Hard carbon is the most promising anode material for sodium‐ion batteries and potassium‐ion batteries owing to its high stability, widespread availability, low‐cost, and excellent performance. ...Understanding the carrier‐ion storage mechanism is a prerequisite for developing high‐performance electrode materials; however, the underlying ion storage mechanism in hard carbon has been a topic of debate because of its complex structure. Herein, it is demonstrated that the Li+‐, Na+‐, and K+‐ion storage mechanisms in hard carbon are based on the adsorption of ions on the surface of active sites (e.g., defects, edges, and residual heteroatoms) in the sloping voltage region, followed by intercalation into the graphitic layers in the low‐voltage plateau region. At a low current density of 3 mA g–1, the graphitic layers of hard carbon are unlocked to permit Li+‐ion intercalation, resulting in a plateau region in the lithium‐ion batteries. To gain insights into the ion storage mechanism, experimental observations including various ex situ techniques, a constant‐current constant‐voltage method, and diffusivity measurements are correlated with the theoretical estimation of changes in carbon structures and insertion voltages during ion insertion obtained using the density functional theory.
Li+, Na+, and K+ ions have identical storage mechanisms in hard carbon–adsorption followed by intercalation. The sloping voltage capacity is attributed to the adsorption of the carrier ions on defect sites, edge sites, and the surface of micropores, whereas the low‐voltage plateau capacity is caused by the intercalation of the carrier ions into graphitic layers.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
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•Ash-removal techniques were tested to enhance Na+ uptake capacity in hard carbon (HC).•Pre-acid treatment removed some hemicellulose and pectin fractions from raw cocoa pod husk ...(CPH).•HC from acid-treated CPH delivered 317mAhg−1 with ICE of 87%.
Biomass is a promising precursor for producing high-performance hard carbon as an anode for sodium-ion batteries (SIBs) because of its high low-voltage plateau capacity. However, the effect of residual ash in biomass on the electrochemical performance of hard carbons has rarely been investigated. This work describes an effective ash-removal approach as a critical step for preparing high-performance anodes for SIBs. A strong correlation between the ash removal techniques with structural and electrochemical properties of hard carbon was revealed. By examining various ash-removal techniques prior to carbonization and after carbonization using aqueous acid, neutral, and alkaline solutions, it was demonstrated that the removal of ash from raw cocoa pod husk (CPH) using aqueous acid and subsequent carbonization at 1300°C can produce hard carbon with high Na+ ion uptake in the low-voltage plateau region. During the acid pretreatment, ash and some hemicellulose fractions were removed, and carbonization of the acid-treated CPH resulted in hard carbon with a high degree of graphitization and reduced surface area. When tested as an anode in SIBs, the hard carbon produced from the acid-treated CPH exhibited an exceptionally high capacity of 317mAhg−1 and high plateau capacity of 244mAhg−1 at 0.05Ag−1, with a high initial Coulombic efficiency of 87%. At a high current density of 250mAg−1, a high capacity of 134mAhg−1 was maintained after 800 cycles. Post-treatment of hard carbon did not enhance the electrochemical performance. The physicochemical and electrochemical properties of hard carbons produced with the various pre- and post-treatment techniques were presented.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Hard carbon is a promising anode material for sodium ion batteries (NIBs). In this study, a two-step carbonization approach is developed to enhance the electrochemical performance of lignocellulose ...biomass-derived hard carbon. The first step comprises slow low-temperature pyrolysis of fir wood that produces an amorphous carbon in which hexagonal planes are embedded in the amorphous carbon region to some extent. The second step comprises high-temperature carbonization at 1300 °C, which yields a hard carbon with a high degree of graphitization, an increased layer-plane length, and a low micropore volume. Two-step carbonized hard carbon delivers a large reversible capacity of 276 mAh g−1 at 50 mA g−1 after 100 cycles and high rate capacities of 108 mAh g−1 at 1.0 A g−1 and 76.3 mAh g−1 at 2.5 A g−1. The low-voltage plateau capacity below 0.1 V is 194 mAh g−1. The results of these experiments indicate that the exceptional electrochemical performance of two-step carbonized hard carbon arises from the effective suppression of micropore formation and a good balance between the degree of graphitization and number of defect sites. High-voltage adsorption of Na+ ions in micropores inhibits Na+-ion diffusion into the graphitic region of micropore-enriched hard carbon.
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•Two-step carbonization of wood was developed to enhance low-voltage plateau capacity.•Low-voltage plateau capacity below 0.1 V of 194 mAh g−1 were achieved.•Stable capacity of 276 mAh g−1 for 100 cycles was achieved as an anode in NIBs.•Na+ ion adsorption in micropores inhibited Na+-ion diffusion into graphitic region.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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•High-temperature carbonization with low-level heteroatom doping was developed.•P-doped carbon exhibited enhanced low-voltage plateau capacity of 223 mAh g−1 in SIBs.•High reversible ...capacity of 328 mAh g−1 with high ICE of 72% was achieved in SIBs.•As an anode in KIBs, high reversible capacity of 302 mAh g−1 was achieved.
Hard carbon is one of most promising anode materials used in sodium-ion batteries (SIBs) because of its high low-voltage plateau capacity. Heteroatom doping into the carbon structure is considered an effective method to enhance the Na+-ion uptake. However, heteroatom doping is not utilized to increase the low-voltage plateau capacity because the carbonization temperatures are limited to low values (600–1100 °C). In addition, the formation of excess defect sites, which is caused by heteroatom doping leads to lower initial Coulombic efficiency (ICE). Herein, to increase the low-voltage plateau capacity and to maintain high ICE, combination of high-temperature carbonization and low-level heteroatom doping is investigated. The P-doped hard carbon synthesized at 1300 °C with doping level of 1.1 at.% exhibits enhanced reversible capacity of 328 mAh g−1 at 50 mA g−1, and high ICE of 72% in SIBs. After the P-doping, the low-voltage plateau capacity increases, while the high-voltage sloping capacity does not change significantly. This is attributed to the enlargement of the interlayer spacing between the graphitic layers, which enhances Na+-ion intercalation. The P-doped hard carbon delivers a high reversible capacity of 302 mAh g−1 in potassium-ion batteries (KIBs); this value is 23% larger than that of undoped hard carbon.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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•Hard carbon (HC) with increased low-voltage plateau capacity in NIBs was presented.•Decrease in crystallinity of precursor increased pseudo-graphitic domains in HC.•Increase in the ...pseudo-graphitic domains enhanced low-voltage plateau capacity.•High capacities of 322 and 281 mAh g−1 were achieved in NIB and KIB, respectively.•Low-voltage capacities were 207 and 175 mAh g−1 for NIB and KIB, respectively.
Hard carbon is considered as a promising anode material for sodium-ion batteries (NIBs) and potassium-ion batteries (KIBs) owing to its high low-voltage plateau capacity and excellent long-term stability over several charging cycles. Based on the adsorption–intercalation mechanism, the low-voltage plateau capacity originates from the intercalation of carrier ions between misaligned graphene layers. In this study, the intercalation sites in cellulose-derived hard carbon were controlled by varying the degree of crystallinity of cellulose. The hard carbon synthesized from cellulose with an optimum degree of crystallinity delivered high specific capacities of 322 and 281 mAh g−1 in NIB and KIB, respectively. The increased total capacity emerges predominantly from the low-voltage plateau capacities (207 and 175 mAh g−1 for NIB and KIB, respectively) rather than the high-voltage sloping capacities. Based on the correlation analysis between the type of intercalation sites and low-voltage plateau capacity, pseudo-graphitic domains with interlayer spacings between 0.36 and 0.40 nm are responsible for the low-voltage plateau capacity in NIBs and KIBs. The new insight into the increased percentage of pseudo-graphitic regions in hard carbon could provide a rational guide for designing high-performance anodes in NIBs and KIBs for practical use.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Although many studies have demonstrated the excellent potential of hard carbon as an anode in sodium ion batteries, the contribution of its active sites to the capacities of the sloping and plateau ...voltage regions is not yet clear. Herein, systematical investigation of the relationship between the active sites and sodium ion (Na+) storage in the sloping and plateau voltage regions was presented. In light of the physicochemical properties of the lignin-derived hard carbon (graphitization degree, interlayer spacing, micropore size distribution, and specific surface area), the results of Na+ ion diffusivity, and the change in these properties during Na+ ion insertion/extraction (as characterized by ex situ techniques), new mechanistic insights into Na+ ion storage were proposed. At the beginning of the sodiation process, Na+ ions were adsorbed on defect/edge sites; then partial micropore filling occurred in the sloping region above 0.1 V. In the plateau region below 0.1 V, Na+ ions were intercalated in the graphitic layers, and further adsorption in the micropores occurred near the cutoff potential. Furthermore, sodium clustering occurred below 0.1 V owing to the high concentration of Na+ ions in the micropores.
Proposed new sodium ion storage mechanism in hard carbon derived from lignin. At the beginning of the sodiation process, Na+ ions are adsorbed on defect/edge sites; then partial micropore filling occurs in the sloping region above 0.1 V. In the plateau region below 0.1 V, Na+ ions are intercalated in the graphitic layers, and further adsorption in the micropores occurs near the cutoff potential. Furthermore, sodium clustering occurs below 0.1 V owing to the high concentration of Na+ ions in micropores. Display omitted
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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•SiOC with a high reversible capacity of 234 mAh g−1 in NIB was presented.•High plateau capacity below 0.1 V of 121 mAh g−1 was achieved.•Change of flow gas from H2/Ar to N2 decreased ...the inactive SiC and Cfree phases.•Utilization of C-rich precursor reduced the amount of inactive SiO2 phase.•A high capacity of 299 mAh g−1 was achieved in the CCCV test.
Silicon oxycarbides (SiOCs) are considered promising sodium-ion battery anode materials. However, the total and low-voltage plateau capacities of SiOCs are low (below 200 and 95 mAh g−1, respectively), which hinders the manufacturing of high-density electrodes. Herein a new strategy for improving the electrochemical performance of SiOCs was proposed by considering the Na+ ion storage mechanisms in SiOCs. High-capacity SiOCs were synthesized by increasing the amount of C- and O-rich SiOxCy phases and reducing the amount of inactive SiO2, SiC, and Cfree phases. The compositions of SiOCs were controlled by adjusting the synthesis conditions (e.g., sweep gas and pyrolysis time) and C content of the SiOC precursors. The use of N2 sweep gas instead of H2/Ar suppressed the formation of SiC and Cfree. In addition, the amount of inactive SiO2 phase in SiOCs was further suppressed using a C-rich precursor. Consequently, the synthesized SiOC, which was enriched with C- and O-rich SiOxCy phases, delivered a high reversible capacity of 234 mAh g−1 at a current density of 25 mA g−1. In constant-current/constant voltage mode, the reversible capacity was further increased to 299 mAh g−1, which was close to the theoretical maximum capacity of 315 mAh g−1. After 140 cycles, the reversible capacity was stabilized to 160 mAh g−1. The initial capacity loss during long-term cycling, which was mostly caused by the progressive decrease in the low-voltage plateau capacities, was attributed to the increase in cell polarization.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Silicon oxycarbides (SiOCs) are considered promising anode materials for sodium-ion batteries. However, the mechanisms of Na+-ion storage in SiOCs are not clear. In this study, the mechanism of ...Na+-ion storage in high-temperature-synthesized SiOCs (1200–1400 °C) is examined. Phase separation of the oxygen (O)-rich and carbon (C)-rich SiO x C y domains of SiOC during synthesis was accompanied by the evolution of micropores, graphitic layers, and a silicon carbide (SiC) phase. The high-temperature-synthesized SiOCs exhibited a large voltage plateau capacity below 0.1 V (45–63% of the total capacity). Ex situ measurements and density functional theory simulations revealed that within the sloping voltage region, Na+-ion uptake occurs mainly in the defects, micropores, C-rich SiO x C y phase, and some O-rich SiO x C y phases. In contrast, in the voltage plateau below 0.1 V, Na+-ion insertion into the O-rich SiO x C y phase and formation of Na-rich Si compounds are the main Na+-ion uptake mechanisms. The generated SiC phase confers excellent long-term cyclability to the high-temperature-synthesized SiO x C y .
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IJS, KILJ, NUK, PNG, UL, UM
In article number 2000283 Sang Kyu Kwak, Jaehoon Kim and co‐workers show that the interlayer spacing of hard carbon decreases after the initial intercalation of a few Li+ ions at the edge of the ...graphene layer, whereas the interlayer spacing is expanded during the initial intercalation of a few Na+ and K+ ions into the graphene layer. The dilated interlayer spacing is beneficial for Na+ and K+‐ion intercalation at relatively higher potentials than is the case with Li+‐ion intercalation.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Phishing Attack Awareness Among College Students Kenneth, Alvin; Hayashi, Bernard Bryan; Lionardi, Jason ...
2023 3rd International Conference on Electronic and Electrical Engineering and Intelligent System (ICE3IS),
2023-Aug.-9
Conference Proceeding
Phishing is a form of cyber-attack that uses social engineering techniques to trick individuals into providing sensitive information or clicking on malicious links, often through email or text ...messages. Social engineering is the psychological manipulation of people into performing actions or disclosing sensitive information. In phishing, attackers use social engineering tactics such as creating a sense of urgency, posing as a trustworthy entity, and creating a sense of familiarity to manipulate the victim into taking the desired action. These attacks can have serious consequences, including financial loss and identity theft. In this research, we used an email phishing technique that asked respondents to change their password on an email account to find out awareness of phishing attacks on college students. The research results show that a small percentage of a certain amount of people are still unaware of phishing attacks and fell into the attacker's trap. Several respondents who are still deceived by social engineering using phishing emails indicate that it is necessary to conduct indoctrination and campaigns to raise the awareness of each student.
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