Excellent Charge-discharge Cycling Stability Research Articles

Performance Enhancement of 4.8 V Li1.2Mn0.525Ni0.175Co0.1O2 Battery Cathode Using Fluorinated Linear Carbonate as a High-Voltage Additive

High-capacity Li-rich layered composite oxide, xLi2MnO3·(1-x)LiMO2 (M = Mn, Ni, Co), is a promising candidate cathode material for high-energy electrochemical energy storage. Enabling the high-performance of high-voltage cathode relies on an electrolyte breakthrough and the solid electrolyte interface (SEI) stabilization. In this study, the 0.6Li2MnO3·0.4LiNi0.45Co0.25Mn0.3O2 (Li1.2Mn0.525Ni0.175Co0.1O2, LMNC) cathode is operated at 2.5–4.8 V with 5 wt% fluorinated linear carbonate, di-(2,2,2 trifluoroethyl)carbonate (DFDEC), as a high-voltage electrolyte additive, for the first time and applied to a high-energy lithium-ion battery. The cathode with DFDEC outperforms that in electrolyte only, delivering a high capacity of 250 mAhg−1 with an excellent charge-discharge cycling stability at the rate of 0.2C. Upon the use of DFDEC, the cathode surface is effectively passivated by a stable SEI composed of DFDEC decomposition products, which inhibit a detrimental metal dissolution and structural cathode degradation. A full-cell based on the SEI-stabilized LMNC cathode and graphite anode successfully demonstrates doubled energy density (∼278 Whkg−1) compared to ∼136 Whkg−1 of a commercialized cell of graphite//LiCoO2 and an excellent cycling stability.

Enhanced electrochemical performance of graphene modified LiFePO4 cathode material for lithium ion batteries

Abstract We report the synthesis of LiFePO 4 /graphene nano-composites using sol–gel method in the presence of dispersed graphene oxide mixed with LiFePO 4 precursors. The phase purity of the nano-LiFePO 4 /graphene composite was confirmed by X-ray diffraction. The electronic conductivity of LiFePO 4 /graphene composite was found to be six orders of magnitude higher than that of pure LiFePO 4 synthesized following otherwise the same procedure without the addition of graphene. Scanning electron microscopy and transmission electron microscope images show LiFePO 4 particles being covered uniformly by graphene sheets throughout the material forming a three-dimensional conducting network. At low currents and charging rate of C/3, the capacity of the composite cathode reaches 160 mAh/g, which is very close to the theoretical limit. More significantly, the LiFePO 4 –graphene composite shows a dramatically improved rate capability up to 27 C and excellent charge–discharge cycle stability over 500 stable cycles in comparison with the LiFePO 4 without graphene.

CO2–expanded ethanol chemical synthesis of a Fe3O4@graphene composite and its good electrochemical properties as anode material for Li-ion batteries

In this work, we have developed a new method to synthesize a Fe3O4@graphene (Fe3O4@GN) composite. First, the precursor was synthesized through the decomposition of ferric nitrate in the presence of graphene oxide in the mixed solvent of CO2–expanded ethanol. Then, the precursor was converted to the Fe3O4@GN composite via thermal treatment in N2 atmosphere. With the help of the CO2–expanded ethanol, Fe3O4 nanoparticles were coated on the surface of GN completely and uniformly with high loading. However, it is difficult to load Fe3O4 particles onto the surface of GN and most of the Fe3O4 particles were deviated away from GN and aggregated to form larger units in pure ethanol. When used as anode for Li-ion batteries (LIBs), the Fe3O4@GN composite with a graphene content of 25 wt% synthesized in CO2–expanded ethanol manifested excellent charge–discharge cycling stability and rate performance compared with the sample synthesized in ethanol. Such improved electrochemical performances should be attributed to the intimate contact between the GN and Fe3O4 nanoparticles in the composite. Since the present method does not need tedious pre-treatment, surfactant, or precipitate, it is a green or sustainable technology and the solvents could be recycled easily after simple phase separation. This facile method can be extended to the synthesis of other metal oxide composites, which are expected to have good performance as anode materials for LIBs and other applications.

Facile synthesis of metal oxide/reduced graphene oxide hybrids with high lithium storage capacity and stable cyclability

We report an environment-friendly approach to synthesize transition metal oxide nanoparticles (NPs)/reduced graphene oxide (rGO) sheets hybrids by combining the reduction of graphene oxide (GO) with the growth of metal oxide NPs in one step. Either Fe2O3 or CoO NPs were grown onto rGO sheets in ethanol solution through a solvothermal process, during which GOs were reduced to rGO without the addition of any strong reducing agent, e.g. hydrazine, or requiring any post-high-temperature annealing process. The GO or rGO during the precipitation of metal oxide NPs may act as heterogeneous nucleation seeds to facilitate the formation of small crystal grains. This may allow more efficient diffusion of Li ions and lead to high specific capacities. These metal oxide NPs-rGO hybrids were used as anodes for Li-ion batteries, which showed high capacities and excellent charge-discharge cycling stability in the voltage window between 0.01 and 3.0 V. For example, Fe2O3 NPs/rGO hybrids showed specific capacity of 881 mA h g(-1) in the 90th cycle at a discharge current density of 302 mA g(-1) (0.3 C), while CoO NPs/rGO hybrids showed a lower capacity of 600 mA h g(-1) in the 90th cycle at a discharge current density of 215 mA g(-1) (0.3 C). These nanohybrids also show excellent capacities at high C rate currents, e.g. 611 mA h g(-1) for Fe2O3/rGO sample in the 300th cycle at 2014 mA g(-1) (2 C). Such synthesis technique can be a promising route to produce advanced electrode materials for Li-ion batteries.

Virus-Enabled Silicon Anode for Lithium-Ion Batteries

A novel three-dimensional Tobacco mosaic virus assembled silicon anode is reported. This electrode combines genetically modified virus templates for the production of high aspect ratio nanofeatured surfaces with electroless deposition to produce an integrated nickel current collector followed by physical vapor deposition of a silicon layer to form a high capacity silicon anode. This composite silicon anode produced high capacities (3300 mAh/g), excellent charge-discharge cycling stability (0.20% loss per cycle at 1C), and consistent rate capabilities (46.4% at 4C) between 0 and 1.5 V. The biological templated nanocomposite electrode architecture displays a nearly 10-fold increase in capacity over currently available graphite anodes with remarkable cycling stability.

Electropolymerization of ionic liquid substituted polyphenylene as supercapacitors materials

A new type of polyphenylene, ionic liquid (IL) 1,3-methylimidazolium hexafluorophosphate substituted, has been prepared by electrodeposition on Au electrode surface via pulse galvanostatic method in 1-butyl-3-methylimidazolium hexafluorophosphate solution. The obtained polymer film had a spherulitic morphology with smallest grains of around 500 nm. Infrared spectrometry revealed that polyphenylene was deposited to a certain extent. The capacitive behavior of the IL substituted polyphenylene was investigated by cyclic voltammetry (CV) and galvanostatic charge–discharge method in 0.2 mol L −1 H 2SO 4 aqueous solutions or pure IL [bmim]PF 6. The specific capacitance of the polymer at the charge–discharge current density of 1 mA cm −2 equaled 206 F g −1 in acidic aqueous solution or 164 F g −1 in [bmim]PF 6. Additionally, excellent charge–discharge cycle stability (over 85% value of specific capacitance remained after 600 charge–discharge cycles) and power characteristics of the polymer electrode were observed in both electrolytes.

Nickel–cobalt oxides/carbon nanoflakes as anode materials for lithium-ion batteries

Novel nickel–cobalt oxides/carbon nanoflakes with Ni/Co molar ratio = 1:1 and 1:2 have been synthesized by a convenient hydrothermal method followed by a simple calcination process. X-ray diffraction results showed that the composites were composed of NiO, Co 3O 4, and carbon. Scanning electron microscope measurements demonstrated that the composites were flakes less than 100 nm in thickness, and the corresponding energy dispersive spectroscopy mapping showed that the carbon was distributed homogeneously in the composites. The electrochemical results showed that the composite electrodes exhibited low initial coulombic efficiency and excellent charge–discharge cycling stability. Additionally, the effect of different Ni/Co molar ratios on the electrochemical properties of the composites was investigated, and better performance was obtained for the sample with a Ni/Co molar ratio of 1:2.

Preparation and capacitive properties of cobalt–nickel oxides/carbon nanotube composites

In this paper, nickel–cobalt oxides/carbon nanotube (CNT) composites were prepared by adding and thermally decomposing nickel and cobalt nitrates directly onto the surface of carbon nanotube/graphite electrode to form nickel and cobalt oxides. Carbon nanotubes used in this paper were grown directly on graphite substrate by chemical vapor deposition technique. The capacitive behavior of nickel–cobalt oxides/CNT electrode was investigated by cyclic voltammetry and galvanostatic charge–discharge method in 1 M KOH aqueous solutions. The results show that nickel–cobalt oxides/CNT composite electrode has excellent charge–discharge cycle stability (0.2% and 3.6% losses of the specific capacitance are found at the 1000th and 2000th charge–discharge cycles, respectively) and good charge–discharge properties at high currrent density. Additionally, the effect of Ni/Co molar ratio on specific capacitance of the composite electrode was investigated and the highest specific capacitance (569 F g −1 at 10 mA cm −2) is obtained at Ni/Co molar ratio = 1:1.

Preparation and characterization of manganese oxide/CNT composites as supercapacitive materials

Manganese oxide was synthesized and dispersed on carbon nanotube (CNT) matrix by thermally decomposing manganese nitrates. CNTs used in this paper were grown directly on graphite disk by chemical vapor deposition technique. The capacitive behavior of manganese oxide/CNT composites was investigated by cyclic voltammetry and galvanostatic charge–discharge method in 1 M Na 2SO 4 aqueous solutions. When the loading mass of MnO 2 is 36.9 μg cm − 2 , the specific capacitance of manganese oxide/CNT composite (based on MnO 2) at the charge–discharge current density of 1 mA cm − 2 equals 568 F g − 1 . Additionally, excellent charge–discharge cycle stability (ca. 88% value of specific capacitance remained after 2500 charge–discharge cycles) and power characteristics of the manganese oxide/CNT composite electrode can be observed. The effect of loading mass of MnO 2 on specific capacitance of the electrode has also been investigated.