Physical characteristics and rate performance of (CFx)n (0.33 < x < 0.66) in lithium batteries

Sub-fluorinated graphite fluorides (CF_x)_n compounds, 0.33 < x < 0.63 were prepared from natural graphite and characterized by TGA, SEM-EDX and XRD. Their cathode behavior in lithium batteries was investigated under different discharge rates and compared to commercial petroleum coke based (CF)_n. At low discharge rate, the energy density increases with the fluorine content x. However, at higher rates, sub-fluorinated compounds performed better than commercial (CF)_n. The result is discussed with relation to higher electrical conductivity of sub-fluorinated compounds.     

Carbon-coated fluorinated graphite for high energy and high power densities primary lithium batteries

The electrochemical performances of fluorinated graphite have been improved by coating a uniform carbon layer on commercial CF_x (x = 1) powder used as cathode material in lithium battery. In comparison with the cell using un-coated CF_x as cathode, the cell using carbon coated CF_x cathode has a higher energy density and higher power density, particularly at higher discharge current rates (1C above). This is because the conductive carbon coating provides the exterior connectivity between particles for facile electron conduction, resulting in high rate performance.     

Performance characteristics of Li/MnO2-CFx hybrid cathode jellyroll cells

The performance characteristics of a hybrid cathode system containing manganese dioxide and carbon monofluoride are described. This novel cathode mixture provides a synergistic effect offering the most beneficial performance properties of each material. Cylindrical jellyroll cells constructed with this cathode system possess: high energy density, high initial cell voltage (no voltage delay), high rate capability, moderate material cost, stable discharge reaction products, a safe, non-noxious electrolyte, and excellent shelf properties. Performance characteristics are compared with CF_x, MnO₂ and SO₂-lithium cells.     

The preparation of NaV1−xCrxPO4F cathode materials for sodium-ion battery

The key to development of sodium-ion battery is the preparation of cathode/anode materials. Cr doped NaV_1−xCr_xPO₄F (x = 0, 0.04, 0.08) were prepared by the high temperature solid-state reaction for the application of cathode material of sodium-ion batteries. The structures and morphologies of the cathode materials were characterized by Flourier-infrared spectra (FT-IR), X-ray diffraction (XRD) and scanning electron microscope (SEM). The effects of Cr doping on performances of the cathode materials were analyzed in terms of the crystal structure, charge–discharge curves and cycle performances. The results showed that the as-prepared Cr-doped materials have a better cycle stability than the un-doped one, an initial reversible capacity of 83.3 mAh g⁻¹ can be obtained, and the first charge–discharge efficiency is about 90.3%. In addition, it was also observed that the reversible capacity retention of the material is still 91.4% in the 20th cycles.     

Solid-State Nuclear Magnetic Resonance Studies of Electrochemically Discharged CF(x)

Electrochemical studies of three types of CF_x (F - fiber based, C - petroleum coke based, G - graphite based) have demonstrated different electrochemical performances in previous work, with fiber based CF_x delivering superior performance over those based on petroleum coke and graphite. ¹³C and ¹⁹F MAS (magic angle spinning) NMR techniques are employed to identify the atomic/molecular structural factors that might account for differences in electrochemical performance among the different types of CF_x. Small quantitative variations of covalent CF and LiF are noted as a function of discharge and sp³ bonded carbons are detected in discharged F type of CF_x.     

Vapor-grown carbon fiber anode for cylindrical lithium ion rechargeable batteries

A lithium ion rechargeable battery based on carbon anode that is a viable replacement for lithium metal anode has been developed. In this investigation, the Vapor-Grown Carbon Fiber was used as the anode material of a cylindrical battery. The charge/discharge experiments were carried under various temperatures and current densities. Excellent cyclability was obtained at 21°C at a charge/discharge of 0.8 C with three cathode materials (LiCoO₂, LiMn₂O₄, and LiNiO₂). High discharge capacity was obtained at low temperature (0°C). Good cyclability was also obtained at high temperature (40°C). At the charge/discharge rate of 4.0 C, energy density did not decay significantly. Good cyclability was obtained for rates ranging from 0.8 C to 4.0 C. Self-discharge was investigated at 3 temperatures (21, 40 and 60°C). The measured self-discharge was 8, 15 and 31% per month at 21, 40 and 60°C, respectively.     

Enhanced lithium-ion intercalation properties of coherent hydrous vanadium pentoxide-carbon cryogel nanocomposites

Coherent hydrous vanadium pentoxide (V₂O₅·nH₂O)-carbon cryogel (CC) nanocomposites were synthesized by electrodeposition of vanadium pentoxide onto the porous carbon scaffold which was derived from resorcinol (R) and formaldehyde (F) organic hydrogels. As-fabricated nanocomposites were characterized by scanning electron microscopy (SEM), along with EDAX and nitrogen sorption isotherms which suggested vanadium pentoxide incorporated in the pores of carbon cryogels. The nanocomposites showed much improved discharge capacity and better cyclic stability as compared to hydrous vanadium pentoxide films deposited on platinum foil. The discharge capacity of the nanocomposites reached 280 mAh g⁻¹ based on the mass of the vandium pentoxide at a current density of 100 mA g⁻¹ and it possessed good cycle stability at different discharge rates. The results demonstrated that electrochemical performances, such as specific discharge capacitance and reversibility of the composite electrode, could be greatly enhanced by the introduction of carbon cryogels (CCs) scaffold with three-dimensionally interconnected porous structure in which V₂O₅·nH₂O homogeneously dispersed.     

A novel sol–gel method to synthesize nanocrystalline LiVPO4F and its electrochemical Li intercalation performances

Lithium vanadium fluorophosphate, LiVPO₄F, a cathode material for lithium ion batteries, was synthesized by a sol–gel method followed by low temperature calcinations. V₂O₅·nH₂O hydro-gel, NH₄H₂PO₄, LiF and carbon were used as starting materials to prepare a precursor, and LiVPO₄F was finally obtained by sintering the precursor at 550 °C for 2 h. X-ray diffraction results show that the LiVPO₄F sample is triclinic structure. TEM image indicates that the LiVPO₄F particles are about 70 nm in diameter embedded in carbon network. The LiVPO₄F system showed the discharge capacity of about 130 mAh g⁻¹ in the range of 3.0–4.6 V at the first cycle, and the discharge capacity remained about 124 mAh g⁻¹ after 30 cycles. The sol–gel method is suitable for the preparation of LiVPO₄F cathode materials with good electrochemical Li intercalation performances.     

Hydrogen evolution reaction at Pd-modified carbon fibre and nickel-coated carbon fibre materials

The present paper reports on A.C. impedance study of hydrogen evolution reaction (HER), carried-out on Pd-modified carbon fibre (CF) and nickel-coated carbon fibre (NiCCF) materials. The HER was examined in 0.5 M H₂SO₄ solution for electrochemically deposited Pd on Hexcel 12K AS4C CF and Toho-Tenax 12K50 NiCCF tow materials. Kinetics of the hydrogen evolution reaction was studied at room temperature, over the cathodic overpotential range: −100 to −1200 mV vs. RHE. Corresponding values of charge-transfer resistance, exchange current–density for the HER and other electrochemical parameters for the examined catalyst materials were derived. Thus, Pd modification of CF and NiCCF materials (at ca. 1.5 wt.% Pd) dramatically increased the exchange current–density parameter by about 5300× and 445× for carbon fibre and nickel-coated carbon fibre tows, correspondingly.     

A novel battery-supercapacitor system with extraordinarily high performance

In this paper, a battery-supercapacitor system is developed and its electrochemical performance is investigated. The battery-supercapacitor system is composed of a separated LiFePO₄/activated carbon cathode and a separated Li₄Ti₅O₁₂/activated carbon anode onto both sides of a piece of aluminum foil. We demonstrated the superior electrochemical performance of this battery-supercapacitor system, such as its energy density of 4.9–48.5 Wh/kg, power density of 167.7–5243.2 W/kg, rate capability of 73.9% at a current density of 20 A and cycle life (91.5% after 1800 cycles) which outperforms that of a hybrid supercapacitor. This can be explained by the synergistic effect of a Faradaic and non-Faradaic system in a single cell. The results clearly show that the battery-supercapacitor system, including a LiFePO₄ cathode/Li₄Ti₅O₁₂ anode and an activated carbon anode/activated carbon cathode, has great potential for use in advanced energy storage devices.     

Constructing a novel and safer energy storing system using a graphite cathode and a MoO3 anode

A cell employing a graphite cathode and a molybdenum (VI) oxide (MoO₃) anode is investigated as a possible energy storage device. Graphite cathode allows raising the voltage well above the cathode materials of LIBs without causing safety issues. The bottom potential of this anode is 2.0 V vs. Li/Li⁺, which is well above the lithium plating potential. Pulse polarization experiment reveals that no lithium deposition occurs, which further enhances the safety of the graphite/MoO₃ full cell. Charge/discharge mechanism of this system results from intercalation and de-intercalation of the PF₆⁻ in the cathode (KS-6) and Li⁺ in the anode (MoO₃). This mechanism is supported by in situ X-ray diffraction data of the graphite/MoO₃ cell recorded at various states of charge.     

High voltage spinel cathode materials for high energy density and high rate capability Li ion rechargeable batteries

We have synthesized LiMn_1.5Ni_0.4Cr_0.1O₄ cathode material for high energy density Li ion rechargeable batteries using sol-gel method. The synthesized materials were characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy, cyclic voltammetry and charge-discharge characteristics. It was found that phase pure materials were obtained an annealing temperature of 875 °C for 15 h. The maximum discharge capacity at a constant charge-discharge current rate 1C, 0.5C, and 0.2C were found to be about 99 mAh g⁻¹, 110 mAh g⁻¹, and 131 mAh g⁻¹, respectively. The capacity retentions after 50 charge-discharge cycles were found to be about 99%, 97%, and 97.3% at discharge current rates of 0.2C, 0.5C, and 1C. The stable electrochemical behavior of the above cathode material even at high C rate, showed that it could be used for high energy density and high rate capability Li ion rechargeable batteries.     

The improved discharge performance of Li/CFx batteries by using multi-walled carbon nanotubes as conductive additive

The discharge performance of Li/CF_x (x = 1) battery is improved by using multi-walled carbon nanotubes (MWCNTs) as an alternative conductive additive. Compared with the battery using acetylene black as conductive additive at the same amount, the Li/CF_x battery using MWCNTs as conductive additive has higher specific capacity and energy density as well as smoother voltage plateau, especially at higher discharge rate. The specific capacity at discharge rate of 1 C is improved by nearly 26% when MWCNTs are employed as conductive additive. Meanwhile, it is also found that the discharge performance is able to be tuned by the amount of MWCNTs and the battery containing more MWCNTs is favorable to be discharged at higher rates. The specific capacity of Li/CF_x battery with 11.09 wt.% MWCNTs is approximately 712 mAh g⁻¹ at the discharge rate of 1 C. It is proposed that the formed three-dimensional networks of MWCNTs in cathode, which enlarges the contact area of interphase and facilitates electrons delivery, accelerates the rates of lithium ion diffusion into the fluorinated layers and electrons transport in cathode at the same time, which improves the discharge performance of Li/CF_x battery subsequently, especially at higher rates.     

Synergistic effect of sulfur on electrochemical performances of carbon‐coated vanadium pentoxide cathode materials with polyvinyl alcohol as carbon source for lithium‐ion batteries

Vanadium pentoxide (V₂O₅) is a common cathode material for lithium‐ion battery, but its low electronic and ionic conductivity seriously affect its electrochemical performances. In this paper, a type of carbon‐coated V₂O₅ and S composite cathode material with PVA as the carbon source is utilized to lithium‐ion batteries. X‐ray diffraction and Raman test results illustrate that sulfur can make the V₂O₅ lose part of oxygen atoms and become nonstoichiometric vanadium oxide (V₂O_5‐x). Electrochemical test results show that sulfur can provide a considerable proportion of the specific capacity of the whole cathode. This illustrates that the synergistic effect of sulfur can optimize the structure of vanadium pentoxide in order to increase more electron transfer channels, and at the same time, it also can provide additional specific capacity for the whole cathode. When the ratio of V₂O₅ and sulfur is 1:3, the discharge specific capacity can reach 923.02, 688.37, and 592.70 mAh g^?1 at 80, 160, and 320‐mA g^?1 current density, respectively, and after 100 times charge and discharge cycles at 320‐mA g^?1 current density, the capacity retention rate can achieve to more than 60%.     

High performance hybrid supercapacitors with LiNi1/3Mn1/3Co1/3O2/activated carbon cathode and activated carbon anode

Hybrid supercapacitors have been studied as a next generation energy storage device that combines the advantages of supercapacitors and batteries. One important challenge of hybrid supercapacitors is to improve energy density (8.9–42 Wh/kg) with maintaining excellent power density (800–7989 W/kg) and cyclability (98.9% after 9000 cycles). Herein, we demonstrate an approach to design hybrid supercapacitors based on LiNi_1/3Mn_1/3Co_1/3O₂ (NMC)/activated carbon (AC) cathode and AC anode (NMC/AC//AC). The NMC/AC//AC hybrid supercapacitors shows outstanding electrochemical performances due to the enhanced energy and power densities. These findings suggest that the NMC/AC cathode is an effective method for high performance hybrid supercapacitors.     

Performance evaluation of carbon/PrBaCo2O5+δ composite electrodes for Li–O2 batteries

Herein, a new type of perovskite oxide PrBaCo₂O_5+δ (PBCO) was synthesized and optimized by cooperating with carbon nanotubes (CNT) or carbon nanoparticles (BP2000), which was further applied into Li–O₂ battery cathode as a bi-functional cathode catalyst, achieving a high discharge capacity of 15.1 mA h, the number of which is over four times than that of single PBCO or CNT cathode, and seven times than single BP2000 cathode. Furthermore, a significantly enhanced stability was achieved as sustained more than 290 cycles at a fixed capacity, the number of which exceeds most carbon-based and even other perovskite catalytic Li–O₂ batteries. The charge transfer resistance (R_ct) of PBCO was reduced 46.6% after cooperating with carbon materials, which is almost half of single PBCO. All these results demonstrated that the big defect of PBCO can be remedied through the surface decorating with electronic conductors, such as, carbon nano-materials, and thus resulting in a substantially enhanced cathodic performance.     

Physicochemical properties of lithium iron phosphate‐carbon as lithium polymer battery cathodes

Lithium iron phosphate‐carbon (LiFePO₄/multiwalled carbon nanotubes (MWCNTs)) composite cathode materials were prepared by a hydrothermal method. In this study, we used MWCNTs as conductive additive. Poly (vinylidene fluoride‐co‐hexafluoropropylene)‐based solid polymer electrolyte (SPE) was applied. The structural and morphological performance of LiFePO₄/MWCNTs cathode materials was investigated by X‐ray diffraction and scanning electron microscopy/mapping. The electrochemical properties of Li/SPE/LiFePO₄‐MWCNTs coin‐type polymer batteries were analyzed by cyclic voltammetry, ac impedance and galvanostatic charge/discharge tests. Li/SPE/LiFePO₄‐MWCNTs polymer battery with 5 wt % MWCNTs demonstrates the highest discharge capacity and stable cyclability at room temperature. It is indicated that LiFePO₄‐MWCNTs can be used as the cathode materials for lithium polymer batteries. Copyright © 2011 John Wiley & Sons, Ltd.     

Development of coin-type lithium-ion rechargeable batteries

We developed coin-type lithium-ion rechargeable batteries made of crystalline V₂O₅ for the cathode and pitch-based carbon for the anode. We optimized the capacity balance of cathode and anode materials. The batteries have a high operating voltage of about 2.7 V and excellent charge/discharge cycle characteristics. We also designed the batteries whose cathode potential is over 3 V versus lithium when the batteries are overdischarged to 0 V. Therefore, the batteries have excellent recovery characteristics even after overdischarge. The batteries have high energy density (about 100 Wh/l) which is about two times that of the coin-type NiCd batteries. It can serve as a memory backup power source with a single battery.     

Iron phthalocyanine as a cathode catalyst for a direct borohydride fuel cell

A direct borohydride fuel cell (DBFC) is constructed using a cathode based on iron phthalocyanine (FePc) catalyst supported on active carbon (AC), and a AB₅-type hydrogen storage alloy (MmNi_3.55Co_0.75Mn_0.4Al_0.3) was used as the anode catalyst. The electrochemical properties are investigated by cyclic voltammetry (CV), linear sweep voltammetry (LSV), etc. methods. The electrochemical experiments show that FePc-catalyzed cathode not only exhibits considerable electrocatalytic activity for oxygen reduction in the BH₄⁻ solutions, but also the existence of BH₄⁻ ions has almost no negative influences on the discharge performances of the air-breathing cathode. At the optimum conditions of 6 M KOH + 0.8 M KBH₄ and room temperature, the maximal power density of 92 mW cm⁻² is obtained for this cell with a discharge current density of 175 mA cm⁻² at a cell voltage of 0.53 V. The new type alkaline fuel cell overcomes the problem of the conventional fuel cell in which both noble metal catalysts and expensive ion exchange membrane were used.     

Novel porous carbon felt cathode modified by cyclic voltammetric electrodeposited polypyrrole and anthraquinone 2-sulfonate for an efficient electro-Fenton process

A novelty two-step synthesized porous carbon felt (PCF) cathode modified by cyclic voltammetric (CV) electrodeposited polypyrrole (Ppy) and anthraquinone 2-sulfonate (AQS) (PCF/Ppy/AQS) for an efficient electro-Fenton process has been investigated. Brunauer Emmett Teller (BET) and scanning electron microscope (SEM) measurements verified the three-dimensional porous structure of the PCF, revealing that the specific surface area was approximately 2.5 times higher than that of the bare carbon felt (CF), which ensured more active sites available for oxygen reduction reaction (ORR). In addition, the electrodeposited Ppy decreases the charge transfer resistance (R_ct) of the PCF cathode. AQS, a type of anthraquinone that can serve as an oxygen reduction catalyzer, could accelerate the ORR process and subsequently improve the performance of the electro-Fenton system. Rotating disk electrode (RDE) analysis confirmed that the ORR catalyzed by AQS was a double-electron reduction process, which contributed to hydrogen peroxide (H₂O₂) generation. The removal efficiency of total organic carbon (TOC) from Rhodamine B (RhB) could reach 51% within 1 h in the electro-Fenton system equipped with the PCF/Ppy/AQS, resulting in an improvement of approximately 24% compared with the bare CF cathode without porous treatment. The cycle experiment showed a good stability of the PCF/Ppy/AQS cathode. Additionally, the possible mechanism of degradation process in the electro-Fenton equipped with the PCF/Ppy/AQS cathode was proposed based on the electron paramagnetic resonance (EPR) analysis and quenching experiment. The novel fabricated PCF/Ppy/AQS provides an alternative as a high-efficiency cathode, yielding energy savings in the electro-Fenton system.