61 research outputs found
Bulk and Surface Stabilization Process of Metastable Li-Rich Disordered Rocksalt Oxyfluorides as Efficient Cathode Materials
Manganese based disordered rocksalt systems have attracted attention as Co-free and high capacity cathode materials for Li-ion batteries. However, for a practical application these materials are considered as metastable and exhibit too limited cyclability. In order to improve the structural stability of the disordered rocksalt LiMnTiOF (0 ā¤ x ā¤ 1) system during cycling, we have introduced a mild temperature heat treatment process under reducing atmosphere, which is intended to overcome the structural anomalies formed during the mechanochemical synthesis. The heat-treated samples presented better electrochemical properties, which are ascribed to a structural defect mitigation process both at the surface and in the bulk, resulting in improved crystal structure stability. In addition, the optimized particle size and the smaller BET surface area induced by the recrystallization contributes to the observed enhanced performance. Among the studied compositions, the heat treated LiMnTiOF sample displayed better electrochemical performance with a discharge capacity of 165 mAh g after 100 cycles at 0.1 C (ā¼80% of the initial capacity), when combined with further conditioning of the cells. The results point explicitly towards a guided stabilization approach, which could have a beneficial effect regarding the application of DRS oxyfluoride materials for sustainable LIBs
Multimodal characterization of carbon electrodes\u27 thermal activation for vanadium redox flow batteries
Thermal activation has proven to be a valuable procedure to improve the performance of carbon electrodes in vanadium redox flow batteries (VRFBs). This work investigates how different activation temperatures impact the rayon-based carbon felt\u27s structure, surface composition, wettability, and electrochemical activity. A unique combination of non-standard techniques, including atomic force microscopy (AFM), dynamic vapor sorption (DVS), and electrochemical impedance spectroscopy (EIS) combined with the distribution of relaxation times (DRT) analysis, was used for the first time in the context of VRFB electrodes. The wettability of the carbon felts improved, and the process impedances decreased with higher activation temperatures. However, severe carbon decomposition occurs at high activation temperatures. The optimum electrochemical performance of the carbon felts in the vanadium(IV)/vanadium(V) redox reaction was observed after activation at 400 Ā°C. Thus, we conclude that the optimum activation temperature for this type of carbon felt concerning the investigated properties is around 400 Ā°C. Furthermore, we want to highlight the successful approach of using AFM, DVS, and EIS combined with DRT analysis for an integral investigation of key properties such as structure, wettability, and performance of VRFB electrodes
Toward Better Stability and Reversibility of the Mn/MnDouble Redox Activity in Disordered Rocksalt Oxyfluoride Cathode Materials
Cation-disordered rocksalt (DRS) materials have shown good initial reversibility and facile Liinsertion and extraction in the structure at high rates. However, all of the Li-rich oxyfluorides introduced so far suffer from short cycle lifetimes and severe capacity fading. In the current study, we combine the strategy of using high-valent cations with partial substitution of oxygen anions by fluorine ions to achieve the optimal Mn/Mn double redox reaction in the composition system LiMnTiOF (0 ā¤ x ā¤ 2/3). While Ti-rich compositions correlate to an O-oxidation plateau and a partial MnāMn redox process at high voltages, owing to the presence of Ti3+ in the structure, a new composition LiMnTiOF with a lower amount of Ti shows better electrochemical performance with an initial high discharge capacity of 227 mAh g (1.5ā4.3 V window) and a Coulombic efficiency of 82% after 200 cycles with a capacity of 136 mAh g (>462 Wh kg). The structural characteristics, oxidation states, and charge-transfer mechanism have been examined as a function of composition and state of charge. The results indicate a double redox mechanism of Mn/Mn in agreement with MnāTi structural charge compensation. The findings point to a way for designing high-capacity DRS materials with multi-electron redox reactions
Reinforcing the Electrode/Electrolyte Interphases of Lithium Metal Batteries Employing Locally Concentrated Ionic Liquid Electrolytes
Lithium metal batteries (LMBs) with nickel-rich cathodes are promising candidates for next-generation high-energy-density batteries, but the lack of sufficiently protective electrode/electrolyte interphases (EEIs) limits their cyclability. Herein, trifluoromethoxybenzene is proposed as a cosolvent for locally concentrated ionic liquid electrolytes (LCILEs) to reinforce the EEIs. With a comparative study of a neat ionic liquid electrolyte (ILE) and three LCILEs employing fluorobenzene, trifluoromethylbenzene, or trifluoromethoxybenzene as cosolvents, it is revealed that the fluorinated groups tethered to the benzene ring of the cosolvents not only affect the electrolytes' ionic conductivity and fluidity, but also the EEIs' composition via adjusting the contribution of the 1-ethyl-3-methylimidazolium cation (Emim+) and bis(fluorosulfonyl)imide anion. Trifluoromethoxybenzene, as the optimal cosolvent, leads to a stable cycling of LMBs employing 5 mAh cm-2 lithium metal anodes (LMAs), 21 mg cm-2 LiNi0.8Co0.15Al0.05 (NCA) cathodes, and 4.2 mu L mAh-1 electrolytes for 150 cycles with a remarkable capacity retention of 71%, thanks to a solid electrolyte interphase rich in inorganic species on LMAs and, particularly, a uniform cathode/electrolyte interphase rich in Emim+-derived species on NCA cathodes. By contrast, the capacity retention under the same condition is only 16%, 46%, and 18% for the neat ILE and the LCILEs based on fluorobenzene and benzotrifluoride, respectively.A locally concentrated ionic liquid electrolyte based on trifluoromethoxybenzene cosolvent is proposed for lithium metal batteries with nickel-rich cathodes, through a comparative study of three fluorinated aromatic cosolvents. The generated solid electrolyte interphase rich in inorganic species on anodes and, particularly, a uniform cathode/electrolyte interphase rich in organic cation-derived species on cathodes enable stable cycling of Li/LiNi0.8Co0.15Al0.05O2 cells.imag
Metalāorganic framework derived Fe7S8 nanoparticles embedded in heteroatom-doped carbon with Lithium and Sodium storage capability
Iron sulfides are promising materials for lithium- and sodium-ion batteries owing to their high theoretical capacity and widespread abundance. Herein, the performance of an iron sulfide-carbon composite, synthesized from a Fe-based metalāorganic framework (Fe-MIL-88NH2) is reported. The material is composed of ultrafine Fe7S8 nanoparticles (<10 nm in diameter) embedded in a heteroatom (N, S, and O)-doped carbonaceous framework (Fe7S8@HD-C), and is obtained via a simple and efficient one-step sulfidation process. The Fe7S8@HD-C composite, investigated in diethylene glycol dimethyl ether-based electrolytes as anode material for lithium and sodium batteries, shows high reversible capacities (930 mAh gā1 for lithium and 675 mAh gā1 for sodium at 0.1 A gā1). In situ X-ray diffraction reveals an insertion reaction to occur in the first lithiation and sodiation steps, followed by conversion reactions. The composite electrodes show rather promising long-term cycling stability and rate capability for sodium storage in glyme electrolyte, while an improved rate capacity and long-term cycling stability (800 mAh gā1 after 300 cycles at 1 A gā1) for lithium can be achieved using conventional carbonates
Rechargeable CalciumāSulfur Batteries Enabled by an Efficient Borate-Based Electrolyte
Rechargeable metalāsulfur batteries show great promise for energy storage applications because of their potentially high energy and low cost. The multivalentāmetal based electrochemical system exhibits the particular advantage of the feasibility of dendriteāfree metal anode. Calcium (Ca) represents a promising anode material owing to the low reductive potential, high capacity, and abundant natural resources. However, calciumāsulfur (CaāS) battery technology is in an early R&D stage, facing the fundamental challenge to develop a suitable electrolyte enabling reversible electrochemical Ca deposition, and at the same time, sulfur redox reactions in the system. Herein, a study of a roomātemperature CaāS battery by employing a stable and efficient calcium tetrakis(hexafluoroisopropyloxy) borate Ca[B(hfip)] electrolyte is presented. The CaāS batteries exhibit a cell voltage of ā2.1 V (close to its thermodynamic value) and good reversibility. The mechanistic studies hint at a redox chemistry of sulfur with polysulfide/sulfide species involved in the Caābased system
Performance study of magnesium-sulfur battery using a graphene based sulfur composite cathode electrode and a non-nucleophilic Mg electrolyte
Here we report for the first time the development of a Mg rechargeable battery using a grapheneāsulfur nanocomposite as the cathode, a Mgācarbon composite as the anode and a non-nucleophilic Mg based complex in tetraglyme solvent as the electrolyte. The grapheneāsulfur nanocomposites are prepared through a new pathway by the combination of thermal and chemical precipitation methods. The Mg/S cell delivers a higher reversible capacity (448 mA h gā1), a longer cyclability (236 mA h gā1 at the end of the 50th cycle) and a better rate capability than previously described cells. The dissolution of Mg polysulfides to the anode side was studied by X-ray photoelectron spectroscopy. The use of a grapheneāsulfur composite cathode electrode, with the properties of a high surface area, a porous morphology, a very good electronic conductivity and the presence of oxygen functional groups, along with a non-nucleophilic Mg electrolyte gives an improved battery performance
VOCl as a Cathode for Rechargeable Chloride Ion Batteries
A novel room temperature rechargeable battery with VOCl cathode, lithium anode, and chloride ion transporting liquid electrolyte is described. The cell is based on the reversible transfer of chloride ions between the two electrodes. The VOCl cathode delivered an initial discharge capacity of 189ā
mAhāgā1. A reversible capacity of 113ā
mAhāgā1 was retained even after 100 cycles when cycled at a high current density of 522ā
mAāgā1. Such high cycling stability was achieved in chloride ion batteries for the first time, demonstrating the practicality of the system beyond a proof of concept model. The electrochemical reaction mechanism of the VOCl electrode in the chloride ion cell was investigated in detail by exā
situ X-ray diffraction (XRD), infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The results confirm reversible deintercalationāintercalation of chloride ions in the VOCl electrode
Synergistic Effect of Co and Mn Co-Doping on SnO2 Lithium-Ion Anodes
The incorporation of transition metals (TMs) such as Co, Fe, and Mn into SnO2 substantially improves the reversibility of the conversion and the alloying reaction when used as a negative electrode active material in lithium-ion batteries. Moreover, it was shown that the specific benefits of different TM dopants can be combined when introducing more than one dopant into the SnO2 lattice. Herein, a careful characterization of Co and Mn co-doped SnO2 via transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy and X-ray diffraction including Rietveld refinement is reported. Based on this in-depth investigation of the crystal structure and the distribution of the two TM dopants within the lattice, an ex situ X-ray photoelectron spectroscopy and ex situ X-ray absorption spectroscopy were performed to better understand the de-/lithiation mechanism and the synergistic impact of the Co and Mn co-doping. The results specifically suggest that the antithetical redox behaviour of the two dopants might play a decisive role for the enhanced reversibility of the de-/lithiation reaction
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