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- Liu, Chenjuan, 1988-
(författare)
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Exploration of Non-Aqueous Metal-O2 Batteries via In Operando X-ray Diffraction
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Non-aqueous metal-air (Li-O2 and Na-O2) batteries have been emerging as one of the most promising high-energy storage systems to meet the requirements for demanding applications due to their high theoretical specific energy. In the present thesis work, advanced characterization techniques are demonstrated for the exploration of metal-O2 batteries. Prominently, the electrochemical reactions occurring within the Li-O2 and Na-O2 batteries upon cycling are studied by in operando powder X-ray diffraction (XRD).In the first part, a new in operando cell with a combined form of coin cell and pouch cell is designed. In operando synchrotron radiation powder X-ray diffraction (SR-PXD) is applied to investigate the evolution of Li2O2 inside the Li-O2 cells with carbon and Ru-TiC cathodes. By quantitatively tracking the Li2O2 evolution, a two-step process during growth and oxidation is observed.This newly developed analysis technique is further applied to the Na-O2 battery system. The formation of NaO2 and the influence of the electrolyte salt are followed quantitatively by in operando SR-PXD. The results indicate that the discharge capacity of Na-O2 cells containing a weak solvating ether solvent depends heavily on the choice of the conducting salt anion, which also has impact on the growth of NaO2 particles.In addition, the stability of the discharge product in Na-O2 cells is studied. Using both ex situ and in operando XRD, the influence of sodium anode, solvent, salt and oxygen on the stability of NaO2 are quantitatively identified. These findings bring new insights into the understanding of conflicting observations of different discharge products in previous studies.In the last part, a binder-free graphene based cathode concept is developed for Li-O2 cells. The formation of discharge products and their decomposition upon charge, as well as different morphologies of the discharge products on the electrode, are demonstrated. Moreover, considering the instability of carbon based cathode materials, a new type of titanium carbide on carbon cloth cathode is designed and fabricated. With a surface modification by loading Ru nanoparticles, the titanium carbide shows enhanced oxygen reduction/evolution activity and stability. Compared with the carbon based cathode materials, titanium carbide demonstrated a higher discharge and charge efficiency.
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| 2. |
- Liu, Chenjuan, 1988-, et al.
(författare)
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Growth of NaO2 in Highly Efficient Na–O2 Batteries Revealed by Synchrotron In Operando X-ray Diffraction
- 2017
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Ingår i: ACS Energy Letters. - : American Chemical Society (ACS). - 2380-8195. ; 2, s. 2440-2444
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The development of Na–O2 batteries requires understanding the formation of reaction products, as different groups reported compounds such as sodium peroxide, sodium superoxide, and hydrated sodium peroxide as the main discharge products. In this study, we used in operando synchrotron radiation powder X-ray diffraction (SR-PXD) to (i) quantitatively track the formation of NaO2 in Na–O2 cells and (ii) measure how the growth of crystalline NaO2 is influenced by the choice of electrolyte salt. The results reveal that the discharge could be divided into two time regions and that the formation of NaO2 during the major part of the discharge reaction is highly efficient. The findings indicate that the cell with NaOTf salt exhibited higher capacity than the cell with NaPF6 salt, whereas the average domain size of NaO2 particles decreases during the discharge. This fundamental insight brings new information on the working mechanism of Na–O2 batteries.
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| 3. |
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| 4. |
- Liu, Chenjuan, 1988-
(författare)
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Li2O2 quantification in non-aqueous Li-O2 batteries with binder-free cathodes
- 2017
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The non-aqueous Li-air (Li-O2) battery has been emerging as one of the most promising high-energy storage systems to meet the requirements for electric vehicle applications due to its high theoretical energy density. In order to uncover the underlying electrochemistry and enable an informed battery design, it is crucial to gain a detailed understanding of the cell´s chemical components as well as its behavior during cycling. These two fundamental tasks are reflected in this thesis’ structure: First, advanced characterization techniques are demonstrated in the search for a novel cathode material for Li-O2 batteries. Second, the electrochemical reactions occurring within the battery upon cycling are studied by in operando powder X-ray diffraction. In the first part, a novel free-standing oxygen cathode was prepared by a facile and efficient solution-process followed by a low-temperature exfoliation, which displayed a 3-D structure arrangement of graphene foam (GF) derived from a graphene oxide (GO) gel on an aluminum substrate (GF@Al). The as prepared GF@Al was directly used as cathode in Li-O2 batteries without any binder and catalyst, delivering a high capacity about 9×104 mA h·g-1 (based on the weight of graphene) or about 60 mAh·g-1 (based on the weight of the whole electrode) at the first discharge with a current density of 100 mA·ggraphene-1. Furthermore, electrodes have been investigated by X-ray diffraction (XRD), Fourier-transform infrared reflection (FTIR), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and UV-Vis spectroscopy titration. The formation of a discharge product and its decomposition upon charge as well as different morphologies of discharge products on the electrode were observed by SEM and TEM. In the second part, the evolution of Li2O2 was investigated by synchrotron radiation powder X-ray diffraction (SR-PXD). By quantitatively tracking Li2O2 under the actual electrochemical conditions, a two-step process during growth and oxidation is observed for Li2O2. This is due to different evolution steps during the two stages of both oxygen reduction reactions (ORR) and oxygen evolution reactions (OER). By analyzing the anisotropic broadening of Li2O2 X-ray diffraction peaks, anisotropic disc-like Li2O2 grains were found to be formed rapidly in the first step of discharge, followed by a nucleation and growth of toroidal Li2O2 particles with a LiO2-like surface. During the charging process, Li2O2 was oxidized from the surface first, followed by an oxidation process with a higher decomposition rate for the bulk. This new analysis technique brings additional information on the evolution of Li2O2 in Li-O2 batteries.
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