Search

Recently, many researchers focus on Na-ion batteries as an alternative to Li-ion batteries, owing to their low cost and high natural abundance. However, they suffer from low electrochemical performance and large volume expansion, which makes difficult to industrial application. Therefore, various strategies have been proposed to address the current issues, such as particle-size control, surface-coating, and application of electrode material with various crystal structures. Herein, we briefly introduce and discuss the recent research with development trend of cathode material for Na-ion batteries.

An amorphorized Cu(PO3)2/C composite (A-CPO/C) achieves outstanding electrochemical performances compared to a low-crystalline Cu(PO3)2 (LC-CPO/C) composite.

Cellulose nanocrystals (CNCs) have emerged as a promising templating material due to unique features, such as high surface area, surface hydroxyl groups and rod-like shape, which allow for sustainable nanoscale control of advanced functional materials. Especially, such high surface functionality and specific morphology can be imparted on the resultant nanomaterials with beneficial properties during templating. Here, we present synthesis of one-dimensional (1D) nanostructured vanadium oxides (NVOs), such as VO2(B) and V2O5‧nH2O nanobelts (NBs), with single- crystalline by hydrothermal treatment using CNCs as a sacrificial template. Importantly, the single-crystal vanadium oxide nanobelts exhibits the enhanced electrochemical performance of Li ion batteries with high specific capacity (>300 mAh/g) and long lifespan (>244 mAh/g at 50 cycles) compared to the polycrystalline nanoflakes (NFs) counterpart. Furthermore, we suggest that during hydrothermal treatment the sacrificial CNCs template-derived carbon is beneficial for electron transfer in cathode materials. Thus, we demonstrate that the utilization of CNCs templating to develop novel single-crystalline oxide cathode nanomaterials can provide a fruitful pathway for extraordinary electrochemical performance of next-generation alkaline batteries.

Cylindrical-type cells have been widely adopted by major battery and electric vehicle manufacturers owing to their price competitiveness, safety, and easy expandability. However, placement of electrodes at the core of cylindrical cells is currently restricted because of high electrode curvature and the lack of specialized electrodes and electrode materials. Here, we report the realization of highly flexible high-energy-density electrodes (active material loading of >98.4%) that can be used at the cores of cylindrical cells. The improved properties result from the introduction of a multifunctional poly(melamine-co-formaldehyde) (MF copolymer) additive, which yields a relatively more fluidic and well-dispersed slurry using only 0.08 wt %. MF copolymer-mediated formation of completely wrapped CNT/PVDF networks on LiCoO2 (LCO) and accompanying contact enhancement between LCO and carbon nanotubes (CNTs) resulted in an increase of electrical and mechanical properties of the two types (composites with or without collectors) of electrodes compared with those of additive-free electrodes. Flexibility tests were carried out by rolling electrodes onto cylinder substrates (diameters of ca. 1 and 10 mm); this process resulted in relatively lower resistance changes of the MF copolymer-containing electrodes than for the reference electrodes. In addition, capacity retention after 100 cycles for cells with and without MF copolymers was approximately 10-20% better for the samples with the MF copolymer than for those without. CNT/PVDF networks with MF copolymers were proven to induce a relatively thin and stable cathode electrolyte interface layer accompanying the chemical bond formation during cycling.

Functional separators, which are chemically modified and coated with nanostructured materials, are considered an effective and economical approach to suppressing the shuttle effect of lithium polysulfide (LiPS) and promoting the conversion kinetics of sulfur cathodes. Herein, we report cobalt-aluminum-layered double hydroxide quantum dots (LDH-QDs) deposited with nitrogen-doped graphene (NG) as a bifunctional separator for lithium-sulfur batteries (LSBs). The mesoporous LDH-QDs/NG hybrids possess abundant active sites of Co2+ and hydroxide groups, which result in capturing LiPSs through strong chemical interactions and accelerating the redox kinetics of the conversion reaction, as confirmed through X-ray photoelectron spectroscopy, adsorption tests, Li2S nucleation tests, and electrokinetic analyses of the LiPS conversion. The resulting LDH-QDs/NG hybrid-coated polypropylene (LDH-QDs/NG/PP) separator, with an average thickness of ∼17 μm, has a high ionic conductivity of 2.67 mS cm-1. Consequently, the LSB cells with the LDH-QDs/NG/PP separator can deliver a high discharge capacity of 1227.48 mAh g-1 at 0.1C along with a low capacity decay rate of 0.041% per cycle over 1200 cycles at 1.0C.

High-performance cathode materials for K-ion batteries require large K+ diffusion pathways and numerous K+ sites in the stable crystal structure. Herein, we investigate K1.5VOPO4F0.5 composed of three-dimensionally interconnected [V2O10F] bi-octahedra and [PO4] tetrahedra as a promising cathode material for K-ion batteries using a combined computational and experimental approach. First-principles calculation results reveal that K+ ions can be facilely diffused along large two-dimensional pathways in the K1.5VOPO4F0.5 structure and that numerous K+ ions can be reversibly de/intercalated in the available voltage range, demonstrating the potential of K1.5VOPO4F0.5 to deliver outstanding electrochemical performance in a K-ion battery system. At a current rate of C/20 (1C = 116 mA g−1), the specific capacity of K1.5VOPO4F0.5 is retained up to ∼116 mA h g−1 with a high average operation voltage of ∼3.8 V (vs. K+/K), corresponding to reversible de/intercalation of ∼1 mol K+ in the structure. Even at 5C, K1.5VOPO4F0.5 delivers ∼79% of the capacity measured at C/20, indicating its excellent power-capability despite the large ionic size of K+. Moreover, K1.5VOPO4F0.5 delivers excellent cycle performance, with ∼86% retention of the initial capacity after 300 cycles at 1C and a high coulombic efficiency of over 99%. Combined studies using ex situ XANES analyses and first-principles calculation indicate occurrence of V4+/V5+ redox reaction of K1.5VOPO4F0.5 for its high operation voltage. We believe that our findings will provide highly useful guidance for the discovery of high-performance electrode materials for rechargeable batteries.

De/intercalation of K+ ions results in more severe structural change and volume expansion/shrinkage than that of other monovalent ions such as Li+ and Na+ because of the larger K+-ion size. Thus, it is important to develop novel cathode materials with stable three-dimensional crystal structure and large K+ diffusion pathways to prevent severe structural change during repeated K+ de/intercalation. Here, we introduce K4[Mn2Fe](PO4)2(P2O7) composed of three-dimensionally interconnected [Mn, Fe]O6 octahedra and PO4 tetrahedra as a promising cathode material for K-ion batteries. We demonstrate the outstanding electrochemical properties and reaction mechanism of K4[Mn2Fe](PO4)2(P2O7) in a K-ion battery system through combined studies using various experimental techniques and first-principles calculation. K4[Mn2Fe](PO4)2(P2O7) delivers ∼110 mA h g−1 with a high average operation voltage of 3.5 V (vs. K+/K) at C/20 (1C = 117 mA g−1). Even at 5C, its specific capacity is ∼85 mA h g−1, corresponding to ∼77% of the capacity measured at C/20. In addition, K4[Mn2Fe](PO4)2(P2O7) exhibits an outstanding capacity retention of ∼83% after 300 cycles at C/3 with a high coulombic efficiency of more than 99%. These findings confirm the importance of a stable three-dimensional crystal structure for high-performance K-ion batteries.

To improve the thermal stability and intrinsically sluggish kinetics of oxygen electrode reactions in solid oxide fuel cells (SOFCs) and reversible protonic ceramic cells (RPCCs) at intermediate temperatures, a novel layered swedenborgite structure Y0.8Er0.2BaCo3.2Ga0.8O7+δ (YEBCG) catalyst is introduced as an alternative to perovskite materials that contain cobalt. The thermal expansion coefficient of YEBCG is 8.41 × 10−6 K−1, which is relatively well matched to the state-of-the-art proton-conducting and oxygen-ion-conducting electrolytes. The chemical bulk diffusion and surface exchange coefficients of YEBCG are 7.12 × 10−4 and 8.01 × 10−3 cm2 s−1, respectively, at 650 °C, which leads to much faster action than with state-of-art perovskite structured materials at intermediate temperatures. The maximum power densities of YEBCG cells are notably high, reaching 0.77 and 0.83 W cm−2 at 650 °C in SOFC and protonic ceramic fuel cell modes, respectively. Under electrolysis, the YEBCG cells achieve outstanding current densities of −0.61 and −4.42 A cm−2 at 500 and 700 °C, respectively, under an applied voltage of 1.4 V. Furthermore, the RPCC with YEBCG present no degradation over an entire 1000 h in fuel cell and electrolysis cell modes. These results demonstrate the excellent properties, including good durability, of the YEBCG air electrode when used in high performance SOFCs and RPCCs.

Although layered-type cathode materials for lithium-ion batteries (LIBs) have received great attention due to their large gravimetric energy density, those for potassium rechargeable batteries (PRBs) just deliver small and limited energy density due to the large structural change and phase transition during de/intercalation of K+ ions with a large ionic size. Thus, a new approach is required for achieving high energy densities. A cathode material that results in ultrahigh energy density for potassium rechargeable batteries (PRBs) based on the conversion reaction of K–SO4–Cu in the system was developed. To maximize the electrochemical performance, a copper-sulfate/carbon nanocomposite (hereafter denoted as N-CSO/C) was prepared using a simple high-energy ball-milling process. At a current density of 12 mA g−1, the conversion reaction of K–SO4–Cu in the PRB system resulted in a specific capacity of ∼240 mA h g−1 with an average operating voltage of ∼2.8 V (vs. K+/K). This capacity and the resulting energy density are larger than those of other cathode materials for PRBs reported to date. After 200 cycles at 360 mA g−1, N-CSO/C retained ∼70% of the initial capacity. The overall reversible reaction mechanism of K–SO4–Cu in N-CSO/C in the PRB system was investigated through combined studies using first-principles calculation and various experimental techniques.

Despite the high energy density of layered-type cathode materials for Na-ion batteries, their two-dimensional crystal structure suffers a large volume change and phase transition during Na+ de/intercalation, which often results in their poor cycling performances. Thus, a robust three-dimensional framework with minimal structural change is required for stable electrochemical sodium storage. Here, we introduce an earth-abundant element-based trigonal-type Na–Fe–F compound (Na2Fe2F7) with three-dimensionally interconnected FeF6 octahedra and three-dimensional Na+ diffusion pathways. Through combined studies using first-principles calculations and experiments, we confirm that Na2Fe2F7 delivers excellent power-capability due to large three-dimensional Na+ diffusion pathways as well as ultra-long cycling performance due to negligible structural change during Na+ de/intercalation. These results will guide new insights for material discovery for high performance rechargeable batteries.

We report rhombohedral-Fe2(SO4)3 as a promising cathode material for potassium-ion batteries. Detailed structure information for rhombohedral-Fe2(SO4)3 was obtained using X-ray diffraction with Rietveld refinement. Based on the structural information, possible atomic sites for K ions and ion diffusion pathway in the structure were determined using bond-valence energy landscape analyses. At C/20 (1C = 112 mA g−1), rhombohedral-KxFe2(SO4)3 delivered a specific capacity of ~100 mAh g−1 an average operation voltage of ~3.3 V (vs. K+/K), corresponding to reversible de/intercalation of ~1.78 mol K+ ions. Moreover, even at 5C, rhombohedral-KxFe2(SO4)3 exhibited capacity retention of ~80% of the capacity measured at C/20, indicating the outstanding power-capability. After 300 cycles at 2C, rhombohedral-KxFe2(SO4)3 maintained ~83% of its initial specific capacity with high Coulombic efficiency of more than 99%. Operando XRD analyses revealed that the XRD peaks of rhombohedral KxFe2(SO4)3 monotonously shifted during K+ de/intercalation, indicating a single phase reaction. First-principles calculation confirmed the good agreement between the theoretical properties of rhombohedral-KxFe2(SO4)3 and the experimental results, including the average operation voltage, power-capability, and phase reaction.

As post-harvest processes of onions are carried by a 20 kg-net package which results in high-cost and lowefficiency, especially, the insufficient drying and physical damage of onions after harvesting leads to a huge second loss in storage, we had developed a low-cost, high-efficiency post-harvest bulk handling machinery system by collecting onions on a farm using ton-bags, drying with forced air circulation, and sorting/packaging. The post-harvest bulk handling machinery system consisted of 6 devices, and this study designed an automatic feed hopper with a feeding rate control device, an inclined belt conveyor with a two-step chute, and an automatic pallet unloading device for feeding onions into the sorting/packing line. This study also analyzed the performance and control of the total system. The device had 1-ton handling capacity, but the operational condition was set to increase the capacity. The three-step filling method of pallet by the velocity control of the inclined belt conveyor was applied in the post-harvest bulk handling machinery system for the prevention of physical damage. If one worker was set to operate the total system, the time required to complete one palletized load was approximately 5 minutes and 5 seconds. The calculated daily handling capacity was approximately 94 tons, when the daily actual working time was 8 hours. When the developed system was applied to the managerial size of 2,000 ton, the processing cost per ton of the system was decreased by 19.5%, compared with the existing 20 kg-net package-based handling. The developed post-harvest bulk handling machinery system would be a good substitute for the rapid decline and aging of rural labor.

Morphology control of a graphene nanosheet (GNS) is important for graphene-based battery electrodes to exhibit the increased practical surface area and the enhanced ion diffusion into the nanosheets. Nevertheless, it is very difficult to minutely control the shape of graphene nanosheets based on the conventional GNS suspension methods. In this work, we fabricated wrinkle textures of free-standing GNS for large area using Langmuir–Schaefer technique. The wrinkles are oriented vertically to the direction of the monolayer compression. The textured structure of GNS was obtained by cross-deposition of each layer with controlling the orientation of the wrinkle direction. These wrinkles can cause Li-ion to diffuse into the voids created by them and raise the specific surface area between the GNSs. Consequently, as a prospective anode for Li-ion battery, the wrinkled GNS multilayer, exhibits the high specific capacity of ~ 740 mAh g−1 at 100 mA g−1 and the great power capability with ~ 404 mAh g−1 being delivered even at 2 A g−1. Furthermore, outstanding cycle performance of the wrinkled GNS multilayer is achieved over 200 cycles at 300 mA g−1 with high Coulombic efficiency of ~ 96%.

We introduce K4Fe3(PO4)2(P2O7) as a novel cathode material with superior electrochemical performance for K-ion batteries. First-principles calculation is used to predict the theoretical properties and detailed K+ storage mechanism of K4Fe3(PO4)2(P2O7), which are consistent with experimental results. K4Fe3(PO4)2(P2O7) exhibits a large specific discharge capacity of ~118 mAh g−1, approaching the theoretical capacity, at C/20 (1C ​= ​120 ​mA ​g−1) in the voltage range of 2.1–4.1V (vs. K+/K), allowing ~3 ​mol of K+ de/intercalation per formula unit with a small volume change of ~4% during charge/discharge. Even at 5C, up to ~70% of its theoretical specific capacity is retained, and this outstanding power-capability is related to the low activation barrier energy for K+ diffusion, as verified through first-principles calculations. Furthermore, K4Fe3(PO4)2(P2O7) exhibits excellent cyclability with retention of ~82% of the initial capacity after 500 cycles at 5C. The above theoretical and experimental results suggest the feasibility of using K4Fe3(PO4)2(P2O7) as a cathode material for rechargeable potassium batteries.

Herein, we propose P′2-Kx[Ni0.05Mn0.95]O2 as a promising cathode material for high-energy-density potassium-ion batteries (KIBs). The P′2-K0.83[Ni0.05Mn0.95]O2 delivers a high discharge capacity of 155 ​mAh g−1 (52 ​mA ​g−1) as well as a high energy density of 420 ​Wh kg−1 in the voltage range of 1.5–4.3 ​V. Surprisingly, the fast K-ion migration in the P′2-K0.83[Ni0.05Mn0.95]O2 structure with a low activation barrier energy of ~271 ​meV enables achievement of high capacity at high currents, 78 ​mAh g−1 ​at 2600 ​mA ​g−1, as well as long-term cycling stability with capacity retention of ~77% after 500 cycles at 520 ​mA ​g−1. Operando synchrotron X-ray diffraction analysis reveals that P′2-K0.83[Ni0.05Mn0.95]O2 retains the P′2-phase without P′2-OP4 phase transition during charge/discharge in the voltage range of 1.5–4.3 ​V, which is abnormal compared to the other P′2-based layered cathode materials for sodium-ion batteries, being responsible for the long-term cycle stability of P′2-K0.83[Ni0.05Mn0.95]O2. First-principles calculation results indicate that the excellent electrochemical performance results from the structural stability associated with a single -phase reaction upon K+ extraction/insertion out of/into the host structure. The remarkable potassium storage capability of P′2-K0.83[Ni0.05Mn0.95]O2 makes it a promising cathode candidate for KIBs.

We report the nano-sized CuSO4–carbon nanotube composite (nano-CuSO4/C) as a novel conversion-based cathode material for Na-ion batteries (NIBs). The nano-CuSO4/C undergoes a conversion reaction during the charge/discharge process with a high redox potential of ~2.7 V (vs. Na+/Na) and the highest reported energy density for NIB cathode materials. Nano-CuSO4/C exhibits excellent electrochemical performance, with a specific capacity of ~335 mAh g−1 at a rate of C/30 (1C = 335 mA g−1), and even at 5C, its capacity is maintained up to ~204 mAh g−1, corresponding to ~61% of the theoretical capacity. Furthermore, nano-CuSO4/C delivers outstanding capacity retention of ~72% over 300 cycles at 2C with high coulombic efficiency of more than 99%. We confirm the reversible sodium storage mechanism on nano-CuSO4/C under Na-ion battery system using various analyses, such as operando/ex situ X-ray diffraction, X-ray absorption near edge structure spectroscopy, extended X-ray absorption fine structure spectroscopy, transmission electron microscopy, and time-of-flight secondary-ion mass spectroscopy. CuSO4 is transformed into Cu0 and Na2SO4 during the discharge (reduction) process, and the original CuSO4 is recovered during the charge (oxidation) process. This fundamental understanding of CuSO4 provides insight for the use of high-capacity conversion-based cathode materials in NIBs.

To facilitate the practical realization of sodium-ion batteries, the energy density, determined by the output operating voltage and/or capacity, needs to be improved to the level of commercial Li-ion batteries. Herein, O3-type Na0.98Ca0.01[Ni0.5Mn0.5]O2 is synthesized by incorporating Ca2+ into the NaO6 octahedron of Na[Ni0.5Mn0.5]O2 and its potential use as a cathode material for high energy density SIBs is demonstrated. The ionic radius of calcium (≈1.00 A) is similar to that of sodium (≈1.02 A); hence, it is energetically favorable for calcium to occupy sites in the sodium layers. Within a wide operating voltage range of 2.0–4.3 V, O3-type Na0.98Ca0.01[Ni0.5Mn0.5]O2 exhibits a reversible O3–P3–O3 phase transition with small volume changes compared to Ca-free Na[Ni0.5Mn0.5]O2 because of the strong interaction between Ca2+ and O2− and delivers a high reversible capacity of 209 mA h g−1 at 15 mA g−1 with improved cycling stability. Moreover, Ca substitution improves the practically useful aspects such as thermal and air stability. A prototype pouch full cell with a hard carbon anode shows an excellent capacity retention of 67% over 300 cycles. Thus, this study provides an efficient and simple method to boost the performance and applicability of layered oxide cathode materials for practical applications.

Although anionic-redox-based layered oxide materials have attracted great attention as promising cathodes for Na-ion batteries because of their high practical capacities, they suffer from undesirable structural degradation, resulting in the poor electrochemical behavior. Moreover, the occurrence of stable anionic-redox reaction without the use of expensive elements such as Li, Co, and Ni is considered one of the most important issues for high-energy and low-cost Na-ion batteries. Herein, using first-principles calculation and various experimental techniques, we investigate the combination of vacancy (□) and Ti4+ cations in the transition-metal sites to enable outstanding anionic-redox-based electrochemical performance in the Na-ion battery system. The presence of vacancies in the P2-type Na0.56[Ti0.1Mn0.76□0.14]O2 structure suppresses the large structural change such as the P2–OP4 phase transition, and Ti4+ cations in the structure result in selectively oxidized oxygen ions with structural stabilization during Na+ deintercalation in the high-voltage region. The high structural stability of P2-type Na0.56[Ti0.1Mn0.76□0.14]O2 enables not only the high specific capacity of 224.92 mAh g−1 at 13 mA g−1 (1C = 264.1 mA g−1) with an average potential of ∼2.62 V (vs Na+/Na) but also excellent cycle performance with a capacity retention of ∼80.38% after 200 cycles at 52 mA g−1 with high coulombic efficiencies above 99%. Although there are some issues such as low Na contents in the as-prepared state, these findings suggest potential strategies to stabilize the anionic-redox reaction and structure in layered-oxide cathodes for high-energy and low-cost Na-ion batteries.

We report on Na4[Mn1.5Co1.5](PO4)2(P2O7) as a high-energy-density cathode material for sodium-ion batteries. Detailed structural information for Na4[Mn1.5Co1.5](PO4)2(P2O7) is obtained from Rietvel...

Na2FePO4F encircled by a nanolayer composed of a conductive polymer, poly(3,4-ethylenedioxythiophene) (PEDOT), is prepared using a simple low-temperature process, and X-ray diffraction analysis indicates that the Na2FePO4F–PEDOT composite is the pure phase without any impurities. The existence and uniform encapsulation of PEDOT on the surface of the Na2FePO4F particles are clearly confirmed through Fourier-transform infrared spectroscopy and transmission electron microscopy. The PEDOT coating results in remarkably enhanced electrochemical performance compared with that of pristine Na2FePO4F. At C/5 (1C = 124 mA g−1), the Na2FePO4F–PEDOT composite retains a specific capacity of ∼123.1 mAh g−1, which is close to its theoretical capacity. Even at 10C, the Na2FePO4F–PEDOT composite delivers a capacity of ∼76.1 mAh g−1, which is ∼10 times higher than that of pristine Na2FePO4F under the same conditions. Furthermore, the Na2FePO4F–PEDOT composite maintains ∼70% of its initial discharge capacity over 700 cycles at 1C.

We propose P3-K0.54[Co0.5Mn0.5]O2, which is rationally designed as a promising cathode material for high-performance potassium-ion batteries (KIBs). Its composition adopts the use of the valence state of Mn above 3.5 + to minimize the disruptive effect of Jahn–Teller distortion in the MnO6 octahedra during the electrochemical reaction. Unlike other types of layered materials that suffer from the sluggish diffusion of large potassium ions accompanying multi-step voltage profiles, P3-K0.54[Co0.5Mn0.5]O2 delivers a high specific discharge capacity of 120.4 mAh (g-oxide)−1 with smooth charge and discharge curves. First-principles calculations predict an activation barrier energy of ∼260 meV for a large K+ diffusion, which is comparable to those observed in conventional layered cathode materials for lithium-ion batteries. As a result, even at 500 mA g−1, P3-K0.54[Co0.5Mn0.5]O2 is able to deliver a high discharge capacity of 78 mAh g−1, which is a retention of 65% versus the capacity obtained at 20 mA g−1. Combination studies using operando X-ray diffraction, the ex-situ X-ray absorption near-edge structure, and first-principles calculations elucidate the nature of the excellent potassium storage mechanism of K0.54[Co0.5Mn0.5]O2. This work provides a new insight for the development of efficient cathode materials for KIBs.

In this study, the effect of Zn doping on the electrochemical properties of P2-Na2/3[Mn1−xZnx]O2 (x = 0.0, 0.1, 0.2, 0.3) is investigated for the first time. The P2-Na2/3[Mn0.7Zn0.3]O2 electrode deliveres a specific discharge capacity of approximately 190 mAh g−1 based on the oxygen-redox reaction (O2−/O1−), after which the Mn4+/Mn3+ redox reaction contributes to the capacity. The cycling performance of the P2-Na2/3[Mn0.7Zn0.3]O2 electrode is also greatly enhanced compared with that of the P2-Na2/3MnO2 electrode (capacity retention of 80% vs. 30% after 200 cycles). This improved cyclability is due to the suppression of cooperative Jahn–Teller distortion as well as stabilization of the structure by the electrochemically inactive Zn2+ ions. First-principle calculations and experimental analysis, including X-ray photoelectron spectroscopy and X-ray absorption near edge structure spectroscopy, clearly confirms that the Zn2+ substitution in P2-Na2/3MnO2 enables the O2−/O1− redox reaction. In addition, time-of-flight secondary ion mass spectroscopy analysis reveals that no sodium carbonates forms on the electrode surface. Our findings provide a potential new path to utilize cost-effective Mn-rich cathode materials for sodium-ion batteries via not only cationic redox but also anodic redox.

The effect of Nb5+ doping on the electrochemical and structural characteristics of NaTi2(PO4)3 was investigated. The Nb5+ substitution lowered the band gap energy from 2.8 to 1.4 eV according to density functional theory calculations. Subsequent carbonization of pitch carbon on the surface of NaNbxTi2−x(PO4)3 (x = 0.05) significantly increased the electrical conductivity, thereby improving the capacity and high-rate capability. The excellent cyclability and superior electrode performance result from facile Na+ insertion and extraction that occur via a biphasic redox mechanism, namely, the Ti4+/3+ redox couple for the cathode and a sequence of two biphasic redox reactions associated with the Ti3+/2+ redox couple for the anode, as revealed by operando X-ray diffraction and ex situ X-ray absorption spectroscopic studies. Moreover, the possibility of application of Na2.9Nb0.05Ti1.95(PO4)3 as both a cathode and anode material was demonstrated in a symmetric cell, which delivered a capacity of 105 mA h g−1 after 100 cycles at 0.2C with a capacity retention of 83%.

Although fumigation of affected trees is the common control methodof the pinewood nematode, a causal agent of pine wilt disease,the treatment causes environmental problems and is expensive.This stu...

K-ion batteries (KIB) have attracted considerable attention as a potential alternative to Li-ion batteries because of their low cost and high energy density. However, their development and durability have been severely limited by the lack of suitable cathodes with high capacity and good cycle life. Here, we prepare a low-cost Mn-based layered oxide, P2-type K0.75[Mn0.8Ni0.1Fe0.1]O2 (P2-K0.75MNFO2), via an electrochemical ion-exchange process and demonstrate its excellent K storage performance as a cathode for KIBs. During the charge–discharge process, P2-K0.75MNFO2 can release and store considerable amounts (∼0.5 mol) of K+ ions without multiple phase transitions in the voltage range of 1.5–3.9 V (vs. K/K+), as verified by X-ray diffraction characterization and first-principles calculations. Owing to its highly stable layered oxide framework, P2-K0.75MNFO2 delivers a high reversible capacity of 110 mA h g−1 at 0.1C and exhibits an outstanding cycle retention of 70% over 200 cycles at both 1C and 10C. In addition, a full cell with P2-K0.75MNFO2 as the cathode and hard carbon as the anode demonstrates long-term cycling stability over 1000 cycles, illustrating the feasibility of a safe and practical KIB system.

Li-rich layered oxide materials are considered promising candidates for high-capacity cathodes for battery applications and improving the reversibility of the anionic redox reaction is the key to exploiting the full capacity of these materials. However, permanent structural change of the electrode occurring upon electrochemical cycling results in capacity and voltage decay. In view of these factors, Ti

This study investigated differences in main purposes of leisure activities, leisure constraints, and the quality of life among segmented clusters based on leisure condition index, leisure resource index, and leisure attitude index utilizing Korean Better Leisure Index (K-BLI). Characteristics of each cluster were aggregated for profiling using data from the ⎡National Leisure Activity Survey 2019⎦ in Korea. Results of this study provide room for debate and response regarding leisure experience and sustainability of recreation service in local community based on characteristics of each cluster. This study semanticized adults living in Gyeonggi-do having the highest population density in Korea by conducting K-means clustering. This study segmented subjects into three clusters. Characteristics of each cluster were determined and t-test was conducted to determine associations among the main purpose of leisure activities, leisure constraints, and quality of life. As a result, adults living in Gyeonggi-do were divided into “dissatisfaction with leisure resource”, “dissatisfaction with the quality of life”, and “sensitive to the leisure constraints” clusters. Their desire for improvement for quality of life and leisure activity were definitely clear. This means that results of this study through segmentation based on leisure index are meaningful as baseline data to suggest an actual policy plan.