Synthesizing High‐Capacity Oxyfluoride Conversion Anodes by Direct Fluorination of Molybdenum Dioxide (MoO₂)

Abstract

High‐capacity metal oxide conversion anodes for lithium‐ion batteries (LIBs) are primarily limited by their poor reversibility and cycling stability. In this study, a promising approach has been developed to improve the electrochemical performance of a MoO2 anode by direct fluorination of the prelithiated MoO2. The fluorinated anode contains a mixture of crystalline MoO2 and amorphous molybdenum oxyfluoride phases, as determined from a suite of characterization methods including X‐ray diffraction, Raman spectroscopy, and X‐ray photoelectron spectroscopy, and scanning transmission electron microscopy. Electrochemical measurements indicate that fluorination facilitates the conversion reaction kinetics, which leads to increased capacity, higher coulombic efficiency, and better cycling stability as compared to the nonfluorinated samples. These results suggest that fluorination after prelithiation not only favors formation of the oxyfluoride phase but also improves the lithium‐ion diffusivity and reversibility of the conversion reaction, making it an attractive approach to address the problems of conversion electrodes. These findings provide a new route to design high‐capacity negative electrodes for LIBs.

Enhanced Oxygen Evolution Catalytic Activity of Ni3Mo3N-MoO2-NiO Nanoparticles via Synergistic Effect

“…The results illustrate that the Mo–N bond breaks, the Mo atoms are oxidized to Mo 6+ , and part of Mo 6+ ions are reduced to Mo 5+ . Because Mo 6+ has a higher electronegativity and more outermost vacant orbitals, it can accept the electron from Ni 2+ to generate Mo 5+ and Ni 3+ , thus leading to an increase in catalytic activity. , As displayed in Figure c, the M–N bonds were completely destroyed and generated the N–O bonds during the OER test. , In the O 1s spectra (Figure d), the peaks at 530.6, 531.5, 532.7, and 535.6 eV are attributed to Mo–O of MoO 3 , Ni–O, O–H, and the shoulder peak, respectively. , The above results illustrate that the Ni and Mo atoms on the surface have been oxidized to constitute the oxide layer, which improve the stability. Besides, Mo 6+ accepts the electron from Ni 2+ to convert to Mo 5+ accompanied by Ni 3+ generated during the reaction, and Ni 3+ serves as the active site to facilitate the catalytic activity.…”

“…The peaks of Ni + and Mo + bond shift to higher binding energies, suggesting the electronic structure of Ni and Mo atoms has been influenced, so the Ni + and Mo + atoms are easily oxidized to a high valence state. For the N 1s XPS spectrum (Figure d), the peak at 398.7 eV is the diffraction peak of NH and the peaks at 397.3 and 394.8 eV are derived from MN bond and Mo 3p 3/2 , respectively. , As for the O 1s spectrum (Figure e), the O 1s peaks can be broken down into three components centered at 529.6, 530.4, and 532.0 eV, which are ascertained as the NiO, MoO, and OH bonds, respectively. − Additionally, the C 1s XPS spectra are shown in Figure f. The diffraction peak at 284.8 eV corresponds to CC, the peak at 286.2 eV is CN, which proves the existence of nitrogen-doped carbon, and the peak at 287.5 eV belongs to CO. , …”

Enhancing Cycling Stability and Capacity Retention of NMC811 Cathodes by Reengineering Interfaces via Electrochemical Fluorination

“…Typically there are two main avenues for doping fluorine on the cathode surface, which are through i) high temperature fluorination-a solid-state synthesis route [26,27] or direct fluorination route by using F 2 gas as used by Dai et al for transition metal oxides, [28][29][30][31][32][33][34][35] or ii) solution mediated fluorination-the use of fluorinated solvents or additives. Due to the advantages of fluorine chemistry at the interfaces during battery operation (i.e., forming a robust SEI, [6] assisting in the retention of oxygen in the crystal lattice, [36] enhancement of capacity, and cycling stability [15,36,37] ), fluorination of cathodes have drawn significant interest as a unique technique for material functionalization.…”

Conformal LiF Stabilized Interfaces via Electrochemical Fluorination on High Voltage Spinel Cathodes (≈4.9 V) for Lithium‐Ion Batteries

“…[28][29][30][31] In order to achieve a thin surface passivating LiF layer on the cathode surface, different fluorination strategy have been studied. [32][33][34][35][36] However, forming thin LiF surface layer without changing bulk structure and morphology is challenging and so far reported techniques resulted in uncontrolled fluorination, which is deleterious to the stability of the cathodes. Therefore, a carefully reengineered cathode surface with an optimized LiF layer that permits lithium-ion conduction would be the best CEI for the stabilization of the interfaces of a high voltage cathode.…”