Electrochemical Storage Behavior Research Articles

Production and characterization of activated carbon foams with various activation agents for electrochemical double layer capacitors (EDLCs) applications

Sucrose-based activated carbons were obtained by carbon foams with sugar and cobalt (II) nitrate as precursors, followed by using different chemical activation agents. The effect of Co(NO3)2 concentration, the carbonization temperature and the activation agent on the surface chemistry, porosity were investigated. Textural characterization and electrochemical tests were performed on the activated carbon samples (CF). The results showed that the activated carbon produced by H2SO4 and KOH at 800°C had a surface area of 691 m2/g and 1125 m2/g, 89% and 80% of the sample pore structure was microporous, and specific capacitance of 8.4 F/g and 162.2 F/g at a constant current density of 250 mA/g, respectively. K2CO3-activated carbon had 918 m2/g surface area and 63% of the sample pore structure with microporous and 1.4 F/g specific capacitance, H3PO4-activated carbon and ZnCl2-activated carbon had 1833 m2/g and 1597 m2/g surface area, 53% mesoporous and 50% mesoporous, 222.4 F/g and 149.9 F/g specific capacitance respectively. The most promosing result was observed in the electrochemical storage behavior of the carbon materials with hierarchical pore structure activated with H3PO4 is associated with increasing defect zones at the edges of micro- and mesoporous morphology, resulting in a higher surface area and increased conductivity of the material.

Electrochemical Storage Behavior of a High-Capacity Mg-Doped P2-Type Na2/3Fe1-yMnyO2 Cathode Material Synthesized by a Sol-Gel Method.

Grid-scale energy storage applications can benefit from rechargeable sodium-ion batteries. As a potential material for making non-cobalt, nickel-free, cost-effective cathodes, earth-abundant Na2/3Fe1/2Mn1/2O2 is of particular interest. However, Mn3+ ions are particularly susceptible to the Jahn-Teller effect, which can lead to an unstable structure and continuous capacity degradation. Modifying the crystal structure by aliovalent doping is considered an effective strategy to alleviate the Jahn-Teller effect. Using a sol-gel synthesis route followed by heat treatment, we succeeded in preparing an Mg-doped Na2/3Fe1-yMnyO2 cathode. Its electrochemical properties and charge compensation mechanism were then studied using synchrotron-based X-ray absorption spectroscopy and in situ X-ray diffraction techniques. The results revealed that Mg doping reduced the number of Mn3+ Jahn-Teller centers and alleviated high voltage phase transition. However, Mg doping was unable to suppress the P2-P'2 phase transition at a low voltage discharge. An initial discharge capacity of about 196 mAh g-1 was obtained at a current density of 20 mAh g-1, and 60% of rate capability was maintained at a current density of 200 mAh g-1 in a voltage range of 1.5-4.3 V. This study will greatly contribute to the ongoing search for advanced and efficient cathodes from earth-abundant elements for rechargeable sodium-ion batteries operable at room temperature.

Novel porous CoS1.097@carbon nanofibers as flexible and binder-free anode material for sodium-ion batteries

Transition metal sulfides (TMSs) have received numerous attention as anode materials for sodium-ion batteries because of the high theoretical capacity. So far, the Na-storage performance of TMSs is still unsatisfactory due to the structural degeneration that induced by the volume change upon redox process. Herein, a novel flexible and binder-free anode material of porous CoS1.097@carbon nanofibers was facilely constructed by means of the electrospinning, carbonization and sulfidation processes. The porous CoS1.097@carbon nanofibers display unique structure with CoS1.097 nanoparticles confined into porous N-doped carbon nanofibers, and can provide sufficient active sites, high electrical conductivity, reduced ion diffusion distance, abundant ion migration pathways, desirable voids for alleviating the volume variation, and rigid structural stability for efficient Na-storage. In consequence, the flexible and binder-free electrode material delivers high initial discharge capacity, enhanced rate capability and long-term cycling life. Besides, intrinsic diffusion and electrochemical storage behavior of Na+ ions were emphatically disclosed. This work paves a facile route for the synthesis of flexible and binder-free TMSs-based anode materials, promoting the practical application of wearable sodium-ion batteries.

SiCO Ceramics as Storage Materials for Alkali Metals/Ions: Insights on Structure Moieties from Solid-State NMR and DFT Calculations.

Polymer-derived silicon oxycarbide ceramics (SiCO) have been considered as potential anode materials for lithium- and sodium-ion batteries. To understand their electrochemical storage behavior, detailed insights into structural sites present in SiCO are required. In this work, the study of local structures in SiCO ceramics containing different amounts of carbon is presented. 13 C and 29 Si solid-state MAS NMR spectroscopy combined with DFT calculations, atomistic modeling, and EPR investigations, suggest significant changes in the local structures of SiCO ceramics even by small changes in the material composition. The provided findings on SiCO structures will contribute to the research field of polymer-derived ceramics, especially to understand electrochemical storage processes of alkali metal/ions such as Na/Na+ inside such networks in the future.

Electrochemical storage behavior of NiCo 2 O 4 nanoparticles anode with structural and morphological evolution in lithium‐ion and sodium‐ion batteries

Electrochemical storage behavior of <scp> NiCo ₂ O ₄ </scp> nanoparticles anode with structural and morphological evolution in lithium‐ion and sodium‐ion batteries

MnOx thin film based electrodes: Role of surface point defects and structure towards extreme enhancement in specific capacitance

Manganese oxide (MnOx) is a low cost and environment-friendly electrode material for supercapacitors. Although most efforts have been devoted to increase the surface area of this material, the role of surface defects in different MnOx polymorphs towards improvement of its capacitance remains to be thoroughly investigated. In this paper, the results from electrodeposition of mesoporous MnOx thin film electrodes and the effect of rapid thermal annealing (RTA) on their electrochemical storage behavior are presented and discussed. X-ray photoelectron spectroscopy (XPS) analyses showed an increase of the Mn2+/Mn3+ ratio as well as hydroxyl group defects on the surface of the annealed electrodes. The as-deposited MnOx did not manifest any capacitance behavior in 1.0 M Na2SO4 electrolyte solution. However, after RTA treatment, the specific capacitance was tremendously enhanced. An areal capacitance as high as 110 mF cm−2 at 5 mV s−1 was recorded in 1.0 M Na2SO4 electrolyte with a capacitance retention of 74% after 5000 charge-discharge cycles. Furthermore, the RTA treatment of electrodes significantly decreased the charge transfer resistance value from 0.678 × 106 Ω for the pristine MnOx electrode to 39.13 Ω for the treated one. Based on structural and surface chemistry evolution of the MnO2 films after annealing, the electrochemical storage behavior of annealed MnOx is discussed.

Evidence for Fast Lithium-Ion Diffusion and Charge-Transfer Reactions in Amorphous TiO x Nanotubes: Insights for High-Rate Electrochemical Energy Storage.

The charge-storage kinetics of amorphous TiO x nanotube electrodes formed by anodizing three-dimensional porous Ti scaffolds are reported. The resultant electrodes demonstrated not only superior storage capacities and rate capability to anatase TiO x nanotube electrodes but also improved areal capacities (324 μAh cm-2 at 50 μA cm-2 and 182 μAh cm-2 at 5 mA cm-2) and cycling stability (over 2000 cycles) over previously reported TiO x nanotube electrodes using planar current collectors. Amorphous TiO x exhibits very different electrochemical storage behavior from its anatase counterpart as the majority of its storage capacity can be attributed to capacitive-like processes with more than 74 and 95% relative contributions being attained at 0.05 and 1 mV s-1, respectively. The kinetic analysis revealed that the insertion/extraction process of Li+ in amorphous TiO x is significantly faster than in anatase structure and controlled by both solid-state diffusion and interfacial charge-transfer kinetics. It is concluded that the large capacitive contribution in amorphous TiO x originates from its highly defective and loosely packed structure and lack of long-range ordering, which facilitate not only a significantly faster Li+ diffusion process (diffusion coefficients of 2 × 10-14 to 3 × 10-13 cm2 s-1) but also more facile interfacial charge-transfer kinetics than anatase TiO x.

Rapid and durable electrochemical storage behavior enabled by V4Nb18O55 beaded nanofibers: a joint theoretical and experimental study

V4Nb18O55 beaded nanofibers demonstrated highly reversible storage of lithium ions and transportation performance via a joint theoretical and experimental study.

MnO2-Vertical graphene nanosheets composite electrodes for energy storage devices

The vertical graphene nanosheets (VGNs) have attracted considerable attention for energy storage application due to their inherent properties such as morphology, large surface area, high electrical conductivity and three dimensional (3D) open network structures. Here, we report on the growth of VGNs using electron cyclotron resonance - chemical vapor deposition and its electrochemical storage behavior. Further, a near homogeneous dispersion of MnO2 is coated over VGNs by dip casting to enhance the effective capacitance. Electrochemical charge storage behavior of VGNs and MnO2/VGNs composites are investigated using cyclic voltametry and electrochemical impedance spectroscopy (EIS) and also the results are compared. The MnO2/VGNs composites exhibit the highest areal capacitance of 5.6 mF/cm2, which is 110 times higher than that of VGNs (51.95 μF/cm2) at a scan rate of 50 mV/s. The enhanced capacitance is due to highly conductive 3D network of VGNs which provide fast electron and ion transport and also a large pseudo-capacitance from MnO2 coating. The EIS results are analyzed with equivalent circuit model which reveals the charge storage mechanism in the materials. Scanning electron microscopy and Raman spectroscopy are also used to understand the morphology and structure – property correlations of the films. These results demonstrate clearly that the MnO2/VGNs composite is a potential candidate for energy storage applications.

Hierarchical MoSe2 Nanosheets/Reduced Graphene Oxide Composites as Anodes for Lithium‐Ion and Sodium‐Ion Batteries with Enhanced Electrochemical Performance

AbstractThe preparation and electrochemical storage behavior of hierarchical MoSe2/reduced graphene oxide (rGO) composites were studied. The preparation was achieved by a facile hydrothermal route. The results show that MoSe2 has a high capacity for lithium ion and sodium ion storage and that the incorporation of rGO has further improved the electrochemical property of MoSe2 effectively. As anode materials for lithium‐ion and sodium‐ion batteries, the MoSe2/rGO composites demonstrate excellent rate performance and cycling stability of 917 mA h g−1 after 100 cycles for Li+ storage and 430 mA h g−1 after 200 cycles for Na+ storage at a current density of 0.5 A g−1, which is attributed to the robust hierarchical structure and the synergistic effects between MoSe2 nanosheets and rGO. Therefore, the electrochemical evaluations suggest that the obtained hierarchical structure MoSe2/rGO composites hold great potential as anode materials for lithium‐ion and sodium‐ion batteries.

Single‐Layered Ultrasmall Nanoplates of MoS2 Embedded in Carbon Nanofibers with Excellent Electrochemical Performance for Lithium and Sodium Storage

The preparation and electrochemical storage behavior of MoS2 nanodots--more precisely single-layered ultrasmall nanoplates--embedded in carbon nanowires has been studied. The preparation is achieved by an electrospinning process that can be easily scaled up. The rate performance and cycling stability of both lithium and sodium storage were found to be outstanding. The storage behavior is, moreover, highly exciting from a fundamental point of view, as the differences between the usual storage modes--insertion, conversion, interfacial storage--are beneficially blurred. The restriction to ultrasmall reaction domains allows for an almost diffusion-less and nucleation-free "conversion", thereby resulting in a high capacity and a remarkable cycling performance.

Single‐Layered Ultrasmall Nanoplates of MoS2 Embedded in Carbon Nanofibers with Excellent Electrochemical Performance for Lithium and Sodium Storage

AbstractThe preparation and electrochemical storage behavior of MoS2 nanodots—more precisely single‐layered ultrasmall nanoplates—embedded in carbon nanowires has been studied. The preparation is achieved by an electrospinning process that can be easily scaled up. The rate performance and cycling stability of both lithium and sodium storage were found to be outstanding. The storage behavior is, moreover, highly exciting from a fundamental point of view, as the differences between the usual storage modes—insertion, conversion, interfacial storage—are beneficially blurred. The restriction to ultrasmall reaction domains allows for an almost diffusion‐less and nucleation‐free “conversion”, thereby resulting in a high capacity and a remarkable cycling performance.

Storage performance of LiFePO4nanoplates

The morphology of electrode materials is addressed as a key factor controlling rapid lithium storage in anisotropic systems such as LiFePO4. In view of this, we have synthesized nanoplates of LiFePO4 with a uniform coating of a 5 nm thick amorphous carbon layer by the solvothermal method and investigated their electrochemical storage behavior. The obtained nanoplates are well characterized by XRPD, SEM, HRTEM and XPS techniques. The thickness along the b-axis is found to be 30–40 nm; such a morphology favors short diffusion lengths for Li+ ions, while the external conductive carbon coating provides connectivity for facile electron diffusion, resulting in high rate performances. Increase in the size of the nanoplates results in poor lithium storage performance. The storage performance of nanoplates is compared with that of mesoporous nanoparticles of LiFePO4 with non-uniform carbon coating. This paper thus describes the advantages of thinner nanoplates for high rate storage performances of battery electrode materials.