Re-deposition of manganese compounds on LiMn 2 O 4 electrode after Mn dissolution and its impact on the positive electrode performances are studied by a control experiment, in which the spinel electrode is stored in its charged state at elevated temperature (60 • C) to accelerate Mn dissolution. Upon storage with Li foil, the re-deposition of manganese species is marginal since the dissolved Mn 2+ ions move to the Li foil to be deposited. When stored without Li foil, however, under which the chance for re-deposition of Mn species on the spinel electrode is rather high, the dissolved Mn 2+ ions are deposited as oxide and fluoride. The depth-profiling X-ray photoelectron spectroscopy and transmission electron microscope studies illustrate that Mn-O species are deposited in the earlier period of storage, whereas the Mn-F compounds (MnF 2 ) in the later stage. Due to the deposition of highly resistive MnF 2 phase, the electrode stored for a longer period of time shows a severe cell polarization and capacity loss.Since the reversible lithium intercalation/de-intercalation was reported with the lithium manganese oxide (LiMn 2 O 4, LMO hereafter) in the mid-1980s, this spinel-structured material has been extensively studied as the positive electrode for lithium-ion batteries (LIBs). At present, the LIBs adopting this 4 V positive electrode are widely used as the power source for small electronic devices, and their consumer market seems to be expanded in the near future for electric vehicles (EVs) since this material satisfies the most-demanding requirements for EVs applications; cost, high power and safety characteristics. [1][2][3][4][5][6][7] The high power performance stems from its three-dimensional Li + diffusion channels, whereas the better safety characteristics from its superior thermal stability. That is, LMO is considered as a safer positive electrode as the onset temperature for oxygen release at its charged state is higher than that for the other positive electrode materials. 8 One critical shortcoming for this material is, however, the poor cycle stability that is mainly associated with Mn dissolution during extended cycling. 9 The Mn dissolution has been considered as the most crucial aging mechanism for LMO. Obviously, the Mn dissolution leads to a loss of active material itself from the electrode layer. Many complicated aging mechanisms are also induced by Mn dissolution; an increase in cell polarization, unwanted structural and phase changes, and formation of surface films on negative and positive electrodes. 10-18 Mn dissolution is known to degrade the negative electrode when the graphitic carbons are assembled with LMO positive electrode. Dissolved manganese ions move to the negative electrode to be deposited in the metallic state, which is accompanied by the self-discharge of lithiated graphite. The metallic Mn, which is incorporated into the solid electrolyte interphase (SEI) layer on the negative electrode, is known to induce additional electrolyte decomposition. [19][20][21] It is also known that ...
Mg-doped LiCoO 2 is synthesized by a solid-state reaction as a positive electrode material for lithium-ion batteries. The uniphase solid solution is confirmed by X-ray diffraction (XRD) and Rietveld refinements. The structural changes during charging are calculated theoretically by the general gradient approximation (GGA) ab initio method. A blue-pouched single half-cell was used to collect in-situ XRD patterns while the cell charged and discharged in the range of 3.0∼4.5 V. Good structural reversibility and symmetric cell parameter changes were observed during charging and discharging. The 'W' and inverse 'W' shapes of the a-and c-cell parameter changes, respectively, were also observed. The cell volume changes show an inverse 'W' shape. No large hysteresis occurs during the changes in the cell parameters during the charging-discharging process. The thermally stable Mg-doped LiCoO 2 is confirmed by differential scanning calorimetry (DSC) and evolved gas analysis-mass spectrometry (EGA-MS).
and stability, for use as cathodes in lithium batteries. Here, we report a completely new approach to enhance Li + extraction and transport in LiCoPO 4 through Fe doping. We show that preferential Fe occupation of the 4c sites suppresses 4a-4c antisite mixing of Li and Co, thereby stabilizing the olivine structure by compensating for the Co-encapsulating oxygen octahedron shrinkage due to Co 2+ oxidation during Li + extraction. The structural stabilization gives rise to $10% higher charge capacity at a two-fold lower resistance than the undoped counterparts besides accelerating the intercalation/extraction kinetics. Our findings provide key atomistic-level insights that pave the way for the rational design and realization of new types of metal-doped cathode materials for lithium batteries and related applications.
Nanostructured electrodes have recently received great attention as components in lithium rechargeable batteries, especially because of the high power produced by the fast kinetic properties of these unique structures. Here, we report the successful synthesis of various nanostructured morphologies of spinel lithium manganese oxide electrodes (nanorod, nanothorn sphere, and sphere) from a similarly shaped manganese dioxide precursor that was controlled with different aluminium contents by the hydrothermal method. Among these structures, nanothorn sphere structured LiAl 0.02 Mn 1.98 O 4 produces the highest discharge capacity of 129.8 mA h g À1 , excellent rate capability (94.6 mA h g À1 at 20 C, 72% of 0.2 C-rate discharge capacity) and stable cyclic retention for 50 cycles. The excellent kinetic properties of the nanothorn sphere structure are not only due to the nanothorn sphere electrode having high surface area but also because the critical amount of Al in the nanothorn sphere electrode was located at the Mn site (16d) instead of the Li site (8a).
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.