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Cost‐effective Fe‐based cathode materials have attracted significant attention. Recently, antifluorite‐type Li5FeO4 has been investigated as a high‐capacity cathode material owing to its high lithium content and solid‐state oxygen redox reactions. However, its reversible capacity is restricted to transition‐metal redox reactions because of its irreversible structural transformation and oxygen evolution. This study demonstrates the reversible oxygen redox reaction in metastable cubic antifluorite Li5FeO4 obtained by mechanochemical treatment. It exhibits a reversible capacity of more than 300 mAh g‐1, corresponding to an approximately 1.7‐electron reaction, without oxygen gas evolution. Combined analyses of X‐ray absorption spectroscopy (XAS) and theoretical calculations reveal that both Fe3+/Fe4+ and O2‐/O22‐ redox reactions proceed under semi‐coherent structural transformations between antifluorite and rocksalt, which differs from the known orthorhombic Li5FeO4 phase. Although the cyclability of oxygen redox is poor, its solid solution with Co2+ enhances cyclability by suppressing oxygen evolution. Tuning the structural symmetry and transition‐metal content can overcome the reversible capacity limit of antifluorite cathode materials, which is useful for the development of high‐energy cathode materials by the effective utilization of solid‐state oxygen redox reactions. [ABSTRACT FROM AUTHOR]

While organic batteries have attracted great attention due to their high theoretical capacities, high‐voltage organic active materials (> 4 V vs Li/Li+) remain unexplored. Here, density functional theory calculations are combined with cyclic voltammetry measurements to investigate the electrochemistry of croconic acid (CA) for use as a lithium‐ion battery cathode material in both dimethyl sulfoxide and γ‐butyrolactone (GBL) electrolytes. DFT calculations demonstrate that CA dilitium salt (CA–Li2) has two enolate groups that undergo redox reactions above 4.0 V and a material‐level theoretical energy density of 1949 Wh kg–1 for storing four lithium ions in GBL—exceeding the value of both conventional inorganic and known organic cathode materials. Cyclic‐voltammetry measurements reveal a highly reversible redox reaction by the enolate group at ≈4 V in both electrolytes. Battery‐performance tests of CA as lithium‐ion battery cathode in GBL show two discharge voltage plateaus at 3.9 and 3.1 V, and a discharge capacity of 102.2 mAh g–1 with no capacity loss after five cycles. With the higher discharge voltages compared to the known, state‐of‐the‐art organic small molecules, CA promises to be a prime cathode‐material candidate for future high‐energy‐density lithium‐ion organic batteries. [ABSTRACT FROM AUTHOR]

Atomic-resolution imaging of the crystal defects of cathode materials is crucial to understand their formation and the correlation between the structure, electrical properties, and electrode performance in rechargeable batteries. The polytype, a stable form of varied crystal structure with uniform chemical composition, holds promise to engineer electronic band structure in nanoscale homojunctions.- Analyzing the exact sites of atoms and the chemistry of the boundary in polytypes would advance our understanding of their formation and properties. Herein, the polytype and stacking faults in the lithium cobalt silicates are observed directly by aberration-corrected scanning transmission electron microscopy. The atomic-scale imaging allows clarification that the polytype is formed by stacking of two different close-packed crystal planes in three-dimensional space. The formation of the polytype was induced by Li-Co cation exchange, the transformation of one phase to the other, and their stacking. This finding provides insight into intrinsic structural defects in an important Li2CoSiO4 Li-ion battery cathode. [ABSTRACT FROM AUTHOR]

Rechargeable Mg-ion batteries have gained significant attention as promising alternatives to Li-ion batteries. Owing to its high theoretical energy density and relatively high Mg-ion diffusivity, spinel oxide MgMn 2 O 4 is a viable candidate as a cathode material; however, its poor rate capability limits its applicability. Decreasing the particle size can effectively address this problem by enhancing Mg-ion diffusion. In this paper, we demonstrate the conventional solvothermal synthesis of MgMn 2 O 4 spinel nanoparticles. Solvothermal process is one of the most fundamental methods for nanoparticle synthesis because of its simple and flexible synthetic conditions. In the alcohol solvothermal conditions, spinel type MgMn 2 O 4 nanoparticles of approximately 10–15 nm are successfully synthesized using amorphous MnO 2 as a precursor. We note that controlling Mg2+ solvation and oxidation/reduction conditions in the reaction solution is crucial for the effective intercalation of Mg2+ into the MnO 6 octahedral framework. Although the obtained MgMn 2 O 4 nanoparticles aggregate to form submicron secondary particles, the aggregation can be suppressed by compositing them with the carbon nanotubes dispersed in the reaction solution. The composite exhibits a discharge capacity of 60 mAh g−1 with maintaining 80% of capacity retention after the 10th cycle. Image 1 • MgMn 2 O 4 spinel nanoparticles were selectively synthesized by reductive solvothermal process. • Reductive reaction and dehydrated solvation of Mg2+ are preferable for wet-process synthesis. • MgMn 2 O 4 -carbon nanotube composite was obtained by a one-pot solvothermal route. • The composite exhibited improved cathode performances at room temperature. [ABSTRACT FROM AUTHOR]

[Display omitted] • Sodium croconate composite cathodes were evaluated for sodium-ion battery. • The developed organic cathode exhibited a 3.5 V-class high-voltage redox activity. • Full cell with the sodium croconate cathode and hard carbon anode was fabricated. • Completely rare-metal-free battery exhibited high energy density of 430 Wh kg−1. Sodium-ion batteries (SIBs) based on organic cathode materials have received considerable attention owing to high theoretical capacities, cost-effectiveness, and raw material abundance. However, high-voltage organic cathodes have been rarely investigated for SIBs mainly due to their electrical insulation and dissolution in electrolytes. In this study, sodium croconate (C 5 O 5 Na 2) is utilized as a high-voltage cathode material for SIBs, designing an interface using a functionalized multi-walled carbon nanotube (MWCNT). The composite C 5 O 5 Na 2 cathode with carboxylic-acid-functionalized-(COOH–) MWCNT exhibits a 3.5 V-class high-voltage redox activity with a cycle performance higher than that of non-functionalized MWCNT/C 5 O 5 Na 2 composite cathodes; the capacity retention ratio is improved from 0 % to 34 % after 30 cycles at 0.1C. Raman, X-ray photoelectron spectroscopy, and solid-state nuclear magnetic resonance reveal the formation of hydrogen bonding between COOH groups on MWCNT and carbonyl groups in C 5 O 5 Na 2 molecules; leading to suppression of organic molecules and improvement on the cycle performance. A full cell assembled with the C 5 O 5 Na 2 /COOH–MWCNT cathode and a hard carbon anode also shows a high-voltage redox plateau at around 3.5 V and a 1st discharge capacity of 123 mAh g−1 at 1C. These results suggest the feasibility of developing a high-energy-density storage system using completely common-metal components. [ABSTRACT FROM AUTHOR]

Structural studies of high voltage cathode materials are necessary to understand their chemistry to improve the electrochemical performance for applications in lithium ion batteries. LiNiPO4 nanorods and nanoplates are synthesized via a one pot synthesis using supercritical fluid process at 450 oC for 10 min. The X-ray diffraction (XRD) analysis confirmed that LiNiPO4 phase is well crystallized, phase purity supported by energy dispersive spectroscopy (EDS) and elemental mapping by scanning electron transmission electron microscopy (STEM). For the first time, we have carried out direct visualization of atom-by-atom structural observation of LiNiPO4 nanomaterials using high-angle annular dark-field (HAADF) and annular bright-field (ABF) scanning transmission electron microscopy (STEM) analysis. The Rietveld refinement analysis was performed to find out the percentage of antisite defects presents in LiNiPO4 nanoplates and about 11% of antisite defects were found. Here, we provide the direct evidence for the presence of Ni atoms in Li sites and Li in Ni sites as an antisite defects are provided for understanding of electrochemical behavior of high voltage Li ion battery cathode materials. [ABSTRACT FROM AUTHOR]

Abstract: A cheap and rapid supercritical hydrothermal method has been adopted for the synthesis of Li2FeSiO4 cathode materials for the application in lithium ion battery. The as-synthesized Li2FeSiO4 particles at 380°C exhibited rod like morphology with 20–80nm in diameter and 500nm–1μm in length characterized by transmission electron microscopy (TEM). The Li2FeSiO4 material is systematically characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermo gravimetric analysis (TG), scanning transmission electron microscopy (STEM) and energy dispersive X-ray (EDX). The electrochemical measurements were carried out after coating of Li2FeSiO4 particles with different weight percentage of conductive carbon. The discharge capacity of as-synthesized rod like Li2FeSiO4 with 30wt% conductive carbon coating exhibited 177mAhg−1 for the first cycle, which is more than that of as-synthesized and 20wt% conductive carbon coated rod like Li2FeSiO4 particles. The obtained discharge capacity is the highest for this material without high temperature heat treatment, which indicating that rod like morphology with diameter 20–80nm could be more active during electrochemical reactions. [Copyright &y& Elsevier]

Abstract: Solid-state cells are one of the strongest candidate designs for utilisation of renewable high-capacity organic cathode materials. Following our previous work on tetracyanoquinodimethane, further high-capacity quinonic compounds, namely dichlorodicyanobenzoquinone, tetrahydroxybenzoquinone and dihydroxybenzoquinone were investigated. Cell cycling experiments indicated that these compounds undergo reversible redox reaction with significantly less cyclic capacity decay. 3.4 V of cell voltage was attainable from DDQ cells and capacities exceeding 250 mAh g−1 were obtained from THBQ and DHBQ. These results reassure that by adopting an appropriate battery design, cycleability of organic cathodes can be drastically improved and they can be exploited as low-cost environmentally friendly high energy-density cathode materials. [Copyright &y& Elsevier]

We studied the electronic and structural properties of electron-deficient anthraquinone (AQ) derivatives, Me 4 N 4 AQ and TCNAQ, and investigated their charge-discharge properties in lithium ion batteries along with those of AQ. Cyclic voltammogram, X-ray structure analysis and theoretical calculations revealed that these three acceptors have different features, such as different electron-accepting properties with different reduction processes and lithium coordination abilities, and different packing arrangements with different intermolecular interactions. These differences greatly affect the charge-discharge properties of lithium ion batteries that use these compounds as cathode materials. Among these compounds, Me 4 N 4 AQ showed a high charge/discharge voltage (2.9–2.5 V) with high cyclability (>65% of the theoretical capacity after 30 cycles; no decrease after 15 cycles). These results provide insight into more in-depth design principles for lithium ion batteries using AQ derivatives as cathodic materials. [ABSTRACT FROM AUTHOR]

Soft X-ray absorption spectroscopic studies are carried out to clarify the charge/discharge reaction mechanism of Co-doped Li 2 O (CDL, Co/Li = 0.1 molar ratio) as a cathode material for a new rechargeable lithium-peroxide battery. Upon charging CDL in an aprotic electrolyte, a drastic change can be seen in the O K-edge spectra, with a new, strong peak assignable to σ*(O–O) of peroxide at photon energy of 531.0 eV. This peak is reduced during subsequent discharging, causing the spectrum to essentially return to that of pristine CDL recorded in total fluorescence yield mode. The Co L 2,3 -edge spectra do not show a remarkable change during charging, with the exception of the disappearance of a Co 2+ shoulder peak. The spectrum of charged CDL is in reasonable agreement with the calculated spectrum, assuming that the fraction of Co 3+ – L (where L indicates a hole state in the oxygen 2 p band) is dominant in the electronic configuration of the ground state. This suggests that, to a certain extent, a redox reaction involving a ligand hole state (Co 3+ – L ) participates in generation of the capacity. [ABSTRACT FROM AUTHOR]

Abstract: Li2CoPO4F cathode materials have been synthesized by a two-step method combining a sol-gel route and solid state reaction. X-ray diffraction (XRD) analysis confirmed that the Li2CoPO4F was well-crystallized in orthorhombic crystal structure with Pnma space group. From the high resolution transmission electron microscopy (HRTEM) image; the lattice fringes of {001} and {100} are well-resolved. HRTEM image and selected area electron diffraction (SAED) pattern reveal the highly crystalline nature of Li2CoPO4F having an ordered orthorhombic crystal structure. The Co atoms chains of Li2CoPO4F have been observed using high angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). The Raman and Fourier transform infrared spectroscopy (FTIR) spectra indicate the symmetry and stability of the Li2CoPO4F structure. The Li2CoPO4F cathode materials delivered an initial discharge capacity of 91 mAhg−1 at C/10 rate with good cyclic performance. The discharge profile of Li2CoPO4F shows a plateau at 5.0V; revealing its importance as potentially high-voltage cathode. [Copyright &y& Elsevier]

Abstract: The fabrication of single crystalline Li0.44MnO2 nanowires for the positive electrode of lithium ion battery is reported. The single crystalline Li0.44MnO2 nanowires are obtained by lithium exchange reaction of Na0.44MnO2 nanowires with high aspect ratio. The Li0.44MnO2 nanowires indicate both the large specific capacity of around 250mAhg−1 (1.5–4.5V vs. Li/Li+) and the good high current density property for the positive electrode of lithium ion battery. [Copyright &y& Elsevier]

Abstract: We demonstrate a rapid and one-pot solvothermal synthesis of LiFePO4 hierarchical nanorods and flowers like microstructures in a short reaction time (4–10min) at temperature as low as 300–400°C, without any high temperature post-annealing. The ethylene glycol was used as a solvent with hexane and oleic acid as co-solvent and surfactant, respectively. Addition of the co-solvent and/or surfactant played a key role in controlling the morphology and microstructures of the LiFePO4 nanocrystals. The EG and oleic acid were acted as the size and morphology controlling agents and carbon source when annealed at 600°C. Sample exhibited about 90% specific capacity at 0.5°C and showed good cyclic performance. The high-resolution TEM image revealed that these nanorods were self-assembled to form flower like microstructure in presence of oleic acid during the synthesis. [Copyright &y& Elsevier]

• Al-substituted MgMn 2 O 4 nanoparticles are synthesized by a sol-gel method. • MgMn 2- x Al x O 4 has both tetragonal and cubic spinel phases. • The fraction of cubic spinel phase tends to increase with the Al ratio. • MgMn 2- x Al x O 4 exhibits higher discharge capacity than normal MgMn 2 O 4. • The increase in cubic phase fraction reduces structural change during discharging. [Display omitted] Magnesium rechargeable batteries using Mg-metal anodes are promising post-lithium-ion batteries. MgMn 2 O 4 is a strong candidate cathode material owing to its high energy density and relatively high Mg2+-ion diffusivity. However, while pristine MgMn 2 O 4 forms a tetragonal spinel structure (I 4 1 / amd) owing to the Jahn–Teller effect of Mn3+, it adopts a cubic structure in the charged/discharged state. This results in a structural change from tetragonal to cubic during charge/discharge cycling, leading to poor battery performance and reversibility. To improve the cathode performance, we prepared Al-substituted MgMn 2− x Al x O 4 spinel (x = 0, 0.1, 0.2, 0.5) to suppress the Jahn–Teller distortion. The obtained MgMn 2− x Al x O 4 spinel is a two-phase crystal with coexisting tetragonal and cubic spinel structures, whereby the fraction of cubic phase tends to increase with the Al ratio. The Al-substituted spinels exhibit superior discharge capacities to that of MgMn 2 O 4. The increase in cubic spinel phase fraction by Al-substitution and the reduced structural change during discharging will aid the development of superior cathodes for magnesium batteries. [ABSTRACT FROM AUTHOR]

• Nb 2 O 5 samples were prepared by sol-gel based methods and by rapid heat-treatment. • Au on pseudohexagonal (TT-) Nb 2 O 5 showed high catalytic activity for CO oxidation. • Au/TT-Nb 2 O 5 exhibited high electrochemical properties as cathode of Li-ion batteries. We prepared a series of Nb 2 O 5 polymorphs by the sol-gel method and the sol-gel hydrothermal method. Gold nanoparticles supported on Nb 2 O 5 were prepared by solid grinding method. Au on pseudohexagonal (TT-phase) Nb 2 O 5 containing an amorphous phase exhibited higher catalytic activity for CO oxidation than did other Au/Nb 2 O 5 polymorphs. For the electrochemical properties for cathode materials of Li-ion batteries, Nb 2 O 5 (TT) exhibited high capacity of 208 mA h g-1, and the deposition of Au onto Nb 2 O 5 (TT) improved the capacity to 232 mA h g-1. Capacity and CO oxidation activity were related; the higher the catalytic activity Au/Nb 2 O 5 shows, the higher is the discharging capacity. From the characterization results, Nb 2 O 5 (TT) contains oxygen vacancies (Nb4+ sites), and the oxygen vacancies of Nb 2 O 5 (TT) would play an important role for CO oxidation and the performance for Li-ion batteries. [ABSTRACT FROM AUTHOR]

Lithium-ion battery that consists of a cathode made of (Mo 3 S 11) n polymer and an anode of Li metal exhibits a high gravimetric-capacity, 673.3 mAh g−1. A flexible structure of the (Mo 3 S 11) n polymer enables consecutive redox reactions of the S 2 2− dimer and the Mo atoms. According to X-ray absorption near-edge spectroscopy, X-ray photoelectron spectroscopy and Raman spectroscopy, the chemical bonds of Mo–S and S–S in the polymer elongate by accepting electrons up to 16, while the Mo–Mo bond does not change much during the redox reactions. Although the polymer cathode is put in a solid-state electrolyte, the S 2 2− dimer that is redoxed by the reaction of S 2 2− + 2e− → 2S2− forms Li–S–Li bonds, which is an origin of the high capacity of the battery. The redox reactions in the (Li x Mo 3 S 11) n polymer cathode is theoretically confirmed by first principles calculation. Image 1 [ABSTRACT FROM AUTHOR]