Charge-discharge Cycling Tests Research Articles

Effect of Volume Expansion on SEI Covering Carbon-Coated Nano-Si/SiO Composite

We prepared nano-sized Si clusters dispersed uniformly in carbon-coated SiO (C-Si/SiO) and thoroughly investigated the morphology of the solid electrolyte interface (SEI) formed on the C-Si/SiO electrodes before and after a charge-discharge cycling test. The 30 cycles at 1000 mAh/g (deep) showed an excellent durability compared to those at 500 mAh/g (shallow). The different SEIs with the crack-contained and smooth electrode surfaces were formed after the deep and shallow cycles, respectively. Their SEI components which originated from hydrocarbons, Li alkyl carbonate, Li2CO3, LiF, and phosphorus oxide, were almost identical, even though the surface morphology was much different. When charge-discharge from 0.02 V to 0.7 V with large-volume change was applied, large cracks were formed on the SEI surface of the C-Si/SiO electrode after shallow cycles, which was similar to that after deep cycles. As a result, the cell properties for shallow cycles corresponded roughly to those for deep cycles. This suggests that the charge-discharge of a C-Si/SiO electrode is strongly related to the surface morphology, meaning that stable cycle properties can be achieved by controlling the morphology of the SEI.

Effects of reduction and polystyrene sulfate functionalization on the capacitive behaviour of thermally exfoliated graphene

Thermally exfoliated and reduced graphite oxide (TEG) was prepared at high temperature (1000 °C). The supercapacitor behavior of the resulting TEG would be affected by the specific surface area (SSA) and the surface interactions of the remaining oxygen functional groups with the electrolyte media. The oxygen functional groups on the surface of TEG were controlled by varying the duration of thermal treatment (5, 10, 20, 30 and 45 s). Polystyrene sodium sulfate (PSS) functionalized TEG (PSS-f-TEG) was prepared to aid the interaction with the polar groups of the electrolyte media and its electrochemical performance was measured. Fourier transform infrared and X-ray photoelectron spectroscopy were used for the qualitative and quantitative detection of residual oxygen functionalities in the pristine graphite oxide and resulting TEGs. It was found that the residual oxygen functionalities in the TEGs decreased with increasing thermal treatment time and the SSA increased initially. A maximum SSA of 400.7 m2 g−1 was obtained for 30 s thermally treated TEG. The highest specific capacitance value of 278.8 F g−1 was observed for PSS-f-TEG (with 10 s treatment). It was found that the wettability of the TEG was increased after surface modification with PSS as evident from the contact angle analysis. The oxygen functionalities of graphene directly enhanced the specific capacitance by contributing pseudocapacitance. The 1000 charge–discharge cycle test showed long-term electrochemical stability of the electrode materials with 97% retention in specific capacitance.

Accelerated Charge–Discharge Cycling Test and Cycle Life Prediction Model for Supercapacitors in Alternative Battery Applications

Supercapacitors (SCs), which are mainly used in high-power applications, can be potential energy storage sources for alternative battery applications once their outstanding cycle life performance at wide temperature ranges is considered. Because the cycle life of SCs is inherently long, aging acceleration and cycle life prediction are of primary importance for practical usage. In this paper, the feasibility of accelerated cycle life testing is investigated and a cycle life prediction model of SCs for alternative battery applications is established. Charge-discharge cycling tests were performed for SCs at various cycling conditions for 3.8 years. The resultant capacitance retention trends were linearly extrapolated with the square root of the number of cycles as the x-axis. Capacitance degradations were mainly influenced by temperature, thus implying that aging can be accelerated by elevating the temperature. Activation energy values of capacitance degradations were obtained from the Arrhenius equation to determine the acceleration factor. By combining the extrapolation and the acceleration factor, the cycle life prediction model was established. Experimental and predicted cycle life trends agreed well, indicating that the established cycle life prediction model is appropriate for SCs in alternative battery applications.

Fabrication and performances of all solid-state symmetric sodium battery based on NASICON-related compounds

The electrochemical performance of a novel all solid-state sodium-ion symmetrical battery with Na3Zr2Si2PO12 (NASICON) as a solid electrolyte and Na3V2(PO4)3 (NVP) as the active electrode material was examined. The all solid-state cell was fabricated by a combination of screen printing and hot pressing. The electrochemical characterization of the NVP active material in the metallic sodium half-cells at 80°C indicated that this NASICON-related phosphate undergoes reversible sodium extraction/insertion reactions at electrode potentials of 1.6 and 3.4V vs. Na. These insertion properties allowed the NVP to function successfully as the active material for both the positive and negative electrodes in a sodium-ion cell configuration. A charge–discharge cycling test of the fabricated symmetrical all solid-state cell was carried out at room temperature within the voltage range of 0.01 and 1.9V. It was found that the cell can work as a secondary battery and showed first discharge capacities of 68 and 32mAhg−1 at the current densities of 1.2 and 10μAcm−2, respectively. Furthermore, the lack of reactivity between the all-solid-state cell components during long-term cycling was confirmed.

Improvement of electrochemical properties of MgO-coated LiNi0.4Co0.2Mn0.4O2 cathode materials for lithium ion batteries

The surface of LiNi0.4Co0.2Mn0.4O2 cathode is coated using MgO coating materials. The electrochemical properties of the coated materials are investigated as a function of the pH value of the coating solution and the composition of coating materials. Their microscopic structural features have been investigated using scanning electron microscopy and X-ray diffraction. The electrochemical properties of the samples were monitored using coin-cell by galvanostatic charge–discharge cycling test, EDS test, EIS test, and cyclic voltammetry. The coating solution with pH = 10.5 is found to be favorable for the formation of stable coating layers, which enhances the electrochemical properties. In contrast, 2 % MgO-coated LiNi0.4Co0.2Mn0.4O2 shows better cycle performance and rate capability than the bare sample. Such enhancements are attributed to the presence of a stable MgO layer which acts as the interfacial stabilizer on the surface of LiNi0.4Co0.2Mn0.4O2.

Sol–gel preparation and electrochemical properties of La-doped Li4Ti5O12 anode material for lithium-ion battery

A sol–gel method using Ti(OC4H9)4, LiCH3COO·2H2O, and La(NO3)3·6H2O as starting materials and ethyl acetoacetate as chelating agent to prepare pure and lanthanum (La)-doped Li4Ti5O12 is reported. The structure and morphology of the active materials characterized by powder X-ray diffraction and scanning electron microscopy analysis indicate that doping with a certain amount of La3+ does not affect the structure of Li4Ti5O12, but can restrain the agglomeration of the particles during heat treatment. The electrochemical properties measured by cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge–discharge cycling tests show that La-doped Li4Ti5O12 presents a much improved electrochemical performance due to a decrease in charge transfer resistance. At current densities of 1 and 5 C, the La-doped Li4Ti5O12 exhibits excellent reversible capacities of 156.16 and 150.79 mAh g−1, respectively. The excellent rate capability and good cycling performance make La-doped Li4Ti5O12 a promising anode material for lithium-ion batteries in energy storage systems.

Propylene oxide-assisted fast sol–gel synthesis of mesoporous and nano-structured LiFePO4/C cathode materials

LiFePO4/C nanocomposites are synthesized by a propylene oxide-assisted fast sol–gel method using FeCl3, LiNO3, NH4H2PO4, and sucrose as the starting materials. It was found that after adding propylene oxide into the solution containing the starting materials, a monolithic jelly-like FePO4 gel containing lithium and carbon source is generated in a few minutes without controlling the pH value of the solution and a time-consuming heating process. Propylene oxide plays a key role in the fast generation of the precursor gel. The final products of LiFePO4/C are obtained by sintering the dry precursor gel. The structures, micro-morphologies, and electrochemical properties of the LiFePO4/C composites are investigated using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, nitrogen adsorption–desorption analysis, electrochemical impedance spectrum, and charge–discharge cycling tests. The results indicate that the LiFePO4/C composite prepared by sintering the precursor gel at 680 °C for 5 h is about 30 nm in size with a meso-porous structure (the main pore size distribution is around 3.4 nm). It delivers 166.7 and 105.8 mAh g−1 at 0.2 and 30 C, respectively. The discharge specific capacity is 97.8 mAh g−1 even at 40 C. The cycling performance of the prepared LiFePO4/C composite is stable. The excellent electrochemical performance of the LiFePO4/C composite is attributed to the nano-sized and mesoporous structure of LiFePO4/C and the in-situ surface coating of the carbon. It was also found that propylene oxide is crucial for the generation of mesoporous and nano-structured LiFePO4/C.

Water-Soluble Polyacrylic Acid as a Binder for Sulfur Cathode in Lithium-Sulfur Battery

Polyacrylic acid (PAA) as a binder in the aqueous solvent is applied in the preparation of sulfur cathode for lithium-sulfur battery. Electrochemical performances are investigated by a charge-discharge cycle test, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). CV and EIS tests indicate that the PAA sulfur cathode has smaller resistance and better kinetics characteristics than that of the poly(vinylidene fluoride) (PVDF) sulfur cathode using PVDF as a binder in N-methy-2-pyrrolidone (NMP) solvent. The charge-discharge tests show that the discharge capacity and the coulombic efficiency of the PAA sulfur cathode are 325 mAh g −1 and 89.5% at the 50th cycle at the current density of 335 mA g −1 . Compared with the PVDF sulfur cathode, the PAA sulfur cathode shows considerably a better cyclability. These results show that the PAA binder has great potential for lithium-sulfur battery applications.

Fabrication of graphene/polypyrrole nanotube/MnO2nanotube composite and its supercapacitor application

A novel composite is fabricated through hybridizing graphene with polypyrrole (PPY) nanotube and manganese dioxide (MnO 2 ) nanotube to comprehensively utilize the electrical double layer capacitance and pseudo-capacitance. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy are employed to characterize its structure. The SEM and TEM images illustrate that graphene/PPY nanotube/MnO 2 nanotube composite (GPM) presents interconnected structure. The result of Raman analysis demonstrates the intimate interactions among PPY, graphene and MnO 2 . In addition, cyclic voltammetry (CV), galvanostatic charge-discharge and electrochemical impedance spectroscopy (EIS) techniques are used to measure the electrochemical properties. It is revealed that GPM presents excellent high-rate performance and its capacitance is as high as 469.5 Fg −1 at a current density of 0.3 Ag −1 , higher than that of PPY and chemically reduced graphene sheet as well as the materials reported in the literature. Furthermore, long-term charge-discharge cycle test confirms that the fabrication of GPM can effectively merge the merits of graphene, PPY and MnO 2 . Additionally, EIS analysis illustrates that the presence of conductive graphene as well as the intimate interactions among graphene, PPY and MnO 2 lead to the good electrochemical stability.

The Preparation and Performance Study of Tin-Nickel Alloy Based Lithium Battery Anode Material

Based on copper foil, this paper takes electrodeposition to prepare tin-nickel alloy based anode material, which is of Sn 81.23% (Mass Fraction, the same as below), and Ni 18.77% (Mass Fraction, the same as below). It also studies the plating state, and plating structures and its electrochemical properties under heat treatment at different temperatures. The X-ray diffraction analysis (XRD) shows that the plating structures are all Ni3Sn4 and unalloyed individual-phase Sn under plating state and 200 oC heat treatment, and are Ni3Sn2 , Sn, Ni3Sn2 , Ni3Sn4 under 300 oC and 450 oC heat treatment respectively. In a button cell, which was made up with lithium slice, the results of charge-discharge cycle test and cyclic voltammetric curves test indicate that tin-nickel alloy’s specific capacity and charge-discharge cycle performance are related to the heat treatment temperature and structure of lithium battery anode material. The plating under plating state and 200oC heat treatment has high specific capacity, and its charge-discharge stability is well above that of the plating under other temperatures. Under 200 oC heat treatment, the plating could crystallize better and increase its content of Ni3Sn4. Its charge-discharge stability would be well above that of the original plating state. The scanning electron microscope (SEM) shows that before discharging, the plating of tin-nickel alloy was made up of small spherical particles, which are uniform and dense. The plating began to swell and crack after 50 times charge-discharge, which may lead to rapidly attenuate the plating’s specific charging capacity.

Mesoporous Tin Phosphate as Anode Material for Lithium-Ion Cells

Mesoporous SnP2O7was synthesized via a surfactant templating method where an anionic surfactant, sodium dodecyl sulfate was used. X-ray diffraction (XRD) analysis indicates presence of mesostructure when the precursors were calcined at 200, 300 and 400 °C. Cyclic voltammetry tests carried out within 0-2.0 V (vs. Li/Li+) indicated that irreversible reduction of tin phosphate to form lithium phosphate phases and metallic tin occurred around 1.10 V and 0.69 V whereas the reversible alloying and de-alloying reaction involving lithium with tin occurred at 0.19 V and 0.52 V, respectively. Galvanostatic charge-discharge cycling tests carried out within 0-1.2V (vs. Li/Li+) showed that the mesoporous tin phosphate calcined at 400 °C exhibited a reversible discharge capacity of 738 mAh/g in the second cycle and upon reaching the tenth cycle, it retained a discharge capacity of 461 mAh/g. The relatively high capacity obtained for this anode was attributed to the mesoporous framework which provided larger surface area for reaction with lithium and minimized effect of volume changes experienced by the anode during repeated charging and discharging cycling.

LiFePO<sub>4</sub>/Porous Carbon Nanocomposite Cathode Material for Lithium Ion Batteries

A LiFePO4/porous carbon nanocomposite was synthesized by using spontaneous precipitation combined with solid-state reaction. The microstructure, morphology and electrochemical properties of as-prepared samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), differential thermal analysis (TGA) and charge-discharge cycling tests. The results reveal that LiFePO4 particles are well-dispersed into porous carbon framework. The initial discharge of nanocomposite is 143 mAh g-1 at 0.1 C and 114 mAh g-1 at 1 C with satisfactory capacity retention. The superior electrochemical performance of the composites can be attributed to the nano-confined effect of conducting porous carbon and the nano-size of LiFePO4 particles in LiFePO4/porous carbon nanocomposite.

Electrochemical properties of a low molecular weight gel electrolyte for supercapacitor

A low molecular weight gel electrolyte was formed by the self-assembly of a low molecular weight gelator in KOH aqueous solution and first used as electrolyte in the supercapacitor. When the temperature was below 70°C, the gel electrolyte was solid-like. The electrochemical characteristics were investigated by impedance spectroscopy, cyclic voltammetry and charge–discharge cycle tests. As a result, the activated carbon supercapacitor with the low molecular weight gel electrolyte was found to exhibit higher specific capacitance (158.8mAhg−1) than that with the 6M KOH aqueous solution (156.6mAhg−1) after 150 cycles. Therefore, the low molecular weight gel electrolyte had good electrochemical properties while solving the problem of solution leakage. It was indicated that the low molecular weight gel electrolyte was a novel electrolyte for supercapacitors.

Li EXCESS Li4+xTi5-xO12-δ/C COMPOSITE USING SPRAY-DRYING METHOD AND ITS ELECTRODE PROPERTIES

We have prepared a lithium excess carbon composite material, Li 4+x Ti 5-x O 12-δ/ C (LTO/C), using various amounts of sucrose as a carbon source by the spray-drying method. The prepared materials were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and elemental analysis. The prepared material had the Li4Ti5O12 phase including 3.9–18.4 wt.% carbon. Transmission electron microscopy images and the selected area diffraction (SAD) pattern showed that the prepared materials consisted of a carbon nanonetwork in the LTO/C composite. The charge–discharge cycling tests were carried out using the R2032 coin-type cell under the following conditions; 1.2–3.0 V, 0.1 C–10 C (1 C = 175 mA g-1), 25°C. Based on the electrochemical results, the electrode performance of the prepared material was improved with increasing amounts of residual carbon, in particular, LTO/C including 6.2 wt.% residual carbon exhibited the best electrode performance of 156 mAh g-1 at 1 C during 50 cyclings when compared to the other materials.

Synthesis of γ-LiV2O5 nanorods as a high-performance cathode for Li ion battery

One-dimension γ-LiV2O5 nanorods were synthesized using VO2(B) nanorods as precursor in this study. The as-prepared material is characterized by X-ray diffraction, X-ray photoelectron spectrometry, Fourier-transform infrared, transmission electron microscopy (TEM), cyclic voltammetry, and charge–discharge cycling test. TEM results show that LiV2O5 nanorods are 90–250 nm in diameter. The nanorods deliver a maximum discharge capacity of 284.3 mAh g−1 at 15 mA g−1 and 270.2 mAh g−1 is maintained at the 15th cycle. Good rate performance is also observed with the discharge capacity of 250.1 and 202.6 mAh g−1 at 50 and 300 mA g−1, respectively. The capacity retention at 300 mA g−1 is 84.2% over 50 cycles. The Li+ diffusion coefficient of LiV2O5 is calculated to be 10-10–10−9 cm2 s−1. It is demonstrated that the nanorod morphology could greatly facilitate to shorten lithium ion diffusion pathways and increase the contact area between active material and electrolyte, resulting in high capacity and rate performance for LiV2O5.

A High‐Energy‐Density Redox Flow Battery based on Zinc/Polyhalide Chemistry

Zn and the Art of Battery Development: A zinc/polyhalide redox flow battery employs Br(-) /ClBr(2-) and Zn/Zn(2+) redox couples in its positive and negative half-cells, respectively. The performance of the battery is evaluated by charge-discharge cycling tests and reveals a high energy efficiency of 81%, based on a Coulombic efficiency of 96% and voltage efficiency of 84%. The new battery technology can provide high performance and energy density at an acceptable cost.

Effect of Mg-doping on the degradation of LiNiO2-based cathode materials by combined spectroscopic methods

The performance of a LiNiO2-based cell has been shown to be significantly improved by Mg-doping of LiNi0.8Co0.15Al0.05O2 (Mg-doped NCA) cathode materials. In the present study, the effects of Mg-doping were examined by electrochemical impedance spectroscopy (EIS) and scanning transmission electron microscopy-electron energy loss spectroscopy. EIS analysis revealed that the activation energy of Mg-doped NCA for the charge-transfer reaction was larger than that of undoped NCA by a factor of ∼10%; however, the charge-transfer resistance for Mg-doped NCA did not vary significantly with cycling, suggesting a different microstructure evolution compared to that of the undoped NCA. The spatial mapping of the product phases in the Mg-doped samples showed less degradation after charge–discharge cycling tests at 70°C compared to that in the undoped samples. In addition, degraded regions observed near the surface of the primary active material particles were identified as an intermediate structure, containing tetrahedrally coordinated Ni in contrast to the NiO-like phase found in the undoped samples. These microstructural observations are consistent with the electrochemical measurements.

Average and Local Structure Analyses of Li(Mn1/3Ni1/3Co1/3−xAlx)O2 Using Neutron and Synchrotron X-ray Sources

We prepared Li(Mn1/3Ni1/3Co1/3-xAlx)O2 by a solution method, and then investigated the electrode characteristics and average and local structures. From the charge-discharge cycle tests, it was found that Li(Mn1/3Ni1/3Co2/9Al1/9)O2 exhibited a worse cycle performance than Li(Mn1/3Ni1/3Co1/3)O2. In order to clarify the reason for this decrease from the viewpoint of the crystal structure, the average structures of the samples were studied by the Rietveld and Maximum Entropy Method (MEM) techniques using the neutron and synchrotron X-ray diffraction patterns. As a result, it was found that the Al substitution did not have a significant effect on the average structure. In order to reveal the local structures, we also performed X-ray absorption fine structure (XAFS) and Pair Distribution Function (PDF) analysis using neutron scattering data. These analyses implied that the stacking of the transition-metal layers varied by the partial substitution of Al for Co, and the arrangement had an influence on the cathode properties.

Quasi-solid-state electric double layer capacitors assembled with sulfonated poly(fluorenyl ether nitrile oxynaphthalate) membranes

A series of sulfonated poly(fluorenyl ether nitrile oxynaphthalate) (SPFENO) copolymers with different degrees of sulfonation were synthesized. Their degree of sulfonation was controlled by adjusting the molar ratio of the reactants. The polymer electrolytes prepared with a SPFENO membrane exhibited high ionic conductivities and solution holding capacity, which depended on the degree of sulfonation. The quasi-solid-state electric double layer capacitors (EDLCs) consisted of activated carbon electrodes and polymer electrolytes were assembled, and their electrochemical characteristics were studied by cyclic voltammetry and charge-discharge cycle tests. A SPFENO membrane with proper degree of sulfonation was effective for maintaining high ionic conductivity and keeping good electrode–electrolyte interfacial contact during cycling, which resulted in good cycling performance of the EDLC.

Dependence of property, cathode characteristics, thermodynamic stability, and average and local structures on heat-treatment condition for LiNi 0.5Mn 0.5O 2 as a cathode active material for Li-ion battery

LiNi 0.5Mn 0.5O 2 was heat-treated under high oxygen-pressure and Ar-reducing conditions, and then the cathode properties, thermodynamic stability and average and local structures were investigated. From X-ray diffraction and ICP measurements, it was found that the pristine LiNi 0.5Mn 0.5O 2 had a single phase of the layered rock-salt structure although the Ni content was slightly rich compared with the nominal one. These characteristics were kept even after the heat-treatments. Charge–discharge cycle tests clarified that the cycle performance of LiNi 0.5Mn 0.5O 2 was improved by both the reducing and oxidizing treatments. From neutron diffraction and X-ray absorption fine structure measurements, the local distortion around the transition metal, especially Ni, was supposed to be one of the important factors to determine the cathode properties. It was also found that the sample with higher thermodynamic stability exhibited better capacity retention in the discharge–charge cycle tests.