Obtained Discharge Capacity Research Articles

Trimer Quinoxalines as Organic Cathode Materials for Lithium-Ion Batteries

Due to synthetic ease, high redox potentials, low solubility in polar electrolytes, and good electric conductivity of their semiconducting crystals, discotic quinoxaline trimers (3Q) have been considered as possible candidates for 4 V organic cathodes in lithium-ion batteries. To assess their feasibility as such materials, several 3Q derivatives have been synthesized and tested in half-cells. In voltage limited cycling tests at 1.2–3.9 V vs Li/Li+, the specific discharge capacities of 40–180 mAh g−1 were obtained at a rate of 1 C, and multiple lithiation of 3Q and its derivatives was observed during discharge. However, the obtained discharge capacity was only a fraction of the theoretical capacity expected for reversible six-electron reduction; there was also rapid capacity fade. Our spectroscopic studies indicate the reversible three-electron lithiation at 2 V vs Li/Li+, but suggest instability of more highly discharged states. Our conclusion is that while the 3Q derivatives combine several traits that are desirable in an organic cathode material (including negligible solubility, capacity for multiple charging, and near-100% coulombic efficiency), these materials are still impractical to use.

Synthesis, structural characterization, and electrochemical properties of the Mg and Mn doped-Ni(OH)2 for use as active cathode materials in NiFe batteries

• The β-Ni(OH) 2 is synthesized by co-precipitate followed by hydrothermal treatment. • The β-Ni(OH) 2 is modified with Mg 2+ and Mn 2+ to create a superior cathode material. • Mg 2+ and Mn 2+ dopants improved the specific capacity and stability of Ni-electrode. • Mg 2+ and Mn 2+ dopants suppressed the O 2 evolution side reaction. Ni(OH) 2 is one of the most interesting electrode substances for high-performance nickel–iron batteries owing to its low cost, high specific capacitance, and environmental compatibility. However, the Ni(OH) 2 cathode electrode exhibits poor performance due to (i) competitive reactions such as the oxidation of the active material and oxygen evolution. (ii) the reduced charge acceptance of the Ni(OH) 2 positive electrode is related to a relatively long distance between the Ni(OH) 2 particles and the nearest portion of the substrate. In this study, β-Ni(OH) 2 is used as a starting material. Then, the Ni 2+ in the compound β-Ni(OH) 2 material is partially substituted with Mg 2+ and Mn 2+ , separately, and the performance of the as-prepared materials was optimized and examined. XRD, FTIR, TG-DTA, SEM/EDS, and ICP-OES confirmed the formation of the expected compositions. The Ni 0.95 Mg 0.05 (OH) 2 and Ni 0.9 Mn 0.1 (OH) 2 based-samples were optimal compositions with promising electrochemical activities. The partial substitution of Mg 2+ allowed separation of anodic/cathodic peaks and oxygen evolution. For example, the anodic and cathodic peaks are easier to identify because their potential shifted to more negative potentials. When using three-electrode configurations, the un-doped Ni(OH) 2 electrode discharge capacity showed a reduction of 76% after the 100th cycle. In contrast, the Ni 0.95 Mg 0.05 (OH) 2 and Ni 0.9 Mn 0.1 (OH) 2 electrode demonstrated a reduction of only 15% and 12% in discharge capacities after 100th cycles, respectively. When using a two-electrode configuration, the obtained discharge capacities were 40 mAh/g for the un-doped Ni(OH) 2 electrode, 120 mAh/g for the Ni 0.95 Mg 0.05 (OH) 2 electrode, and 159 mAh/g for the Ni 0.9 Mn 0.1 (OH) 2 electrode with an electrode cycle life of 43.49%, 88.24%, 88.54%, respectively.

Iron-Doped Sodium Vanadium Oxyflurophosphate Cathodes for Sodium-Ion Batteries-Electrochemical Characterization and In Situ Measurements of Heat Generation.

Sodium-ion batteries (NaIBs) are increasingly being envisioned for grid-scale energy-storage systems because of cost advantages. However, implementation of this vision has been challenged by the low-energy densities delivered by most NaIB cathodes. Toward addressing this challenge, the authors report the synthesis and characterization of a new iron-doped Na3Fe0.3V1.7O(PO4)2F2 cathode using a novel facile hydrothermal route. The synthesized material was characterized using scanning electron microscopy, X-ray diffraction, and Mössbauer spectroscopy techniques. The obtained discharge capacity in the half-cell configuration lies from 119 to 125 to 130 mA h/g at C/10 while tested using three different electrolyte formulations, dimethyl carbonate-ethylene carbonate (EC)-propylene carbonate (PC), diethyl carbonate-EC, and EC-PC, respectively. The synthesized cathodes were also evaluated in full-cell configurations, which delivered an initial discharge capacity of 80 mA h/g with NaTi2(PO4)3MWCNT as the anode. Ionic diffusivity and interfacial charge transfer kinetics were also evaluated as a function of temperature and sodium concentration, which revealed that electrochemical rate performances in this material were limited by charge-transfer kinetics. To understand the heat generation mechanism of the Na/Na3Fe0.3V1.7O(PO4)2F2 half-cell during charge and discharge processes, an electrochemical isothermal calorimetry measurement was carried out at different current rates for two different temperatures (25 and 45 °C). The results showed that the amount of heat generated was strongly affected by the operating charge/discharge state, C-rate, and temperature. Overall, this work provides a new synthesis route for the development of iron-doped Na3Fe0.3V1.7O(PO4)2F2-based high-performance sodium cathode materials aimed at providing a viable pathway for the development and deployment of large-scale energy-storage based on sodium battery systems.

Chitosan complements entrapment of silicon inside nitrogen doped carbon to improve and stabilize the capacity of Li-ion batteries

A facile strategy to entrap milled silicon (m-Si) particles using nitrogen-doped-carbon (N-C@m-Si) to overcome the dramatic volume changes in Si during intercalation of lithium ions and to improve its electronic conductivity is reported here. The only natural nitrogen containing biomaterial alkaline polysaccharide, i.e., chitosan, is used as the carbon source. Simple hydrothermal technique followed by a subsequent carbonization process is used to synthesize N-C and N-C@m-Si particles. N-C@m-Si exhibited significantly improved electrochemical performance as compared to bare m-Si, which is confirmed by the obtained discharge capacity of 942.4 mAh g−1 and columbic efficiency of 97% after 50 cycles at 0.1C rate. With regard to the N-C electrodes, the obtained discharge capacity of 485.34 mAh g−1 and columbic efficiency of 99.78%, after 50 cycles at 0.1C rate is superior to the commercial graphite electrodes. The solid electrolyte interphase (SEI) layer that formed over m-Si and N-C@m-Si electrodes is characterized using X-ray photoelectron spectroscopy. Compared to the SEI layer that formed over m-Si electrode after 10 charge-discharge cycles, the N-C@m-Si electrode had a stable lithium fluoride and carbonate species. Brief reaction mechanisms, representing the formation of different species in the SEI layer, is derived to explain its behavior during the electrochemical processes.

LiCoO2/Li7La3Zr2O12 nanocomposite cathodes synthesized via self-assembled block copolymer templates and used in all-solid-state lithium batteries

Nanocomposite cathodes comprising an active cathode material (LiCoO2) and a solid lithium electrolyte (Li7La3Zr2O12) were synthesized by using a self-assembled polystyrene‑b‑poly(4‑vinylpyridine) block copolymer template containing precursors of the active cathode material and solid electrolyte. Calcination at 1023 K was used to remove the block copolymer template and crystallize the active cathode material and solid electrolyte. The molecular weight of the block copolymer template was controlled to optimize the structure of the nanocomposite cathode and maximize capacity. When the nanocomposite cathode that was obtained by using the block copolymer template with the highest molecular weight was used in an all-solid-state lithium battery, the obtained discharge capacity per electrode (98.2 mAh/g) was substantially higher than literature values for other cathodes used in all-solid-state lithium batteries. We conclude that increasing the molecular weight of the block copolymer template allowed for greater dispersion of the precursors and binding of the well-dispersed nanoparticles of active cathode material and solid lithium electrolyte, which promoted the formation of fine conducting paths and an electrochemically effective interface between the active cathode material and solid lithium electrolyte.

Extending the High-Voltage Capacity of LiCoO2 Cathode by Direct Coating of the Composite Electrode with Li2CO3 via Magnetron Sputtering

Surface coating of composite electrode has recently received increasing attention and has been demonstrated to be effective in enhancing the electrochemical performance of lithium ion battery (LIB) materials. In this work, an electronic-insulating but ionic-conductive lithium carbonate (Li2CO3) is rationally selected as the unique coating material for commercial LiCoO2 (LCO) cathode. Li2CO3 is a well-known constitute in conventional solid electrolyte interface (SEI) layer, which can electrochemically protect the electrode. The carbonate coating layer is deposited on LCO composite electrodes via a facial magnetron sputtering approach. The sputtered Li2CO3 layer serves as an artificial SEI layer between the active material and electrolyte and can impede the formation of the primary SEI layer, which will permanently consume Li+ and reduce the reversible capacity of the electrode. After a 10 min Li2CO3 coating, the capacity retention of the composite electrode is improved from 64.4% to 87.8% when cycled at room temperature in the potential range of 3.0–4.5 V vs Li/Li+ for 60 cycles. The obtained discharge capacity is extended to 161 mAh g–1, which is 36% higher than the uncoated one (118 mAh g–1). When further increasing the charging potential up to 4.7 V, or elevating the operation temperature to 55 °C, the Li2CO3-coated LCO electrodes still display remarkably improved cycling stability.

A High Rate Lithium-Rich Layered MNC Cathode with Low Capacity Fade for Li-Ion Batteries

We report a new synthesis method, termed self-sustaining combustion reaction, that resulted in a lithium-rich MNC (LLMNC) cathode material with high rate capability and excellent capacity maintenance during cycling compared to the lithium-rich metal oxide cathode materials previously reported in the literature ( 1-4 ). This porous, sponge-like composite metal oxide of the composition, 0.5Li2MnO3. 0.5LiMn0.5Ni0.35Co0.15O2, was characterized by means of its X-ray diffraction (XRD) pattern, FESEM (Field Emission Scanning Electron Microscopy) images and electrochemical data. The interconnected pore structure of the material with enhanced surface properties (figure 1, inset) compared to its previously known counterpart synthesized from the co-precipitation method provides higher rate capability with low capacity fade during long-term cycling.The XRD pattern of the material, with the Li2MnO3 region magnified, presented in Figure 1, perfectly matches with the literature data( 3 ) for the layered Li-rich MNC material of similar composition. We obtained discharge capacities of approximately 300, 250, 200 and 150 mAh/g at C/20, C/4, and C and 2C discharge rates for electrodes having an active material loading of approximately 7 mg/cm2. Remarkably, excellent capacities with practically zero capacity fade has been observed for hundreds of cycles at the C discharge rate as shown in Figure 2 for a Li half-cell cycling between 2-4.9V at room temperature. Detailed structural and electrochemical properties of the material characterized using cyclic voltammetry (CV), XRD, X-ray Absorption Spectrometry (XAS), FESEM and High Resolution Transmission Electron Microscopy (HRTEM) will be discussed.

Reaction Dynamics of Magnesium Ions Insertion/Extraction of Olivine-Type FePO4

Magnesium battery is one of the candidates for the next generation battery system due to the high energy density and the environmentally friendly nature 1,2. Developing suitable cathode materials is a clue to the practical application. Divalent Mg2+ insertion/extraction reactions in host compounds is difficult, due to the stronger ionic interaction and harder charge redistribution of magnesium compared to lithium ions 3. Therefore suitable cathode materials are limited at this moment. In order to design the host materials for magnesium battery cathodes, it is important to understand the difference between the reaction dynamics of magnesium and that of lithium. Olivine-type lithium iron phosphate (LiFePO4) is a well-known cathode material in lithium ion batteries 4. By using delithiated FePO4, the electrochemical insertion/extraction of magnesium ions in FePO4 was reported by Le Paul et al. 5 Hence, FePO4 is suitable as a model compound to clarify the reaction dynamics of magnesium battery. In this study, we investigated the crystal structure change and the reaction dynamics during electrochemical magnesium insertion/extraction reactions of olivine-type FePO4.LiFePO4 was prepared by using a solid state reaction using Li2CO3, FeC2O4-2H2O and (NH4)2HPO4 as raw materials. After carbon-coated with acetylene black 10 wt% to LiFePO4, the mixture was pelletized and calcined. FePO4 was prepared by chemical oxidation of the obtained carbon coated LiFePO4 using nitronium tetrafluoroborate (NO2BF4) as an oxidizing agent. The particle size of the completed carbon coated FePO4 was about 65 nm determined by SEM observation. Electrochemical measurements were carried out using a three-electrode cell with an Ag+/Ag double junction reference electrode. The cathode material consists of 80 wt% FePO4, 15 wt% acetylene black and 5 wt% polytetrafluoroethylene. The counter electrode was a magnesium rod and the electrolyte was 0.5 M magnesium trifuluoromethanesulfonyl-imide (Mg(TFSI)2) in acetonitrile (AN). Galvanostatic discharge/charge measurements were conducted with C/30 rate at 55°C. X-ray absorption spectroscopy (XAS) measurements were carried out in a transmission mode at BL02B2 at SPring-8, Japan. Synchrotron X-ray diffraction (XRD) measurements were also carried out at BL01B1 and BL14B2 at SPring-8, Japan. Figure 1 shows discharge/charge profile of FePO4 in 0.5 M Mg(TFSI)2/AN. The obtained discharge capacity indicates 0.4 magnesium ions insertion into FePO4, comparable to 0.8 lithium ions insertion. In the charge process, the obtained capacity corresponds to the extraction of 0.3 magnesium ions. This result shows that magnesium insertion /extraction reaction of FePO4is irreversible and that the extraction is more difficult than the insertion process. In addition, discharge/charge curves are considerably dissimilar, suggesting that the reaction mechanism could be quite different between insertion and extraction processes. In order to characterize discharged and charged MgxFePO4, XAS and XRD measurements were performed. Fe K-edge XANES spectra shows lower and higher energy shifts with the discharge/charge reactions, respectively. This indicates the reduction and oxidation of Fe in FePO4 by magnesium insertion/extraction. XRD patterns show lower and higher peak shifts with the discharge/charge reactions, respectively. The peaks attributed to the two-phase reaction did not appear as shown in the charge/discharge reactions of LiFePO4. This result reveals that magnesium ions insertion/extraction reactions of FePO4proceeds via not a two-phase but a single-phase mechanism. Furthermore, we will present the reaction dynamics of magnesium ions insertion/extraction by using FePO4thin film as a model electrode. Acknowledgments This work was supported in part by Core Research for Evolutional Science and Technology (CREST) program of Japan Science and Technology Agency (JST) in Japan.

Long Cycle-life Organic Electrode Material based on an Ionic Naphthoquinone Derivative for Rechargeable Batteries

The applicability of the redox reactions of 5,8-dihydroxy-1,4-naphthoquinone (1) and its lithium salt, 5,8-dihydroxy-1,4-naphthoquinone dilithium salt (2), as positive electrode active materials for rechargeable lithium batteries was investigated. The prepared electrodes showed initial discharge capacities of 170 mAh g(1)−1 with an average voltage of 2.2 V vs. Li+/Li, and 247 mAh g(2)−1 with an average voltage of 2.1 V vs. Li+/Li for 1 and 2, respectively. The obtained discharge capacities correspond to their two-electron redox behaviors. While the electrode using 1 suffered from a poor cycle-stability, the one using 2 underwent many cycles; i.e., after a small drop in the capacity at the first cycle, the capacity of the latter electrode hardly decayed during the subsequent 100 cycles. The effects of the introduction of ionic groups on the physical properties including the cycle stability were discussed along with quantum chemistry calculation results.

Supercritical hydrothermal synthesis of rod like Li2FeSiO4 particles for cathode application in lithium ion batteries

A cheap and rapid supercritical hydrothermal method has been adopted for the synthesis of Li2FeSiO4 cathode materials for the application in lithium ion battery. The as-synthesized Li2FeSiO4 particles at 380°C exhibited rod like morphology with 20–80nm in diameter and 500nm–1μm in length characterized by transmission electron microscopy (TEM). The Li2FeSiO4 material is systematically characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermo gravimetric analysis (TG), scanning transmission electron microscopy (STEM) and energy dispersive X-ray (EDX). The electrochemical measurements were carried out after coating of Li2FeSiO4 particles with different weight percentage of conductive carbon. The discharge capacity of as-synthesized rod like Li2FeSiO4 with 30wt% conductive carbon coating exhibited 177mAhg−1 for the first cycle, which is more than that of as-synthesized and 20wt% conductive carbon coated rod like Li2FeSiO4 particles. The obtained discharge capacity is the highest for this material without high temperature heat treatment, which indicating that rod like morphology with diameter 20–80nm could be more active during electrochemical reactions.

Dialkoxybenzoquinone-type Active Materials for Rechargeable Lithium Batteries: The Effect of the Alkoxy Group Length on the Cycle-stability

The performance of 2,5-di-n-decyloxy-1,4-benzoquinone (DDBQ) as an active material for rechargeable lithium batteries was investigated. The prepared electrode in which DDBQ was incorporated showed an initial discharge capacity of 125 mAh/g(DDBQ) with an average voltage of 2.5V vs. Li+/Li. The obtained discharge capacity corresponds to a benzoquinone-based two-electron redox behavior. In the cycle-life test, the prepared DDBQ- electrode showed a relatively good performance; it maintained about 60% of the initial capacity after 20 cycles. The observed cycle-stability was compared to those of the other dialkoxybenzoquinones bearing shorter alkoxy chains, such as the methoxy, ethoxy, and propoxy groups. The correlation between the cycle-stability and the solubility in the electrolyte solvent was discussed.

Crystalline polycyclic quinone derivatives as organic positive-electrode materials for use in rechargeable lithium batteries

Abstract The performance of 9,10-anthraquinone (AQ), and 5,7,12,14-pentacenetetrone (PT) as active materials for rechargeable lithium batteries was investigated. Positive-electrodes in which AQ and PT were incorporated showed initial discharge capacities of greater than 200 mAh/g (AQ or PT) . The obtained discharge capacities suggest that a multi-electron redox reaction takes place in each derivative. The discharge capacity of the positive-electrode with AQ rapidly decreased during the charge/discharge cycles; however, the positive-electrode with PT showed a relatively good cycle-life performance; it maintained about 80% of the initial capacity even after 100 cycles.

Cycle mechanism and electrochemical properties of lithium manganese oxide prepared using different Mn sources

Li 2MnO 3 powders were synthesized using the solid-state reaction with different Mn sources (Mn 3O 4 and γ-MnOOH). The Li 2MnO 3 powders were characterized by means of XRD, SEM, TEM, and electrochemical testing. The resulting Li 2MnO 3 powders showed different physical properties and electrochemical reversible capacities depending on their synthetic temperatures and Mn sources. The obtained discharge capacities of two Li 2MnO 3 materials decreased with increasing calcination temperature. The Li 2MnO 3 synthesized using Mn 3O 4 as the starting material showed a high discharge capacity over 160 mAh g −1 after 25th cycle. It was found that the resulting Li 2MnO 3 powder using Mn 3O 4 was a composite consisting of monoclinic Li 2MnO 3, LiMnO 2, and LiMn 2O 4 phases. The reversible discharge capacity of Li 2MnO 3 in this study originated from the transformation between layered LiMnO 2 and cubic LiMn 2O 4 phases, which was confirmed by the differential capacity, ex situ XRD, and HRTEM results.

LiNi[sub 0.5]Mn[sub 1.5]O[sub 4] Showing Reversible Phase Transition on 3 V Region

Spinel LiNi 0 . 5 Mn 1 . 5 O 4 powders with different space group of Fd3m and P4 3 32 were synthesized by an ultrasonic spray pyrolysis method. The morphologies of the prepared powders depended on their structures; polyhedral shape for Fd3m and octahedral for P4 3 32. The obtained discharge capacities of the Fd3m and P4 3 32 were about 60 mAh g - 1 and 70 mAh g - 1 , respectively. Structural changes of both compounds were investigated on 3 V region by ex situ X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). From the ex situ XRD and HRTEM studies, LiNi 0 . 5 Mn 1 . 5 O 4 having P4 3 32 symmetry showed that structural transition occurred reversibly from simple cubic (P4 3 32) to tetragonal phase (I4 1 /amd), whereas irreversible structural changes were observed for Fd3m symmetry on 3V region.

Synthesis and electrochemical performance of amorphous hydrated iron phosphate nanoparticles

Amorphous hydrated iron (III) phosphate nanoparticles with average particle size of 80 nm were synthesized by a facile coprecipitation method at ambient temperature. The obtained sample was characterized by X-ray powder diffraction (XRD), thermogravimetrical analysis (TGA), and scanning electron microscopy (SEM). The electrochemical performances of the samples as cathode active materials were investigated in the 3.8–2.0 V range at a current density of 0.4 mA cm −2. The results show that the obtained discharge capacity was improved for amorphous FePO 4·2H 2O.

The effects of sintering time on the structure and electrochemical properties of Li(Ni 0.8Co 0.2)O 2

We present the findings of a new study on the effects of sintering time on the structure and electrochemical properties of layered Li(Ni 0.8Co 0.2)O 2. For this study, we have examined samples prepared with sintering times of 3, 24, 48 and 96 h. The structure was initially examined by powder X-ray diffraction and then more precisely by time of flight powder neutron diffraction, with structural analysis by the Rietveld method being performed. The structural analysis indicated differences in the Li 3a and Ni/Co 3b site occupancies, which appear to be related to the sintering times. Electrochemical charge/discharge measurements indicated that the initial discharge capacities for the samples prepared at 3, 24, and 48 h were basically invariant. However, a sizeable increase was noted for the sample prepared with a sintering time of 96 h. Also, an increase in the obtained discharge capacity from the first to second cycles was found for the samples prepared with 3–48 h sintering times. The largest increase was noted for the sample prepared for 48 h. No increase was seen for the sample sintered for 96 h. However, for all samples examined in this work, the capacities on first discharge were in excess of 180 mA h/g.

Performance evaluation of LaNi 4.7Al 0.3 and LaNi 5 electrodes used as anodes in nickel/metal hydride secondary batteries by analysis of current transients

The performance of LaNi 4.7Al 0.3 and LaNi 5 porous electrodes used as anodes in nickel/metal hydride secondary batteries has been evaluated by analysis of current decay transients. From the measured three-staged current decay transients for the hydrogen transport through both electrodes in the coexistence of two hydride phases, the discharge capacity and β-to α-phase transition time were determined. The optimum charging condition and velocity of α/ β phase boundary movement are discussed with respect to the experimentally obtained discharge capacity and transition time. The potentiostatic current decay transient technique is more conveniently employed to establish the optimum charging condition, as compared with the usual galvanostatic charge-discharge technique.