Effect of Chromium Substitution on the Lattice Vibration of Spinel Lithium Manganate: A New Interpretation of the Raman Spectrum of LiMn2O4

Intimately mixed copper, cobalt, and iron fluorides resulting from the insertion of fluorine into a LDH template

The advancement of lithium-ion batteries (LIBs) with high performance is crucial across various sectors, notably in space exploration. This advancement hinges on the development of innovative cathode materials. Our research is dedicated to pioneering a new category of cathodes using fluorinated multimetallic materials, with a specific focus on diverging from the traditional Ni, Co, and Mn-based NMC chemistries by substituting nickel and manganese with copper and iron which are more sustainable elements. Our goal is also to enhance the robustness of cathodes upon cycling by substituting oxygen with fluorine as the metal-ligand. To achieve this, an intimate composite blend of CuF2 and FeF3, through the multi-metallic template fluorination (MMTF) methodology using a layered double hydroxide (LDH) as a precursor has been designed. Each of these components was carefully selected for its distinct attributes, including high redox potential, elevated energy density, substantial theoretical capacity, and improved cyclability. The composition denoted as (Cu1.5Co0.5)2+(Fe0.75Al0.25)3+ has been selected for fluorination because it maximizes Fe3+ and Cu2+ amount in the screened LDHs. Subsequently, this particular LDH was fluorinated through solid-gas fluorination at different temperatures (200, 350, and 500 °C) using gaseous molecular fluorine (F2). A comprehensive characterization of these materials using various techniques, including X-ray diffraction (XRD), 57Fe Mössbauer spectrometry, scanning electron microscopy with energy dispersive X-ray analysis (SEM-EDX), and inductively coupled plasma analyses (ICP-AES) was conducted, and the evolution of LDH upon fluorination has revealed an intermediate porous texture particularly sensitive to hydration. Two original crystallographic phases are else obtained by fluorination: one formed by the hydration of the amorphous intermediate compound: Cu3Fe1.5Al0.5F12(H2O)12 an anti-perovskite structure and another stabilized through the combination of solid gas fluorination and LDH precursor yielding an original CoFeF5-type phase. Raman operando during cyclic voltammetry measurement applied on a sample fluorinated at 500 °C and used as a cathode in front of lithium metal was finally conducted to validate redox activity and mechanism.

Slow-Released Cationic Redox Activity Promoted Stable Anionic Redox and Suppressed Jahn-Teller Distortion in Layered Sodium Manganese Oxides

Manganese-based layered oxides are considered promising cathodes for sodium ion batteries due to their high capacity and low-cost manganese and sodium resources. Triggering the anionic redox reaction (ARR) can exceed the capacity limitation determined by conventional cationic redox. However, the unstable ARR charge compensation and Jahn-Teller distortion of Mn3+ ions readily result in structural degradation and rapid capacity fade. Here, we report a P2-type Na0.8Li0.2Mn0.7Cu0.1O2 cathode that shows a capacity retention of 84.5% at 200 mA/g after 200 cycles. Combining in situ X-ray diffraction and multi other ex situ characterizations, we reveal that the enhanced cycling stability is ascribed to a slow release of cationic redox activity which can well suppress the Jahn-Teller distortion and favor the ARR reversibility. Furthermore, density-functional theory calculations demonstrate that the inhibited interlayer migration and reduced band gap facilitate the stability and kinetic behavior of ARR. These findings provide a perspective for designing high-energy-density cathode materials with ARR activity.

Effect of lithium doping on the structural, conduction mechanism and dielectric property of MnNbO4

The development of multifunctional materials is an exceptional research area, which is aimed at enhancing the versatility of materials according to their wide fields of application. Special interest was devoted here to lithium (Li)-doped orthoniobate ANbO₄ (A = Mn), in particular, the new material Li_0.08Mn_0.92NbO₄. This compound was successfully synthesized by a solid-state method and characterized using various techniques, including X-ray diffraction (XRD), which confirmed the successful formation of an ABO₄ oxide with an orthorhombic structure and the Pmmm space group. The morphology and elemental composition were analyzed by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The vibrational study (Raman) at room temperature confirmed the existence of the NbO₄ functional group. The effects of frequency and temperature on the electrical and dielectric properties were studied using impedance spectroscopy. In addition, the diminishing of the radius of semicircular arcs in the Nyquist plots (-Z'' vs. Z') showed the semiconductor behavior of the material. The electrical conductivity followed Jonscher's power law and the conduction mechanisms were identified. The electrical investigations showed the dominant transport mechanisms in the different frequency and temperature ranges, proposing the correlated barrier hopping (CBH) model in the ferroelectric phase and the paraelectric phase. The temperature dependence in the dielectric study revealed the relaxor ferroelectric nature of Li_0.08Mn_0.92NbO₄, which correlated the frequency-dispersive dielectric spectra with the conduction mechanisms and their relaxation processes. The results demonstrate that Li-doped Li_0.08Mn_0.92NbO₄ could be used both in dielectric and electrical applications.

Photo-accelerated fast charging of lithium-ion batteries

Due to their exceptional high energy density, lithium-ion batteries are of central importance in many modern electrical devices. A serious limitation, however, is the slow charging rate used to obtain the full capacity. Thus far, there have been no ways to increase the charging rate without losses in energy density and electrochemical performance. Here we show that the charging rate of a cathode can be dramatically increased via interaction with white light. We find that a direct exposure of light to an operating LiMn₂O₄ cathode during charging leads to a remarkable lowering of the battery charging time by a factor of two or more. This enhancement is enabled by the induction of a microsecond long-lived charge separated state, consisting of Mn⁴⁺ (hole) plus electron. This results in more oxidized metal centers and ejected lithium ions are created under light and with voltage bias. We anticipate that this discovery could pave the way to the development of new fast recharging battery technologies.

Here the authors show that illumination of a lithium manganese oxide cathode can induce efficient charge-separation and electron transfer processes, thus giving rise to a new type of fast lithium-ion battery charging.

Tuning the Nanoarea Interfacial Properties for the Improved Performance of Li-Rich Polycrystalline Li-Mn-O Spinel

The nontoxicity and low cost make LiMn₂O₄ a competitive cathode material for lithium-ion batteries. LiMn₂O₄ has a high theoretical capacity (296 mAh g^-1) when cycled in the 3 and 4 V regions. However, it displays a low practical capacity (∼120 mAh g^-1) because of the unavailability of the 3 V region caused by severe Jahn-Teller distortion. The present work investigated the full utilization of LiMn₂O₄ in both 3 and 4 V by tuning the nanoscale interfacial properties. Li-rich structures at the surface and interface of the spinel material and nanograin strain were introduced to improve the performances and were achieved by grinding LiMn₂O₄ and Li₂O at 700 rpm for 10 h under an argon atmosphere. The product shows a high initial discharge capacity of 287.9 mAh g^-1 at 0.05 C between 1.2 and 4.6 V and retains 83.2% of the capacity after 50 cycles. The nanoscale interfacial structure was clarified by spherical aberration-corrected microscopy and XRD refinement, and complex occupancies of Li and Mn were found at the interface. A correlation between the interfacial properties and electrochemical performance was established, and the improved performance could be attributed to the polycrystalline nature of the material, the unique Li-rich interfacial structure, and the slightly elevated valence state of Mn. The present results may provide insight for further evaluating the complex mechanism of controlling the electrochemical performance of LiMn₂O₄.

Molten Salt Assisted Self-Assembly: Synthesis of Mesoporous LiCoO2 and LiMn2 O4 Thin Films and Investigation of Electrocatalytic Water Oxidation Performance of Lithium Cobaltate

Mesoporous thin films of transition metal lithiates (TML) belong to an important group of materials for the advancement of electrochemical systems. This study demonstrates a simple one pot method to synthesize the first examples of mesoporous LiCoO₂ and LiMn₂ O₄ thin films. Molten salt assisted self-assembly can be used to establish an easy route to produce mesoporous TML thin films. The salts (LiNO₃ and [Co(H₂ O)₆ ](NO₃ )₂ or [Mn(H₂ O)₄ ](NO₃ )₂ ) and two surfactants (10-lauryl ether and cethyltrimethylammonium bromide (CTAB) or cethyltrimethylammonium nitrate (CTAN)) form stable liquid crystalline mesophases. The charged surfactant is needed for the assembly of the necessary amount of salt in the hydrophilic domains of the mesophase, which produces stable metal lithiate pore-walls upon calcination. The films have a large pore size with a high surface area that can be increased up to 82 m² g^-1 . The method described can be adopted to synthesize other metal oxides and metal lithiates. The mesoporous thin films of LiCoO₂ show promising performance as water oxidation catalysts under pH 7 and 14 conditions. The electrodes, prepared using CTAN as the cosurfactant, display the lowest overpotentials in the literature among other LiCoO₂ systems, as low as 376 mV at 10 mA cm^-2 and 282 mV at 1 mA cm^-2 .