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•Graphitic nanofibers (BCNFs) were produced from biogas by catalytic decomposition.•The electrochemical intercalation of PF6− anions into BCNF cathodes is investigated.•BCNF ...electrochemical performance as cathodes depends on their graphitic structure.•BCNF graphitic domain height determines the scope of PF6− anions intercalation.
The electrochemical intercalation of PF6− anions into graphitic nanomaterials of renewable origin with different degrees of structural order to be subsequently used as cathodes for sodium dual-ion batteries is herein investigated for the first time. Overall, the electrochemical performance of the biogas-derived carbon nanofibers depends on their graphitic structure, specifically on crystallite height which was found to be the determining parameter for the scope of electrochemical intercalation of PF6− anions into these nanomaterials.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The electrochemical performance of novel nano-silicon/biogas-derived carbon nanofibers composites (nSi/BCNFs) as anodes in lithium-ion batteries was investigated, focusing on composition and ...galvanostatic cycling conditions. The optimization of these variables contributes to reduce the stress associated with silicon lithiation/delithiation by accommodating/controlling the volume changes, thus preventing anode degradation and therefore improving its performance regarding capacity and stability. Specific capacities up to 520 mAh g−1 with coulombic efficiency > 95% and 94% of capacity retention are achieved for nSi/BCNFs anodes at electric current density of 100/200 mA g−1 and low cutoff voltage of 80 mV. Among the BCNFs, those no-graphitized with fishbone microstructure, which have a great number of active sites to interact with nSi particles, are the best carbon matrices. Specifically, a nSi:BCNFs 1:1 weight ratio in the composite is the optimal, since it allows a compromise between a suitable specific capacity, which is higher than that of graphitic materials currently commercialized for LIBs, and an acceptable capacity retention along cycling. Low cutoff voltage in the 80–100 mV range is the most suitable for the cycling of nSi/BCNFs anodes because it avoids formation of the highest lithiated phase (Li15Si4) and therefore the complete silicon lithiation, which leads to electrode damage.
Carbon xerogel with different mean pore sizes (10, 50, 100, 500 nm) but analogous structure, chemical composition, surface area, and microporosity, which are produced by an energy-effective ...microwave-based process, and activated carbon xerogels (100 nm-pore size) with higher microporosity were investigated as anodes for sodium dual-ion batteries. The objective of this study was to optimize the material textural properties for this specific application to be further matched with a carbon xerogel-based cathode in a full battery configuration. To this end, the role of these properties was evaluated, specifically the pore size and the microporosity since the storage of the Na+ ions in these carbon xerogels was demostrated to occur mainly by a pseudocapacitive mechanism based on adsorption on surface, defects (i.e. microporosity) and pores. The balance between the pore size and the associated external surface area of the carbon xerogels was a determining factor for their anodic performance. In this context, a material pore size of ∼ 100 nm and an associated external surface area of ∼ 100 m2 g−1 was the optimum balance. For a given material pore size, the increase of the microporosity by physical activation improved the anode capacity as well as the cycling stability. However, the development of the microporosity in relation to the external surface area must be optimized to avoid an undesirable increase in the first cycle irreversible capacity. Overall, the physically activated carbon xerogel with a pore size of 100 nm, a micropore volume of 0.47 cm3 g−1 and an external surface of 123 m2 g−1 was the most suitable active anode material for sodium dual-ion batteries. This material provided a specific discharge capacity of ∼ 154 mAh g−1 after 300 discharge/charge cycles with excellent cycling stability and coulombic efficiency.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The intercalation of PF6− anions in graphite from various sodium salt-based electrolytes with organic carbonate mixtures as solvents is investigated. The purpose was to optimize the electrochemical ...performance of the graphite as cathode in terms of specific capacity, capacity stability, and coulombic efficiency to be coupled in the future with a hard carbon-based anode in a full sodium dual-ion battery. To this end, a detailed study was made of the influence of applied current density, upper cut-off voltage (UCOV), and electrolyte—in terms of both salt concentration and solvent mixture—on the intercalation/de-intercalation of PF6− anions in the graphite cathode. Low (37.2 mA g−1) and high (372.0 mA g−1) currents, UCOVs from 4.8 to 5.2 V, electrolytes with NaPF6 salt concentrations in the range of 0.2–1.2M and EC:DEC, EC:DMC and EC:EMC solvent mixtures were studied. The best graphite cathode performance was attained in 1.2MNaPF6/EC:EMC electrolyte at the highest current density of 372.0 mA g−1 and for the potential range between 2.9 and 5.0 V vs. Na/Na+. In these conditions, a discharge capacity of 79 mAh g−1 after 1000 cycles with a coulombic efficiency of 99 % and a remarkable capacity retention throughout cycling were determined.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Carbon xerogels (CXs) with the same chemical composition and BET surface area but different pore sizes (10–200 nm), which had been easily produced in large amounts via a cost-effective ...microwave-based process, are investigated as anodes for sodium-ion batteries (SIBs). The role of textural properties of CXs in the process of sodium ions storage was evaluated. The most suitable anode for SIBs was CX-100 with a pore size of 100 nm, the largest micropore volume and the lowest external surface area (Sext), which gives an idea of the most accessible surface of the material, along with relatively high open porosity. Larger pore sizes facilitate electrolyte penetration, thus improving Na+ ions diffusion inside the electrode, while microporosity is crucial in increasing electrode capacity since Na+ ions storage on CXs is mainly due to absorption on the surface and in structural defects (i.e., microporosity). Moreover, lowering Sext leads to a decrease in the Na+ ions used in the formation of the SEI layer and irreversibly absorbed during initial cycles, therefore improving electrode performance. In summary, an optimal combination of textural properties, including pore structure and Sext, should be considered in order to effectively design CXs for SIBs.
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•CXs produced by a microwave-based process are investigated as anodes for SIBs.•The role of CXs textural properties in the process of Na+ ions storage is studied.•Storage of Na+ ions is mainly due to absorption on surface and structural defects.•Large Vmicro and small Sext are crucial to improve capacity of CX-based electrodes.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Silicon/carbon composites are synthesized using a simple and scalable approach.•The composite with 30 wt.% of silicon presents specific discharge capacity as high as 917 mAh g−1 after 200 ...cycles.•The composite with 30 wt.% of silicon presents excellent stability in the long-term.
Silicon-based anodes are widely studied as an alternative to graphite anodes for lithium-ion batteries. Nevertheless, their practical application is mainly limited by the huge volume change that silicon particles undergo due to alloying and de-alloying with lithium ions during discharge/charge processes, which result in cracks and electrode degradation. In the present study, porous silicon-carbon composites are investigated as anode materials for next-generation lithium-ion batteries. These composites are prepared by a cost-effective, easily-scalable method based on a microwave assisted approach for the carbon matrix, followed by dispersion of the silicon in 2-propanol. The electrochemical behavior of the Si/C composites with different proportions of silicon is evaluated in terms of alloying and de-alloying mechanisms of lithium ions, battery reversible capacity, irreversible capacity in the first cycle, retention of capacity along cycling, and cycle efficiency. The composite with 30 wt.% of silicon presents specific discharge capacity as high as 917 mAh g−1 after 200 cycles and excellent stability in the long-term at high current density, which makes it a promising candidate for the lithium-ion battery market.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Abstract
A detailed study of the intercalation/de‐intercalation mechanisms of PF
6
−
anions in a graphite cathode of sodium dual‐ion batteries is carried out by cyclic voltammetry. The influence of ...the continuous anion intercalation/de‐intercalation on the graphite structure is investigated by ex‐situ XRD after cycling. It was concluded that the intercalation/de‐intercalation occurs through a combination of diffusion‐controlled and pseudocapacitive mechanisms. Initially, the contribution of the diffusion‐controlled is significant, specifically at the highest voltage and at the lowest scan rates which agrees with the slow kinetic of this mechanism and its usual prevalence in carbon materials with a graphitic structure. However, the continuous anion intercalation/de‐intercalation causes some deterioration of the graphite structural order, even from the initial cycles, as it was demonstrated by the evolution of the crystalline parameters, interlayer spacing,
d
002
, and crystallite size,
L
c
. This deterioration hinders the diffusion‐controlled anion intercalation/de‐intercalation and, as a consequence, the pseudocapacitive becomes the main mechanism along cycling. Therefore, since graphite is capable of intercalating PF
6
−
anions at high voltages through a capacitive mechanism, with its consequent rapid kinetics, this carbon material is an excellent candidate for using as cathode in high power sodium dual‐ion batteries, in which, kinetically fast mechanisms are required.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The measured reversible capacity of the single layer graphene electrode (SLG/Cu) in sodium-ion batteries is mostly due to the electrochemical response of the copper substrate.
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•Single ...layer graphene (SLG) grown on copper foil is investigated as anode for sodium-ion batteries.•The amount of Na+ ions adsorbed/desorbed reversibly per surface area is very modest (<20μAhcm−2).•The reversible capacity of SLG is mostly due to the electrochemical response of copper substrate.•The results agree with calculations showing that Na+ ions adsorption on SLG is energetically unfavourable.
In an attempt to find an adequate carbon material to achieve a successful reversible adsorption of Na+ ions, single layer graphene, is experimentally investigated in this work, for the first time, as anode for sodium-ion batteries. To this end, single layer graphene that was grown on copper foil by chemical vapor deposition was subjected to extended galvanostatic cycling and to cyclic voltammetry in the potential range of 0-2.8V versus Na/Na+. Regardless of the current density and electrolyte formulation used, the amount of Na+ ions adsorbed/desorbed reversibly per surface area (specific reversible cell capacity) was very modest and comparable to that obtained with bare copper electrodes of reference, thus suggesting that the reversible capacity of the single layer graphene electrode is mostly due to the electrochemical response of the copper substrate. These experimental results clearly agree with recent theoretical calculations showing that the adsorption of Na+ ions on the surface of single layer graphene is energetically unfavourable unless that surface includes significant defects density.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
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•Seven water-soluble hydrocolloids are tested as binders for graphite anodes in LIBs.•All hydrocolloids meet the thermal and electrochemical stability required.•Optimal binder ...concentration of 5wt% is found for graphite/hydrocolloid electrodes.•Four of them show cycling performances comparable to graphite/PVDF electrode.
A series of seven different hydrocolloids are tested as water-soluble binders for synthetic graphite (SG)-based electrodes of lithium-ion batteries (LIBs) and compared with the standard poly(vinylidene difluoride) (PVDF) binder. The hydrocolloids selected are sodium carboxymethyl cellulose (Na-CMC), sodium alginate (Na-Alg), gum arabic (GA), xanthan gum (XG), guar gam (GG), agar-agar (AA) and carrageenan (CAR), the latter three with no precedents in the literature. They all show thermal and electrochemical stability under the experimental conditions employed. For SG/hydrocolloid electrodes, binder concentrations of 5wt% are found to be optimal, providing outstanding electrochemical performances for electrodes with Na-Alg Na-CMC, XG and GG in galvanostatic cycling experiments at constant (C/10, with C=372mAg−1) and variable (fromC/10 to 2C) current rates, which are comparable, or even superior to those of SG/PVDF electrodes with higher binder content (8wt%). In contrast, SG/GA, SG/CAR and SG/AA electrodes show poorer electrochemical performances, most likely owing to the low adhesion capacity of the binder (GA and CAR), or the formation of films covering the SG particles (CAR and AA).
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The electrochemical performance as potential anodes for lithium-ion batteries of graphitized biogas-derived carbon nanofibers (BCNFs) is investigated by galvanostatic cycling versus Li/Li+ at ...different electrical current densities. These graphitic nanomaterials have been prepared by high temperature treatment of carbon nanofibers produced in the catalytic decomposition of biogas. At low current density, they deliver specific capacities comparable to that of oil-derived micrometric graphite, the capacity retention values being mostly in the range 70-80% and cycling efficiency ∼ 100%. A clear tendency of the anode capacity to increase alongside the BCNFs crystal thickness was observed. Besides the degree of graphitic tri-dimensional structural order, the presence of loops between the adjacent edges planes on the graphene layers, the mesopore volume and the active surface area of the graphitized BCNFs were found to influence on battery reversible capacity, capacity retention along cycling and irreversible capacity. Furthermore, provided that the development of the crystalline structure is comparable, the graphitized BCNFs studied show better electrochemical rate performance than micrometric graphite. Therefore, this result can be associated with the nanometric particle size as well as the larger surface area of the BCNFs which, respectively, reduces the diffusion time of the lithium ions for the intercalation/de-intercalation processes, i.e. faster charge-discharge rate, and increases the contact area at the anode active material/electrolyte interface which may improve the Li+ ions access, i.e. charge transfer reaction.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
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