Degradation Mechanisms of a Li-S Cell using Commercial Activated Carbon

Norihiro Togasaki,Aiko Nakao,Akari Nakai,Fujio Maeda,Seiichi Kobayashi,Tetsuya Osaka The Korean Electrochemical Society 2023 Journal of electrochemical science and technology Vol.14 No.4

In lithium-sulfur (Li-S) batteries, encapsulation of sulfur in activated carbon (AC) materials is a promising strategy for preventing the dissolution of lithium polysulfide into electrolytes and enhancing cycle life, because instead of solid-liquid-solid reactions, quasi-solid-state (QSS) reactions occur in the AC micropores. While a high weight fraction of sulfur in S/AC composites is essential for achieving a high energy density of Li-S cells, the deterioration mechanisms under such conditions are still unclear. In this study, we report the deterioration mechanisms during charge-discharge cycling when the discharge products overflow from the AC. Analysis using scanning electron microscopy and energy-dispersive X-ray spectrometry confirms that the sulfur in the S/AC composites migrates outside the AC as cycling progresses, and it is barely present in the AC after 20 cycles, which corresponds to the capacity decay of the cell. Impedance analysis clearly shows that the electrical resistance of the S/AC composite and the charge-transfer resistance of QSS reactions significantly increase as a result of sulfur migration. On the other hand, the charge-discharge cycling performance under limited-capacity conditions, where the discharge products are encapsulated inside the AC, is extremely stable. These results reveal the degradation mechanism of a Li-S cell with micro-porous carbon and provide crucial insights into the design of a S/AC composite cathode and its operating conditions needed to achieve stable cycling performance.

Determining the Facile Routes for Oxygen Evolution Reaction by <i>In Situ</i> Probing of Li-O₂ Cells with Conformal Li₂O₂ Films

Hong, Misun,Yang, Chunzhen,Wong, Raymond A.,Nakao, Aiko,Choi, Hee Cheul,Byon, Hye Ryung American Chemical Society 2018 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.140 No.20

<P>An ongoing challenge with lithium-oxygen (Li-O<SUB>2</SUB>) batteries is in deciphering the oxygen evolution reaction (OER) process related to the slow decomposition of the insulating lithium peroxide (Li<SUB>2</SUB>O<SUB>2</SUB>). Herein, we shed light on the behavior of Li<SUB>2</SUB>O<SUB>2</SUB> oxidation by exploiting various <I>in situ</I> imaging, gas analysis, and electrochemical methods. At the low potentials 3.2-3.7 V (vs Li/Li<SUP>+</SUP>), OER is exclusive to the thinner parts of the Li<SUB>2</SUB>O<SUB>2</SUB> deposits, which leads to O<SUB>2</SUB> gas evolution, followed by the concomitant release of superoxide species. At higher potentials, OER initiates at the sidewalls of the thicker Li<SUB>2</SUB>O<SUB>2</SUB>. The succeeding lateral decomposition of Li<SUB>2</SUB>O<SUB>2</SUB> indicates the preferential Li<SUP>+</SUP> and charge transport occurring at the sidewalls of Li<SUB>2</SUB>O<SUB>2</SUB>. To ameliorate the OER rate, we also investigate an alternative approach of rerouting charge carriers by using soluble redox mediators. Our <I>in situ</I> probes provide insights into the favorable charge-transport routes that can aid in promoting Li<SUB>2</SUB>O<SUB>2</SUB> decomposition.</P> [FIG OMISSION]</BR>

Structurally Tuning Li₂O₂ by Controlling the Surface Properties of Carbon Electrodes: Implications for Li–O₂ Batteries

Wong, Raymond A.,Dutta, Arghya,Yang, Chunzhen,Yamanaka, Keisuke,Ohta, Toshiaki,Nakao, Aiko,Waki, Keiko,Byon, Hye Ryung American Chemical Society 2016 Chemistry of materials Vol.28 No.21

<P>In lithium oxygen (Li-O-2) batteries, controlling the structure of lithium peroxide (Li2O2) can reduce the large overpotential of the charge process as this affects the ionic and electronic conductivities of Li2O2. We demonstrate, for the first time, the in situ structural tuning of Li2O2 during the discharge process by virtue of the surface properties of carbon nanotube electrodes. We tailored carbon nanotube surfaces to decouple oxygen functional groups, defective edges, and graphitization, which directly influence the surface-binding affinity of O-2 and LiO2. Consequently, conformal and completely amorphous Li2O2 films form in the presence of oxygen functional groups, which can facilely decompose in the subsequent charge. In contrast, crystalline Li2O2 particles grow in more ordered carbon electrodes and consequently require higher overpotential for decomposition. Our comprehensive study reveals the possibility of facile decomposition of Li2O2 by the surface engineering of carbon electrode and gives insights into the parameters to improve Li-O-2 cell performance without any additional promoters such as nanoparticles or soluble redox mediators. In all, this work provides improved understanding of the general role of carbonaceous electrode surfaces toward the enhancement of discharge capacity, charge potential, and stability.</P>

Acceptance of the Deltoid Muscle Injection of Aripiprazole Long-acting Injectable in the Patients with Schizophrenia

Hiroyuki Kamei,Yuki Homma,Ippei Takeuchi,Genta Hajitsu,Kaori Tozawa,Masakazu Hatano,Aiko Fukui,Manako Hanya,Shigeki Yamada,Nakao Iwata 대한정신약물학회 2020 CLINICAL PSYCHOPHARMACOLOGY AND NEUROSCIENCE Vol.18 No.1

Objective: To improve poor medication adherence in schizophrenic patients, long-acting injectable (LAI) antipsychotics are used. However, it has not yet become common in Japan. Recently, aripiprazole LAI was approved for alternative injection into the deltoid muscle in addition to the gluteal muscle. The acceptance for the proposal to switch from gluteal to deltoid injections of aripiprazole LAI was investigated. Methods: The subjects were 32 outpatients with schizophrenia who had continuously received aripiprazole LAI administration into the gluteal muscle for ≥ 6 months. In the patients who had continued deltoid injection for 3 months after switching, the changes in the pain and shame in comparison with gluteal injections were evaluated. Results: Switching to the deltoid injection was chosen by 17 out of 32 patients. Three months later, 9 patients were still receiving deltoid injections with highly rated satisfaction. The main reasons for switching to deltoid injections included the pain and shame associated with gluteal injections. The main reason for returning to the gluteal injection was the pain experienced from the injection in the deltoid. Conclusion: The option to select the injected area was based on the amount of pain in the deltoid and gluteal sites, leading to the widespread use of aripiprazole LAI.

Influence of perfluorinated ionomer in PEDOT:PSS on the rectification and degradation of organic photovoltaic cells

Howells, Calvyn T.,Saylan, Sueda,Kim, Haeri,Marbou, Khalid,Aoyama, Tetsua,Nakao, Aiko,Uchiyama, Masanobu,Samuel, Ifor D. W.,Kim, Dong-Wook,Dahlem, Marcus S.,André,, Pascal The Royal Society of Chemistry 2018 Journal of Materials Chemistry A Vol.6 No.33

<P>Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is widely used to build optoelectronic devices. However, as a hygroscopic water-based acidic material, it brings major concerns for stability and degradation, resulting in an intense effort to replace it in organic photovoltaic (OPV) devices. In this work, we focus on the perfluorinated ionomer (PFI) polymeric additive to PEDOT:PSS. We demonstrate that it can reduce the relative amplitude of OPV device burn-in, and find two distinct regimes of influence. At low concentrations there is a subtle effect on wetting and work function, for instance, with a detrimental impact on the device characteristics, and above a threshold it changes the electronic and device properties. The abrupt threshold in the conducting polymer occurs for PFI concentrations greater than or equal to the PSS concentration and was revealed by monitoring variations in transmission, topography, work-function, wettability and OPV device characteristics. Below this PFI concentration threshold, the power conversion efficiency (PCE) of OPVs based on poly(3-hexylthiophene-2,5-diyl):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM) are impaired largely by low fill-factors due to poor charge extraction. Above the PFI concentration threshold, we recover the PCE before it is improved beyond the pristine PEDOT:PSS layer based OPV devices. Supplementary to the performance enhancement, PFI improves OPV device stability and lifetime. Our degradation study leads to the conclusion that PFI prevents water from diffusing to and from the hygroscopic PEDOT:PSS layer, which slows down the deterioration of the PEDOT:PSS layer and the aluminum electrode. These findings reveal mechanisms and opportunities that should be taken into consideration when developing components to inhibit OPV degradation.</P>

Enhanced organic solar cells efficiency through electronic and electro-optic effects resulting from charge transfers in polymer hole transport blends

Howells, Calvyn T.,Marbou, Khalid,Kim, Haeri,Lee, Kwang Jin,Heinrich, Benoî,t,Kim, Sang Jun,Nakao, Aiko,Aoyama, Tetsua,Furukawa, Seiichi,Kim, Ju-Hyung,Kim, Eunsun,Mathevet, Fabrice,Mery, St&eacut The Royal Society of Chemistry 2016 Journal of Materials Chemistry A Vol.4 No.11

<P>We demonstrate that blending fluorinated molecules in PEDOT:PSS hole transport layers (HTL) induces charge transfers which impact on both charge extraction and photogeneration within organic photovoltaic (OPV) devices. OPVs fabricated with modified HTL and two photoactive polymer blends led systematically to power conversion efficiencies (PCE) increases, with PTB7:PC70BM blend exhibiting PCE of ∼8.3%,<I>i.e.</I>∼15% increase compared to pristine HTL devices. A reduced device-to-device characteristics variations was also noticed when fluorinated additives were used to modify the PEDOT:PSS. Shading lights onto the effect of HTL fluorination, we show that the morphology of the polymer:PCBM blends remains surprisingly unaffected by the fluorinated HTL surface energy but that, instead, the OPVs are impacted not only by the HTL electronic properties (work function, dipole layer, open circuit voltage, charge transfer dynamic) but also by alteration of the complex refractive indices (photogeneration, short circuit current density, external quantum efficiencies, electro-optic modelling). Both mechanisms find their origin in fluorination induced charge transfers. This work points towards fluorination as a promising strategy toward combining both external quantum efficiency modulation and power conversion efficiency enhancement in OPVs. Charge transfers could also be used more broadly to tune the optical constants and electric field distribution, as well as to reduce interfacial charge recombinations within OPVs.</P>