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Abstract: Understanding the redox behavior and structural stability of aliovalent substituents in ionic conductors is critical, as their variable oxidation states can inadvertently introduce electronic conductivity and alter transport mechanisms under different atmospheric conditions. Here, we report the atmosphere-dependent redox behavior and local coordination of Mo in LaNb0.9Mo0.1O4.05, focusing on its influence on phase transition and transport properties, where the as-sintered LaNb0.9Mo0.1O4.05 was systematically annealed under pure O2, pure N2, vacuum (∼1.6 × 10–8 mbar), and 5% H2/N2 at 800 °C for different dwell times. Electron paramagnetic resonance (EPR) spectroscopy results demonstrate the emergence of Mo5+ under 5% H2/N2. In situ X-ray absorption near edge structure (XANES) measurements reveal the reversible redox behavior of Mo, where Mo5+ formed under 5% H2/N2 reoxidizes to Mo6+ upon exposure to static air, while complementary in situ extended X-ray absorption fine structure (EXAFS) analysis shows that the Nb coordination environment also transitions from prototypical LaNbO4 structure under reducing conditions back to the Mo-substituted LaNbO4 structure upon reoxidation. This change of the oxidation states of Mo could correspondingly alter the band structure of the sample, which further enhances charge transport: the sample annealed in 5% H2/N2 for 24 h exhibits a reduced activation energy and increased electronic conductivity. These results highlight a strong coupling among substituent redox flexibility, local structure, and transport properties, providing an understanding of tailoring the properties of ionic conductors through controlled redox environments.

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Abstract: Commercial Li-ion batteries have been optimized to operate in temperate environments. While moderately high or low temperatures are known to reduce battery performance and safety, the effect of passive exposure to more extreme low temperatures remains largely unexplored. In this work, the effect of thermally cycling a Li-ion battery at a controlled rate between room temperature and cryogenic levels (83 K) was characterized using in situ transient grating spectroscopy. Our results show that the acoustic pulses generated by transient grating spectroscopy travel within the porous composite graphite electrode and their time-of-flight is sensitive to changes in state of charge as well as temperature. At room temperature, an increase in time-of-flight was observed when the state of charge of the composite graphite electrode was increased which is attributed to the volume expansion of the electrode. During controlled-rate cooling, a decrease in time-of-flight was observed for cells at different states of charge that is primarily ascribed to an increase in the effective Young’s modulus of the porous composite graphite electrode. This claim was validated with variable-temperature, synchrotron X-ray diffraction on ex situ graphite electrode samples at different states of charge where minimal thermal volume contraction (<1%) of the graphite active material at different degrees of lithiation was observed during cooling to cryogenic temperatures. Upon subsequent controlled-rate warming, time-of-flight values for cells at different states of charge returned to their original values, which suggests that passive exposure to extreme low temperatures induces reversible thermomechanical changes.

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Abstract: Increasing use of lithium-ion batteries (LIBs) urges for efficient recycling strategies for their components. Direct recycling methods for cathode materials, based on repairing the structure of the degraded cathode particles without destroying the bulk phase, are promising energy-saving alternatives to traditional metallurgy processes that involve several steps and use large volumes of chemicals causing secondary pollution. Herein, we report a novel and scalable method for the direct electrochemical recycling of spent lithium iron phosphate (LFP) powder in a flow cell via redox mediation. In this method, pellets of spent LFP powder (S-LFP) placed in a tank are directly reduced and relithiated by a redox mediator dissolved in a Li-containing aqueous electrolyte, pumped from an electrochemical cell stack to the relithiation tank. Redox mediators transport charge to the S-LFP pellets from the electrochemical cell, where Li4Fe(CN)6 is oxidized and Li ions are supplied from a Li4Fe(CN)6-containing counter compartment through an ion-selective membrane. The consumption of the regenerating redox mediator solution is minimal via a closed-loop electrochemical regeneration reaction. Successful S-LFP regeneration using two redox mediators, with different energy demand processes, is confirmed by structural and electrochemical characterization.

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Abstract: This study investigates the layered oxide cathode with NMC-type LiNixMnyCozO2 as the alternative cathode material for lithium ion batteries. This material has attracted the researcher’s interest as alternative cathode material due to its low cost and less toxicity as compared to the most widely commercialised lithium cobalt oxide (LCO). Lithium nickel manganese cobalt oxide (often abbreviated as NMC) is a type of cathode material used in lithium-ion batteries. It's a popular choice because it offers a balance of high energy density, good cycling stability and relatively low cost compared to other cathode materials. In this study we investigate the stability properties of Ni0.3Mn0.5Co0.2CO3 and Ni0.3Mn0.5Co0.2O2, respectively. In particular, we focus on the manganese rich compositions and minor amounts of nickel and cobalt. We further doped both system (Ni0.3Mn0.5Co0.2CO3 and Ni0.3Mn0.5Co0.2O2) with fluorine, titanium, niobium and chromium to check if their contributions could improve or disprove the behaviour of Ni0.3Mn0.5Co0.2CO3 and Ni0.3Mn0.5Co0.2O2 materials. Firstly, the structural, electronic, mechanical and vibrational properties of Ni0.3Mn0.5Co0.2CO3, Ni0.3Mn0.5Co0.2O2 and their doped systems have been calculated using the density functional theory employing the pseudo-potential plane-wave approach within the local gradient approximation with the Hubbard parameter U for strongly correlated transition metals. The structural property calculations included the equilibrium lattice parameters, density and energy of formations while electronic properties included the partial density of states (PDOS), total density of states (TDOS) and band structures for all the systems. Furthermore, mechanical properties investigated the elastic constants, Pugh ratio and anisotropy while vibrational properties investigates the phonon dispersion curves for Ni0.3Mn0.5Co0.2CO3, Ni0.3Mn0.5Co0.2O2 and their doped systems. The calculated lattice parameters and energy of formation could be used for benchmarking in the future since no similar work was found in literature for comparison. Moreover, the calculated energy of formations revealed the relatively low and negative values for all the systems, suggesting thermodynamic stability. With the band structures, we found that Ni0.3Mn0.5Co0.2CO3 and Ni0.3Mn0.5Co0.2O2 structures were semiconductors with a direct gap of 0.004 eV and 0.036 eV with their doped systems also indicating metallic characteristics. Moreover, the partial density of states for our materials and their doped systems were also found to be metallic as there was no energy band gap observed at the Fermi line. Furthermore, the elastic constants revealed that all our systems recorded 21 independent elastic constants which falls within the triclinic lattice systems. For a material to be considered mechanically stable within the triclinic system, there are conditions to be satisfied, hence Ni0.3Mn0.5Co0.2CO3 satisfied all the conditions suggesting mechanical stability while Ni0.3Mn0.5Co0.2O2 did not satisfy all the conditions implying mechanical instability. The phonon dispersion curves revealed that Ni0.3Mn0.5Co0.2CO3 was vibrationally stable while Ni0.3Mn0.5Co0.2O2 was vibrationally unstable due to the presence of negative vibrations along the Brillouin zone. Furthermore, the phonon dispersion curves for doped systems revealed that some are vibrationally stable while some are vibrationally unstable. Secondly, since the study focuses on manganese rich systems, cluster expansion technique was used to generate phases in the manganese rich side. From the results, various phases with varied concentrations and symmetries were produced by the ground-state phase diagram. The accuracy of new structures during cluster expansion fitting is indicated by the cross validation score (CVs) for all of the generated new structures being less than 5meV per active atom position.

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Abstract: Despite being the most abundant sustainable energy resource, solar energy still faces major challenges in efficient capture and long-term storage. Molecular Solar Thermal Energy Storage (MOST) systems address this issue by employing photoswitchable molecules that absorb sunlight and store energy through reversible isomerization, cyclization or other intramolecular rearrangements. Azobenzenes are attractive due to their well-characterized photoresponsive behavior; however, conventional systems are hindered by low energy density, limited energy storage duration, and a reliance on organic solvents. Here, we present the Micellar Solar Thermal Energy Storage system (MIST) approach based on micellar aggregates that operate effectively across aqueous dispersions and gel states. These systems exhibit progressively enhanced energy storage lifetimes with increasing degrees of self-assembly, while delivering competitive energy densities. The thermal stability arises from restricted molecular mobility within the self-assembled structures and is enhanced on gelation, extending the calculated thermal half-life of the cis isomer from 148 days in dimethyl sulfoxide (DMSO), to 233 days in water, and to 12.8 years in the gel state. Compared to previous azobenzene-based MOST systems, our MIST approach offers significantly extended energy storage durations and improved material processability, including water-compatible formulations and, macroscopic heat release in the gel state (up to 5.7 °C).