Seongsu Lee

New iron-based mixed-polyanion cathodes for lithium and sodium rechargeable batteries: combined first principles calculations and experimental study.

New iron-based mixed-polyanion compounds Li(x)Na(4-x)Fe(3)(PO(4))(2)(P(2)O(7)) (x = 0-3) were synthesized, and their crystal structures were determined. The new compounds contained three-dimensional (3D)sodium/lithium paths supported by P(2)O(7) pillars in the crystal. First principles calculations identified the complex 3D paths with their activation barriers and revealed them as fast ionic conductors. The reversible electrode operation was found in both Li and Na cells with capacities of one-electron reaction per Fe atom, 140 and 129 mAh g(-1), respectively. The redox potential of each phase was ∼3.4 V (vs Li) for the Li-ion cell and ∼3.2 V (vs Na) for the Na-ion cell. The properties of high power, small volume change, and high thermal stability were also recognized, presenting this new compound as a potential competitor to other iron-based electrodes such as Li(2)FeP(2)O(7), Li(2)FePO(4)F, and LiFePO(4).

Burden of osteoporosis in adults in Korea: a national health insurance database study

We evaluated the number of osteoporosis patients under treatment and secular trends in 2005–2008 in South Korea. We investigated nationwide data regarding the number of osteoporosis patients under treatment in South Korea using data from the Health Insurance Review Agency (HIRA), which includes nationwide information. Reimbursement records from the HIRA database between 1 January 2004 and 31 December 2008 were investigated. Patients aged ≥30 years old with osteoporosis were identified based on a study-defined algorithm using prescription data and diagnostic codes. During the study periods, the number of patients receiving medical treatment related to osteoporosis increased from 1,034,399 to 1,392,189 for women and from 120,496 to 171,902 for men. The calculated proportion of osteoporosis patients under treatment in the general population over 50xa0years of age was 6.1% for men and 33.3% for women, and in the general population over 30xa0years of age was 2.7% for men and 16.6% for woman. More than 40% of patients (59.1% for women; 41.2% for men) were treated with medication indicated only for osteoporosis. About 4–7% of osteoporosis patients had a past medical history suggesting a secondary cause of osteoporosis. More than 80% of all osteoporosis patients were women older than 50xa0years, reflecting the pronounced burden of osteoporosis among postmenopausal women. This study demonstrated a substantial increasing trend in medical claims related to osteoporosis in 2005–2008 among adults in Korea and a pronounced burden of osteoporosis among postmenopausal women.

Anomalous Jahn–Teller behavior in a manganese-based mixed-phosphate cathode for sodium ion batteries

We report a 3.8 V manganese-based mixed-phosphate cathode material for applications in sodium rechargeable batteries; i.e., Na4Mn3(PO4)2(P2O7). This material exhibits a largest Mn2+/Mn3+ redox potential of 3.84 V vs. Na+/Na yet reported for a manganese-based cathode, together with the largest energy density of 416 W h kg−1. We describe first-principles calculations and experimental results which show that three-dimensional Na diffusion pathways with low-activation-energy barriers enable the rapid sodium insertion and extraction at various states of charge of the Na4−xMn3(PO4)2(P2O7) electrode (where x = 0, 1, 3). Furthermore, we show that the sodium ion mobility in this crystal structure is not decreased by the structural changes induced by Jahn–Teller distortion (Mn3+), in contrast to most manganese-based electrodes, rather it is increased due to distortion, which opens up sodium diffusion channels. This feature stabilizes the material, providing high cycle stability and high power performance for sodium rechargeable batteries. The high voltage, large energy density, cycle stability and the use of low-cost Mn give Na4Mn3(PO4)2(P2O7) significant potential for applications as a cathode material for large-scale Na-ion batteries.

Tailoring a fluorophosphate as a novel 4 V cathode for lithium-ion batteries

Lithium-ion batteries, which have been widely used to power portable electronic devices, are on the verge of being applied to new automobile applications. To expand this emerging market, however, an electrode that combines fast charging capability, long-term cycle stability, and high energy density is needed. Herein, we report a novel layered lithium vanadium fluorophosphate, Li1.1Na0.4VPO4.8F0.7, as a promising positive electrode contender. This new material has two-dimensional lithium pathways and is capable of reversibly releasing and reinserting ~1.1 Li+ ions at an ideal 4 V (versus Li+/Li) to give a capacity of ~156 mAh g−1 (energy density of 624u2005Wh kg−1). Moreover, outstanding capacity retentions of 98% and 96% after 100 cycles were achieved at 60°C and room temperature, respectively. Unexpectedly high rate capability was delivered for both charge and discharge despite the large particle size (a few microns), which promises further enhancement of power density with proper nano-engineering.

Alluaudite LiMnPO4: a new Mn-based positive electrode for Li rechargeable batteries

A novel, Na-pillared LiMnPO4 (Li0.78Na0.22MnPO4) with an alluaudite structure is successfully prepared for the first time and proposed as a new positive electrode for Li rechargeable batteries. Approximately 0.8 Li+ ions are reversibly extracted from and reinserted into LiMnPO4via Mn2+/Mn3+ redox reactions. The alluaudite LiMnPO4 (a-LiMnPO4) structure is sufficiently robust during repeated Li extraction/insertion such that ∼92% of the initial capacity is retained after 50 charge/discharge cycles. An ex situ XRD study of the electrochemical cell during cycling indicates that Li de/intercalation in alluaudite LiMnPO4 occurs via the one-phase (solid–solution) reaction instead of the two-phase reaction observed in olivine LiMnPO4.

Chronic ethanol ingestion, type 2 diabetes mellitus, and brain-derived neurotrophic factor (BDNF) in rats.

Chronic alcohol consumption contributes to the development of type 2 diabetes mellitus (T2DM) while decreasing the level of brain-derived neurotrophic factor (BDNF). BDNF may be an important regulator of glucose metabolism, so it may be associated with an increased risk for T2DM in alcoholism. We evaluated the association of chronic heavy alcohol exposure, T2DM and BDNF level. Ten week-old type 2 diabetic OLETF rats and non-diabetic LETO rats of similar weight were used. The rats were randomized by weight into four treatment groups: (1) OLETF-Ethanol (O-E, n=13), (2) OLETF-Control (O-C, n=15), (3) LETO-Ethanol (L-E, n=11), and (4) LETO-Control (L-C, n=14). The ethanol groups were fed an isocaloric liquid diet containing ethanol while the control groups were fed with the same diet containing maltose-dextran over a 6-week period using a pair-feeding control model in order to regulate different caloric ingestion. After 6 weeks of feeding, an Intraperitoneal Glucose Tolerance Test (IP-GTT) was performed and BDNF levels were analyzed. Prior to IP-GTT, the mean glucose levels in the O-E, O-C, L-E, and L-C groups were 90.38±12.84, 102.13±5.04, 95.18±6.43, and 102.36±4.43mg/dL, respectively. Thirty minutes after intraperitoneal injection, the mean glucose levels were 262.62±63.77, 229.07±51.30, 163.45±26.63, and 156.64±34.42mg/dL, respectively; the increased amount of the mean glucose level in the O-E group was significantly higher than that in the O-C group (p<0.05). One hundred twenty minutes after intraperitoneal injection, the mean glucose levels were 167.38±45.37, 121.20±18.54, 106.73±6.94, and 104.57±9.49mg/dL, respectively; the increased amount of the mean glucose level in the O-E group was significantly higher than that in the O-C group (p<0.01). The difference in mean glucose levels between the O-E group and O-C group was still significant even after adjusting for time (p<0.05). Mean BDNF levels were 405.95±326.16, 618.23±462.15, 749.18±599.93, and 1172.00±839.17pg/mL, respectively; mean BDNF level in the O-E group was significantly lower than the L-C group (p<0.05). In conclusion, the results of the present study suggest that chronic heavy alcohol ingestion may aggravate T2DM and may possibly lower BDNF level.

Improved oxide-ion conductivity of NdBaInO4 by Sr doping

The oxide-ion conductivity of NdBaInO4 has been increased by Sr doping. Nd0.9Sr0.1BaInO3.95 showed the highest electrical conductivity among Nd1−xSrxBaInO4−x/2 (x = 0.0, 0.1, 0.2, and 0.3). The oxide-ion conductivity σion of Nd0.9Sr0.1BaInO3.95 (σion = 7.7 × 10−4 S cm−1) is about 20 times higher than that of NdBaInO4 (σion = 3.6 × 10−5 S cm−1) at 858 °C, and the activation energy of oxide-ion conduction is a little lower for Nd0.9Sr0.1BaInO3.95 (0.795(10) eV) than that for NdBaInO4 (0.91(4) eV). The structure analysis based on neutron powder diffraction data revealed that the Sr exists at the Nd site and oxygen vacancies are observed in Nd0.9Sr0.1BaInO3.95. This result indicates that the increase of the oxide-ion conductivity is mainly due to the increase of the carrier concentration. The bond valence-based energy landscape indicated two-dimensional oxide-ion diffusion in the (Nd,Sr)2O3 unit on the bc-plane and a decrease of the energy barrier by the substitution of Nd with Sr cations.

Direct Observation of Localized Spin Antiferromagnetic Transition in PdCrO2 by Angle-Resolved Photoemission Spectroscopy

We report the first case of the successful measurements of a localized spin antiferromagnetic transition in delafossite-type PdCrO2 by angle-resolved photoemission spectroscopy (ARPES). This demonstrates how to circumvent the shortcomings of ARPES for investigation of magnetism involved with localized spins in limited size of two-dimensional crystals or multi-layer thin films that neutron scattering can hardly study due to lack of bulk compared to surface. Also, our observations give direct evidence for the spin ordering pattern of Cr3+ ions in PdCrO2 suggested by neutron diffraction and quantum oscillation measurements, and provide a strong constraint that has to be satisfied by a microscopic mechanism for the unconventional anomalous Hall effect recently reported in this system.

Thermal expansivity of ionic clathrate hydrates including gaseous guest molecules.

Although thermal expansion is a key factor in relation to the host-guest interaction of clathrate hydrates, few studies have investigated the thermal behavior of ionic clathrate hydrates. The existence of ionic species in these hydrates creates a unique host-guest interaction compared to that of nonionic clathrate hydrates. It was revealed that X-ray diffraction cannot be used for research of tetramethylammonium hydroxide clathrate hydrates due to damage of the cations by the X-ray, which results in abnormal thermal expansion of the ionic clathrate hydrates. Hence, in the present work, the thermal expansivities of binary sII Me(4)NOD·16D(2)O and sI DClO(4)·5.5D(2)O were measured by neutron powder diffraction (NPD) in order to shed light on their thermal behavior. General correlations for the thermal behaviors of given structures were established and lattice expansions depending on the guests were compared between ionic and nonionic clathrate hydrates. The peculiar change in the thermal expansivity of binary DClO(4)·5.5D(2)O was also considered in relation to the host-guest configuration.

Lithium-excess olivine electrode for lithium rechargeable batteries

Lithium iron phosphate (LFP) has attracted tremendous attention as an electrode material for next-generation lithium-rechargeable battery systems due to the use of low-cost iron and its electrochemical stability. While the lithium diffusion in LFP, the essential property in battery operation, is relatively fast due to the one-dimensional tunnel present in the olivine crystal, the tunnel is inherently vulnerable to the presence of FeLi anti-site defects (Fe ions in Li ion sites), if any, that block the lithium diffusion and lead to inferior performance. Herein, we demonstrate that the kinetic issue arising from the FeLi defects in LFP can be completely eliminated in lithium-excess olivine LFP. The presence of an excess amount of lithium in the Fe ion sites (LiFe) energetically destabilizes the FeLi-related defects, resulting in reducing the amount of Fe defects in the tunnel. Moreover, we observe that the spinodal decomposition barrier is notably reduced in lithium-excess olivine LFP. The presence of LiFe and the absence of FeLi in lithium-excess olivine LFP additionally induce faster kinetics, resulting in an enhanced rate capability and a significantly reduced memory effect. The lithium-excess concept in the electrode crystal brings up unexpected properties for the pristine crystal and offers a novel and interesting approach to enhance the diffusivity and open up additional diffusion paths in solid-state ionic conductors.