Accelerated Electrochemical Decomposition of Li₂O₂ under X-ray Illumination

Abstract

This work presents the first report detailing the effect of X-rays on the electrochemical decomposition of Li 2 O 2 , which is the main reaction during the charging process in a Li-O 2 battery. An operando synchrotron radiation powder X-ray diffraction (SR-PXD) experiment was performed. The results indicate that the electrochemical decomposition of Li 2 O 2 is dramatically accelerated under X-ray irradiation. The accelerated decomposition of Li 2 O 2 follows a zero-order reaction, and the decomposition rate constant is proportional to the intensity of X-ray used. A mechanism for the electrochemical decomposition of Li 2 O 2 under X-ray irradiation is proposed. These results give an insight into the charging process in Li-O 2 batteries. TOC GRAPHICS KEYWORDS:Li-O 2 battery, synchrotron-based X-ray diffraction, fast charging, operando measurement, photoelectric effect, photoelectrochemistry, light-assisted electrochemical etching 3 In 1839, the photoelectric effect was first discovered by Becquerel who found that current could be generated without any external potential when AgCl was placed in an acidic solution and illuminated while connected to a Pt electrode. In the 1950's, researchers at Bell Labs began to study the possible use of photo-electrochemical effects to convert solar energy into electric power. 1 In 1972, Fujishima and Honda first reported that UV light irradiation enhanced the electrochemical decomposition of water using TiO 2 as a photocatalyst. 2 Their work triggered a rapid development of the photo-electrochemical cell. Many fundamental and applied advances have to day been achieved in the fields of environment and energy. [3][4] In those photoelectrochemical systems, the photoactive material as a charge carrier plays a catalytic role in the reaction, and its composition does not change after each cycle of interactions. Equally, photo energy can directly speed up the electrochemical transformation of target materials, which means the substance can be electrochemically decomposed or generated under electromagnetic irradiation. UV or visible light has shown some applications in this field. 5 However, the use of X-rays as a special light source has not been reported in the electrochemical transformation of solid materials.The electrochemical decomposition of Li 2 O 2 is the charging reaction in a non-aqueous Li-O 2 battery, which largely influences the charging rate, overpotential and rechargeability of the system. 6 Besides several issues like instability of electrolytes, 7-9 poor performance of lithium metal anode, 10-11 etc., one challenge for the Li-O 2 battery is to increase the kinetics of the electrode reaction, especially for the charging process. 12 Another conundrum is that the decomposition mechanism of Li 2 O 2 is not yet clear. 13 X-ray diffraction (XRD) has been applied as a simple, useful and direct measurement to investigate the formation and decomposition of Li 2 O 2 for various designs of Li-O 2 battery. 14-18 However, the low scattering ability of lithium and 4 oxygen a...

Binder-free nitrogen-doped carbon paper electrodes derived from polypyrrole/cellulose composite for Li–O2 batteries

“…The batteries sustained 14 and 5 cycles with a capacity limit of 480 mAh·g -1 at constant current densities of 0.2 and 0.4 mA/cm 2 , respectively ( Figures S5b and 5c in SI). The cell overpotential on the 1 st cycle increased from 0.68 to 0.99 V, when raising the current density from 0.1 to 0.4 mA/cm 2 (Figures 4c-e). In order to know how the unique architecture of the NCPE benefits the battery performance, the cycling response of a Li-O 2 battery with a reference electrode based on chopped NCPE powder and binder was studied, as shown in Figure 4f.…”

“…The rechargeable Li-O 2 battery has recently attracted a great deal of attention because of its significantly higher theoretical energy density than traditional lithium-ion battery [1][2][3][4][5]. A Li-O 2 battery prototype is composed of a lithium metal anode, Li + -containing nonaqueous electrolyte, and a porous O 2 cathode (normally carbon-based materials with or without catalysts).…”

Pt/α-MnO 2 nanotube: A highly active electrocatalyst for Li–O 2 battery

“…studying only OER) [13,33,44]; and ii) the oxidation potential of PC solvent is higher than that of ether [5]. It becomes hence a model system for studying catalytic activity of x wt% Pt/M-NT samples.…”

“…Lanthanum hexaoride (LaB 6 , SRM-660) acted as a reference for calibrating the different parameters of powder diffraction instrument, such as sample-to-detector distance, wavelength, and detector tilt angle. In our previous work, the electrochemical decomposition of Li 2 O 2 was dramatically accelerated under the continuous X-ray irradiation [33]. Therefore, in order to avoid the negative influence of X-ray illumination, data were collected every 30 minute (an exposure time of 20 seconds was used to collect one on the area detector.…”

Hourglasslike nodal net semimetal in Ag2BiO3

“…The crystal structure of Ag 2 BiO 3 40 used to be very controversial because of the discrepancy between theoretical predicted metallic behaviors and experimental observed insulating results. Subsequently, some careful analyses both in experiment and theoretical verified that Ag 2 BiO 3 has three distinctive phases 41,42 with space groups of P nna, P nn2, and P n, respectively. The P nna phase is a metal and the P n phase is a semiconductor, both of which are metastable and can transform into P nn2 phase, which is a semiconducting ground state.…”