration, which is revealed by an in situ X-ray diffraction study. For fully charged NiO2, Ni ions migrate from original octahedral sites in NiO2 slabs to face-sharing tetrahedral sites in Li layers, by which the O3 to O1 phase transition is suppresed. Note that Ni migration is a reversible process, and the Ni ions migrate back to the original octahedral sites on discharge. However, after continuous cycles, the reversibility of Ni migration is gradually lost, and Ni ions are partially left at the tetrahedral sites in Li layers. Electrode kinetics are also deteriorated because of the Ni occupation in Li layers, and the accumulation of Ni ions at tetrahedral sites results in the loss of reversible capacities in the high voltage region. This finding opens a new way to design high-capacity Ni-enriched electrode materials, leading to the development of high-energy Li-ion batteries.

Na_(0.67)Cr_(0.33)Mg_(0.17)Ti_(0.5)O_2 with a P2-type layered structure has been synthesized and examined as a negative electrode material for rechargeable sodium batteries. The layered oxide delivers a reversible capacity of >90 mA h g^(-1), which corresponds to >95% of the theoretical capacity with excellent cyclability for >450 cycles.

A binary system of Li2TiO3–LiMnO2 is systematically examined by joint experimental and theoretical studies as electrode materials for Li storage applications. Increase in a fraction of Li2TiO3 effectively activates anionic redox, and thus holes are reversibly formed on oxygen by electrochemical oxidation. Such holes are energetically stabilized through π-type interaction with Mn t2g orbital as suggested by theoretical calculation. However, excess enrichment of Li2TiO3 fractions in this binary system results in the oxygen loss as an irreversible process on delithiation because of a non-bonding character for Ti–O bonds coupled with the formation of O–O dimers, which are chemically and electrochemically unstable species. Additionally, detailed electrochemical study clearly shows that Li migration kinetics is relatively slow, presumably coupled with low electronic conductivity. Nevertheless, nanosizing of primary particles is an effective strategy to overcome this limitation. The nanosized sample prepared by mechanical milling delivers a large reversible capacity, ∼300 mA h g−1, even at room temperature and shows much improved capacity retention. Formation and stabilization of holes for the nanosized sample are also directly evidenced by soft X-ray absorption spectroscopy. From these results, factors affecting the reversibility of anionic redox as emerging new chemistry and its possibility for energy storage applications are discussed in more details.

Hard carbon possesses the ability to store Li, Na, and K ions between stacked sp2 carbon layers and voids (micropores). We have explored hard carbon as a candidate for negative electrode materials ...

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...

A titanium-substituted lithium-excess molybdenum oxyfluoride, Li2.1–yTi0.2Mo0.7O2F, is synthesized by mechanical milling and tested as a positive electrode material in a conventional carbonate-based electrolyte or concentrated electrolyte. Reversibility as the electrode material is significantly improved by suppression of dissolution of the molybdenum oxyfluoride on electrochemical cycles. Li2.1–yTi0.2Mo0.7O2F delivers a reversible capacity of 265 mA h g–1 after 30 cycles at a rate of 50 mA g–1 with concentrated electrolyte. This finding contributes to the development of high-energy and long-cycle-life rechargeable lithium batteries with lithium-excess metal oxyfluorides in the future.

The incompatibility between Li+-intercalated electrodes and water limits the practical feasibility of aqueous lithium-ion batteries (LIBs), which are economical and environmentally benign energy storage systems. Tremendous amounts of salts dissolved in water (water-in-salt) have been utilized to mitigate the access of water to the electrode/electrolyte interface and to extend the electrochemical potential window of aqueous LIBs. However, this approach has low viability owing to the expense of the salts. Here, we show that kosmotropic anions with moderate concentrations (0.5 ~ 3 mol kg− 1) protect the LiCoO2 electrode by harnessing water molecules. The sulfates of kosmotropic anions develop rigid water-solvation shells and also form ion pairs with Li+. All-atomic-level multiscale simulation revealed that sulfates tied with Li+ and the water shell are highly concentrated at the interface, thus decreasing the density of free water. The suppressed water activity explains the superior cell performance achieved with 0.5 mol kg− 1 sulfate relative to that in cells with 1 mol kg− 1 of chaotropic anions such as nitrate, perchlorate, and bis(trifluoromethylsulfonyl)imide. The formation of a liquid-phase protective layer is a new concept for developing stable aqueous batteries without the requirement for a solid-state electrolyte or an artificial protective layer on the electrode.

Na0.67Cr0.33Mg0.17Ti0.5O2 with a P2-type layered structure has been synthesized and examined as a negative electrode material for rechargeable sodium batteries. The layered oxide delivers a reversible capacity of90 mA h g-1, which corresponds to95% of the theoretical capacity with excellent cyclability for450 cycles.

Delivering inherently stable lithium-ion batteries is a key challenge. Electrochemical lithium insertion and extraction often severely alters the electrode crystal chemistry, and this contributes to degradation with electrochemical cycling. Moreover, electrodes do not act in isolation, and this can be difficult to manage, especially in all-solid-state batteries. Therefore, discovering materials that can reversibly insert and extract large quantities of the charge carrier (Li+), that is, high capacity, with inherent stability during electrochemical cycles is necessary. Here lithium-excess vanadium oxides with a disordered rocksalt structure are examined as high-capacity and long-life positive electrode materials. Nanosized Li8/7Ti2/7V4/7O2 in optimized liquid electrolytes deliver a large reversible capacity of over 300 mAh g−1 with two-electron V3+/V5+ cationic redox, reaching 750 Wh kg−1 versus metallic lithium. Critically, highly reversible Li storage and no capacity fading for 400 cycles were observed in all-solid-state batteries with a sulfide-based solid electrolyte. Operando synchrotron X-ray diffraction combined with high-precision dilatometry reveals excellent reversibility and a near dimensionally invariable character during electrochemical cycling, which is associated with reversible vanadium migration on lithiation and delithiation. This work demonstrates an example of an electrode/electrolyte couple that produces high-capacity and long-life batteries enabled by multi-electron transition metal redox with a structure that is near invariant during cycling.

Stoichiometric LiMnO2 and NaMnO2 with a cation-disordered rocksalt-type structure as metastable polymorphs were successfully prepared by mechanical milling. Although cation-disordered rocksalt phases with a stoichiometric composition (Li : Mn molar ratio = 1 : 1) are expected to be electrochemically less active, both samples show superior performance as electrode materials when compared with thermodynamically stable layered phases in Li/Na cells. Both metastable samples deliver large reversible capacities, which correspond to >80% of their theoretical capacities, with relatively small polarization on the basis of reversible Mn3+/Mn4+ redox. Moreover, for rocksalt LiMnO2, the phase transition into a spinel phase is effectively suppressed compared with a thermodynamically stable phase. The electrode reversibility of NaMnO2 is also drastically improved by the use of the metastable phase with good capacity retention. Metastable phases with unique nanostructures open a new path for the design of advanced electrode materials with high energy density, and thus a broad impact is anticipated for rechargeable Li/Na battery applications.

We have studied a new electrolyte additive, 1,1-diphenylethane (DPE), to LiCoO2/graphite cells to reduce capacity loss during high temperature storage. It is demonstrated to be effective to reduce polarization after storage at 60 °C for one month in charged state. In half-cell tests, a LiCoO2/Li cell with DPE additive in electrolyte shows less capacity loss than that without DPE, while no significant difference is observed between DPE-added and DPE-free graphite/Li half cells. Scanning electron microscopy, X-ray diffraction, electrochemical impedance spectroscopy, time of flight-secondary ion mass spectroscopy, and hard X-ray photoelectron spectroscopy measurements are applied to elucidate the mechanism how DPE suppresses the increase in electrode resistance and polarization during the high temperature storage. All the results consistently show that less amount of surface layer is formed by electrolyte decomposition on LiCoO2 electrode surface in DPE-added electrolyte than the DPE-free one, leading to reduction of the electrode resistance and polarization.

Lithium-ion batteries provide the development of a clean and sustainable society based on renewable energy resources. To further enhance energy density and reduce the cost of batteries, innovations on electrode materials and high-performance nickel-/cobalt-free materials are necessary. In this review, lithium-excess manganese-based electrode materials with layered/rock salt oxides/oxyfluorides are emphasized because of their potential ability to be utilized as advanced and low-cost lithium-ion batteries in the near future. For these emerging electrode materials, higher energy density is realized, compared with traditional layered materials based on nickel/cobalt ions, relying on anionic and/or cationic redox as multi-electron reactions. Although, currently, anionic redox suffers from degradation of reversibility on continuous cycles, significant progress on theoretical understanding and material design concepts has been made in the past several years. Recently, as alternatives to traditional layered materials, many disordered rock salt oxides, including metastable and nanosized oxyfluorides, have been also found as a new class of high-capacity electrode materials with anionic/cationic redox. In the later part, these new trends for the material design are also extended to the development of electrode materials for sodium-ion batteries. By reviewing the fundamental and recent research progress in metal oxide/oxyfluoride electrodes, a valuable guide for materials scientists in the field of batteries is provided to accelerate the industrial development of high-performance nickel-/cobalt-free electrode materials.

The effect of nanosizing on the sodium storage performance in NaCrO2 is systematically examined. Cation-disordered rock-salt-type and nanosized NaCrO2 is prepared by mechanical milling, and layered O3-type and nanosized NaCrO2 is prepared by heat treatment of the rock-salt phase. The observation by high-resolution transmission electron microscopy reveals that secondary particles consist of highly crystalline and nanosized NaCrO2 primary particles with enriched grain boundaries. Such morphological features influence the voltage profiles in sodium cells, leading to an S-shaped profile with a single-phase reaction even for layered NaCrO2, in which a biphasic reaction dominates because of a large repulsive interaction between Na ions. Moreover, the O3–P3 phase transition is suppressed for the heat-treated sample with the presence of enriched grain boundaries. The suppression of the phase transition is proposed to be due to the cancellation of CrO2 layers gliding for the incoherently aligned grain boundaries. ...

A binary system of LiMoO 2 – x LiF (0 ≤ x ≤ 2), Li 1+ x MoO 2 F x , is systematically studied as potential positive electrode materials for rechargeable Li batteries. Single phase and nanosized samples on this binary system are successfully prepared by using a mechanical milling route. Crystal structures and Li storage properties on the binary system are also examined. Li 2 MoO 2 F ( x = 1), which is classified as a cation-/anion-disordered rocksalt-type structure and is a thermodynamically metastable phase, delivers a large reversible capacity of over 300 mAh g −1 in Li cells with good reversibility. Highly reversible Li storage is realized for Li 2 MoO 2 F consisting of nanosized particles based on Mo 3+ /Mo 5+ two-electron redox as evidenced by ex-situ X-ray absorption spectroscopy coupled with ex-situ X-ray diffractometry. Moreover, the presence of the most electronegative element in the framework structure effectively increases the electrode potential of Mo redox through an inductive effect. From these results, potential of nanosized lithium molybdenum oxyfluorides for high-capacity positive electrode materials of rechargeable Li batteries are discussed.

Electrochemical performance of the red phosphorus electrode was examined in ionic-liquid electrolyte, 0.25 mol dm −3 sodium bisfluorosulfonylamide (NaFSA) dissolved N-methyl-N-propylpyridinium-bisfluorosulfonylamide (MPPFSA), at room temperature. We compared its electrochemical performance to conventional EC/PC/DEC, EC/DEC, and PC solutions containing 1 mol dm −3 NaPF 6 . The electrode in NaFSA/MPPFSA demonstrated a reversible capacity of 1480 mAh g −1 and excellent capacity retention of 93% over 80 cycles, which is much better than those in the conventional electrolytes. The difference in capacity retention for the electrolytes correlates to the different solid electrolyte interphase (SEI) layer formed on the phosphorus electrode. To understand the SEI formation in NaFSA/MPPFSA and its evolution during cycling, we investigate the surface layer of the red phosphorus electrodes with hard X-ray photoelectron spectroscopy (HAXPES) and time-of-flight secondary ion mass spectrometry (TOF-SIMS). A detailed analysis of HAXPES spectra demonstrates that SEI layer consists of major inorganic and minor organic species, originating from decomposition of MPP + and FSA − . Homogenous surface layer is formed during the first cycle in NaFSA/MPPFSA while in alkyl carbonate ester electrolytes, continuous growth of surface film up to the 20 th cycle is observed. Possibility of red phosphorous electrode for battery applications with pure ionic liquid is discussed.