Improvement of the Elevated Temperature Cycling of LiMn2O4 spinel for Li Ion Batteries

Battery Science & TechnologyLithium manganese oxide spinel materials have been extensively studied as a cathode material for lithium ion batteries because it is inexpensive, safe, and eco-friendly. One critical shortcoming for this material is, however, the poor cycle stability that is mainly associated with manganese dissolution during extended cycling, especially at elevated temperature (> 50 oC). To relieve the capacity fading of LiMn2O4/graphite cells caused by manganese dissolution, we develop the functional binder and separator having ion exchangeability between dissolved Mn ions and Na ions of functional materials. First of all, three ion-exchangeable binders including carboxymethyl cellulose sodium salt (CMC), poly(sodium 4-styrenesulfonate) (PSS), and alginic acid sodium salt (AGA) are compared with the conventional binder of polyvinylidene fluoride (PVdF). From the galvanostatic experiments of LiMn2O4/graphite full cells at high temperature (60 oC), the ion-exchangeable binders for graphite anode show a noticeable improvement in the capacity retention. This is attributed to that the dissolved Mn ions are trapped in the ion exchangeable binders due to ion exchange between manganese ions in electrolytes and sodium ions of binders. In other words, the ion-exchangeable binders prevent the reduction of dissolved Mn ions at the surface of graphite anode, resulting in the improvement of cycle performance. This is supported by the analysis using inductively coupled plasma mass spectrometry (ICP-MS) for Mn-dissolved electrolytes and X-ray diffraction (XRD) for lithiated graphite anode. Also, the effect of ion exchange is further examined using an ion exchangeable separator. The surface-modified separator shows the improved cycle retention of LiMn2O4/graphite full cell at 60 oC due to ion exchange between manganese ions in electrolytes and sodium ions of separators.ope

Responses of Agroecosystems to Climate Change: Specifics of Resilience in the Mid-Latitude Region

This study examines the productivity and resilience of agroecosystems in the Korean Peninsula. Having learned valuable lessons from a Chapman University project funded by the United States Department of Agriculture which concentrated on the semi-arid region of southwestern United States, our joint Korea—Chapman University team has applied similar methodologies to the Korean Peninsula, which is itself an interesting study case in the mid-latitude region. In particular, the Korean Peninsula has unique agricultural environments due to differences in political and socioeconomic systems between South Korea and North Korea. Specifically, North Korea has been suffering from food shortages due to natural disasters, land degradation and political failure. The neighboring developed country, South Korea, has a better agricultural system but a low food self-sufficiency rate. Therefore, assessing crop yield potential (Yp) in the two distinct regions will reveal vulnerability and risks of agroecosystems in the mid-latitude region under climate change and variability and for different conditions

Assessment of Agricultural Drought Considering the Hydrological Cycle and Crop Phenology in the Korean Peninsula

Hydrological changes attributable to global warming increase the severity and frequency of droughts, which in turn affect agriculture. Hence, we proposed the Standardized Agricultural Drought Index (SADI), which is a new drought index specialized for agriculture and crops, and evaluated current and expected droughts in the Korean Peninsula. The SADI applies crop phenology to the hydrological cycle, which is a basic element that assesses drought. The SADI of rice and maize was calculated using representative hydrological variables (precipitation, evapotranspiration, and runoff) of the crop growing season. In order to evaluate the effectiveness of SADI, the three-month Standardized Precipitation Index, which is a representative drought index, and rainfed crop yield were estimated together. The performance evaluation of SADI showed that the correlation between rainfed crop yield and SADI was very high compared with that of existing drought index. The results of the assessment of drought over the past three decades provided a good indication of a major drought period and differentiated the results for crops and regions. The results of two future scenarios showed common drought risks in the western plains of North Korea. Successfully validated SADIs could be effectively applied to agricultural drought assessments in light of future climate change, and would be a good example of the water-food nexus approach

Efficient High-dimensional Quantum Key Distribution with Hybrid Encoding

We propose a schematic setup of quantum key distribution (QKD) with an improved secret key rate based on high-dimensional quantum states. Two degrees-of-freedom of a single photon, orbital angular momentum modes, and multi-path modes, are used to encode secret key information. Its practical implementation consists of optical elements that are within the reach of current technologies such as a multiport interferometer. We show that the proposed feasible protocol has improved the secret key rate with much sophistication compared to the previous 2-dimensional protocol known as the detector-device-independent QKD.Comment: 10 pages, 6 figure

Assessment of Agricultural Drought Considering the Hydrological Cycle and Crop Phenology in the Korean Peninsula

Hydrological changes attributable to global warming increase the severity and frequency of droughts, which in turn affect agriculture. Hence, we proposed the Standardized Agricultural Drought Index (SADI), which is a new drought index specialized for agriculture and crops, and evaluated current and expected droughts in the Korean Peninsula. The SADI applies crop phenology to the hydrological cycle, which is a basic element that assesses drought. The SADI of rice and maize was calculated using representative hydrological variables (precipitation, evapotranspiration, and runoff) of the crop growing season. In order to evaluate the effectiveness of SADI, the three-month Standardized Precipitation Index, which is a representative drought index, and rainfed crop yield were estimated together. The performance evaluation of SADI showed that the correlation between rainfed crop yield and SADI was very high compared with that of existing drought index. The results of the assessment of drought over the past three decades provided a good indication of a major drought period and differentiated the results for crops and regions. The results of two future scenarios showed common drought risks in the western plains of North Korea. Successfully validated SADIs could be effectively applied to agricultural drought assessments in light of future climate change, and would be a good example of the water-food nexus approach