CN103746100A - A kind of V2O5 nanoparticle/graphene lithium ion battery cathode material and preparation method thereof - Google Patents

Abstract

The invention relates to a V ₂ O ₅ nano particle/graphene (V ₂ O ₅ -GE) lithium ion battery cathode material and a preparation method thereof, belonging to the field of lithium ion battery cathode materials. The V ₂ O ₅ -GE positive electrode material described in the present invention is synthesized by a simple hydrothermal reaction, and is formed by distributing V ₂ O ₅ nanoparticles with a size of 20-40 nm on the surface of a two-dimensional transparent graphene sheet. Composite cathode material. Compared with V ₂ O ₅ nanoparticles, due to the introduction of graphene, V ₂ O ₅ -GE nanocomposites exhibit better electrochemical performance, with higher reversible specific capacity, better cycle stability and more excellent rate performance. Graphene nanosheets not only play the role of conductive network structure to improve the conductivity of the composite electrode, but also the flexible network structure maintains the stability of the electrode material structure, inhibits particle agglomeration and volume expansion, thereby improving V The electrochemical performance of ₂ O ₅ nanoparticles is expected to be applied to high-performance lithium-ion battery cathode materials.

Description

A kind of V 2o 5nano particle/graphene lithium ion battery positive electrode and preparation method thereof

Technical field

The present invention relates to a kind of anode material for lithium-ion batteries and preparation method thereof, specifically V ₂o ₅nano particle/Graphene (V ₂o ₅-GE) anode material for lithium-ion batteries and preparation method thereof.

Background technology

Lithium ion battery, as a kind of green, the reversible energy, can be widely used in portable electric appts and means of transportation.Most research mainly concentrates on specific energy and the useful life of improving battery.Because the storage lithium performance of lithium ion battery depends on positive electrode to a great extent, therefore, much research is devoted to develop the chemical property that new positive electrode improves lithium ion battery.In numerous positive electrodes, V ₂o ₅because it is cheap, reserves are abundant, easily synthetic, and energy efficiency and specific capacity relatively high, caused people's concern.V ₂o ₅be a kind of typical intercalation compound, there is layered crystal structure, be very beneficial for Li ⁺reversible insertion and de-embedding, in 2.0-4.0V voltage range, discharge and recharge, theoretical capacity can be up to 294mAh/g, more than general positive electrode as LiCoO ₂(140mAh/g), LiMn ₂o ₄(148mAh/g) and LiFePO ₄(170mAh/g) much higher.

Yet, V ₂o ₅intrinsic lithium ion diffusion coefficient (is about 10-12cm ²/ s ^-1) and conductance lower, these have hindered V ₂o ₅application.Existing many bibliographical informations the V of nanostructure ₂o ₅can be used as a kind of effective ways and improve to a certain extent these deficiencies, this is because nanostructure can shorten Li ⁺migration path, increases contacting between electrode and electrolyte.But the V of nanostructure ₂o ₅chemical property (comprising cycle performance and high rate performance) be still limited to conductivity, the dissolving of alum salt and the reunion of particle.Therefore, be badly in need of further improving nanometer V ₂o ₅performance.Being combined with material with carbon element, is that a kind of effective approach improves nanometer V ₂o ₅chemical property.

At present, Graphene is as a kind of new carbon, because its excellent properties is subject to people's extensive concern and becomes study hotspot.The carbon atom of Graphene is with sp ²hydridization connects, and forms bi-dimensional cellular shape crystal structure, makes it have great specific area, and shows very excellent electricity, calorifics and mechanical property.By V ₂o ₅the compound nano composite material of making of nano particle and Graphene, not only can effectively stop the reunion of nano particle, shortens the migration distance of lithium ion, improves the de-embedding efficiency of lithium ion; Meanwhile, due to the two-dimentional flexibility of Graphene, to nano particle is coated, can alleviate the change in volume causing in the de-embedding process of lithium ion, improve the cyclical stability of battery; And due to the good electric conductivity of Graphene, as backing material, played enrichment and transmitted electronic action, be conducive to reduce internal resistance.

Summary of the invention

One of object of the present invention is to provide a kind of V ₂o ₅nano particle/Graphene (V ₂o ₅-GE) anode material for lithium-ion batteries.

Two of object of the present invention is to provide the preparation method of this positive electrode.

Above-mentioned purpose of the present invention is achieved by following technical solution:

A kind of V ₂o ₅nano particle/graphene lithium ion battery positive electrode, is characterized in that, is of a size of the V of 20-40nm ₂o ₅nano particle is distributed in the transparent Graphene sheet body structure surface of two dimension.

A kind ofly prepare above-mentioned V ₂o ₅the method of-GE anode material for lithium-ion batteries, is characterized in that the concrete steps of the method are:

Utilize improvement Hummer method to take native graphite as the synthetic graphite oxide of raw material; Graphite oxide powder is scattered in to DMF (DMF), and ultrasonic processing 30min, forms stable graphene oxide (GO) dispersion liquid (1mg/mL);

Weigh a certain amount of vanadium acetylacetonate (IV) (C ₅h ₈o ₂v) join the GO dispersion liquid in above-mentioned steps, stir 1h, form the solution of stable homogeneous;

Again above-mentioned solution is transferred in water heating kettle, reacted 20 hours at 200 ℃; Be cooled to after room temperature centrifugal collection black precipitate; The precipitation obtaining is used to alcohol and washed with de-ionized water several times, and 80 ℃ are dried 6 hours;

Then by dried 400 ℃ of calcinings 2 hours that are deposited in, wherein heating rate is 10 ℃/min, finally obtains V ₂o ₅-GE anode material for lithium-ion batteries.

Adopt easy hydro-thermal reaction to successfully synthesize V ₂o ₅-GE nano composite anode material, described positive electrode is by the V that is of a size of 20-40nm ₂o ₅nano particle is distributed in the transparent Graphene sheet body structure surface of two dimension and forms.Than V ₂o ₅nano particle, due to the introducing of Graphene, V ₂o ₅-GE nano composite material shows more excellent chemical property, has higher reversible specific capacity, better cyclical stability and more excellent high rate performance.Graphene nanometer sheet has not only played the netted structure function of conduction, has improved the electric conductivity of composite electrode, and network structure has kept the stability of electrode material structure flexibly, has suppressed the expansion of particle agglomeration and volume, thereby has improved V ₂o ₅the chemical property of nano particle, is expected to be applied to high performance lithium ion battery anode material.

Accompanying drawing explanation

Fig. 1 V ₂o ₅nano particle (A) and V ₂o ₅the TEM figure (transmission electron microscope picture) of-GE nano composite material (B).

Fig. 2 V ₂o ₅nano particle and V ₂o ₅the XRD collection of illustrative plates (X ray diffracting spectrum) of-GE nano composite material.

Fig. 3 V ₂o ₅the TG curve chart of-GE nano composite material (thermogravimetric analysis curve chart).

Fig. 4 V ₂o ₅nano particle and V ₂o ₅-GE nano composite material is at the 2.0-4.0V voltage range cyclic voltammetry curve in front 2 cycles, and wherein sweep speed is 0.1mV/s.

Fig. 5 (A) V ₂o ₅nano particle and V ₂o ₅-GE nano composite material is at the charging and discharging curve of front 2 circulations of 2.0-4.0V voltage range, (B) V ₂o ₅nano particle and V ₂o ₅-GE nano composite material is at 2.0-4.0V voltage range cycle performance curve, and current density is 100mA/g.

Fig. 6 V ₂o ₅nano particle and V ₂o ₅cycle performance under the different current densities of-GE nano composite material.

Fig. 7 V ₂o ₅nano particle and V ₂o ₅the electrochemical impedance collection of illustrative plates of-GE nano composite material.

Embodiment

The invention provides a kind of V ₂o ₅nano particle/Graphene (V ₂o ₅-GE) preparation method of composite positive pole, should be appreciated that specific embodiment described herein, only in order to explain the present invention, is not intended to limit the present invention.

Embodiment 1:

According to document (J.Am.Chem.Soc., 2008,130,5856-5857) utilize improvement Hummer method to take native graphite as the synthetic graphite oxide of raw material.

40mg graphite oxide powder is scattered in DMF (DMF), and ultrasonic processing 30 minutes, forms stable graphene oxide (GO) dispersion liquid (1mg/mL).Weigh 1g vanadium acetylacetonate (IV) (C ₅h ₈o ₂v) be distributed in above-mentioned GO dispersion liquid, stir 1 hour.Form uniform and stable solution.Transferred in the water heating kettle of 50ml, 200 ℃ of reactions 20 hours.Solution is cooled to after room temperature, and the black precipitate that centrifugal collection obtains is used alcohol and washed with de-ionized water several times, and 80 ℃ are dried 6 hours.Dried 400 ℃ of calcinings 2 hours that are deposited in, wherein heating rate is 10 ℃/min, finally obtains V ₂o ₅-GE anode material for lithium-ion batteries.

The concrete steps of button cell assembling are as follows:

Electrode slice be take aluminium foil as collector, with the V preparing ₂o ₅nano particle or V ₂o ₅-GE nano composite material is active material, and acetylene black is conductive agent, and Kynoar (PVDF) is made adhesive, and three in mass ratio 80: 10: 10 mixed grindings is even, adds appropriate 1-METHYLPYRROLIDONE, stirs and forms even anode sizing agent; This anode sizing agent is coated on aluminium foil equably, after naturally drying, at vacuum drying oven 80 degree, dries, punching makes positive plate.

Electrode slice and the negative pole metal lithium sheet of preparation are assembled into 2025 type button simulated batteries, the LiPF that electrolyte is 1M ₆/ EC: DEC (1: 1, V/V) solution, being assemblied in the glove box that is filled with high-purity argon of battery completes; Adopt LAND battery test system at 2.0-4.0V voltage range, battery performance to be tested.

Fig. 1 is according to the obtained V of embodiment 1 ₂o ₅nano particle and V ₂o ₅the TEM figure of-GE nano composite material.As shown in the figure, V ₂o ₅nano particle (Figure 1A) is irregularly shaped, and particle mean size is 20-40nm, has the tendency of obvious reunion; And to V ₂o ₅-GE nano composite material (Figure 1B), can clearly observe V ₂o ₅nano particle is dispersed on two-dimentional graphene film, pattern and size and pure V ₂o ₅nano particle is similar.

Fig. 2 is according to the obtained V of embodiment 1 ₂o ₅nano particle and V ₂o ₅the XRD collection of illustrative plates of-GE composite material.As seen from the figure, V ₂o ₅nano particle is orthorhombic system structure (JCPDS#41-1426), and corresponding cell parameter is

there is no other assorted peaks, show V ₂o ₅nano particle has higher degree.Simultaneously, according to Scherrer formula, by (110) peak, infer that crystallite dimension is about 26nm, this and TEM result are substantially identical.It should be noted that V ₂o ₅the XRD diffraction maximum of-GE nano composite material and pure V ₂o ₅nano particle is similar, does not observe the characteristic peak of carbon, and this may be because Graphene content is relatively low.

In order to determine the V making according to embodiment 1 ₂o ₅the content of GE in-GE nano composite material, we have tested thermogravimetric (TG) curve (Fig. 3) of sample under air atmosphere.As shown in the figure, 350 ℃ of following V ₂o ₅the mass loss of-GE is 1.14%, and this may, because moisture evaporation causes, comprise moisture and the chemical bonded refractory Heshui of physical absorption; The thermal decomposition process of Graphene occurs in 400-600 degree, causes V ₂o ₅-GE quality has reduced 3.62%.Therefore, remove moisture loss, last Graphene content in composite material is about 3.89%.

The V of Fig. 4 for making according to embodiment 1 ₂o ₅nano particle and V ₂o ₅-GE nano composite material electrode is at the cyclic voltammetry curve of 2.0-4.0V voltage range.For V ₂o ₅-GE composite electrode, during reduction process, three characteristic peaks appear at 3.31,3.12 and 2.17V successively, show the lithiumation process of its multistep, respectively corresponding α-V ₂o ₅to ε-Li _0.5v ₂o ₅(3.31V), δ-LiV ₂o ₅(3.12V), γ-Li ₂v ₂o ₅(2.17V) transformation of phase:

$V_2{\mathrm{<figure-callout\; id="5"\; label="O"\; filenames="HSA0000100600790000041.png"\; state="\{\{state\}\}">O</figure-callout>}}_5+0.5{\mathrm{Li}}^{+}+{0.5e}^{-}\&LeftRightArrow;{\mathrm{Li}}_{0.5}{V}_2{O}_5---\left(1\right)$

${\mathrm{Li}}_{0.5}{V}_2{\mathrm{<figure-callout\; id="5"\; label="O"\; filenames="HSA0000100600790000041.png"\; state="\{\{state\}\}">O</figure-callout>}}_5+0.5{\mathrm{Li}}^{+}+{0.5e}^{-}\&LeftRightArrow;\mathrm{Li}{V}_2{O}_5---\left(2\right)$

$\mathrm{Li}{V}_2{O}_5+{\mathrm{Li}}^{+}+e^{-}\&LeftRightArrow;{\mathrm{Li}}_2{V}_2{O}_5---\left(3\right)$

In oxidizing process, three characteristic peaks appear at respectively 2.61V, 3.34V, and 3.5V, first peak and latter two peak be corresponding second step and the lithium ion deviate from first respectively.And V ₂o ₅electrode also demonstrates 3 pairs of redox peaks, but and V ₂o ₅-GE nano composite material is compared, and oxidation peak is offset to forward potential, and reduction peak is to negative sense potential shift.Obviously, under identical conditions, V ₂o ₅the oxidation-reduction potential of-GE is poor is less than pure V ₂o ₅electrode.This shows, V ₂o ₅electron mobility between nano particle and graphene film be improved significantly.

The V of Fig. 5 for making according to embodiment 1 ₂o ₅nano particle and V ₂o ₅the charging and discharging curve of-GE nano composite material and cycle performance figure.Fig. 5 A is V ₂o ₅and V ₂o ₅-GE electrode is at 2.0-4.0V voltage range, the charging and discharging curve of front 2 circulations when current density is 100mA/g.As seen from the figure, V ₂o ₅nano particle and V ₂o ₅-GE nano composite material all has three typical voltage platforms, consistent with above-mentioned CV curve test result, respectively a series of V in corresponding de-lithium embedding lithium process ₂o ₅crystal transition process.Pure V ₂o ₅nanoparticle electrode first discharge specific capacity is 261mAh/g, and coulomb efficiency is 95%, and second cycle down be to 211mA/g (be about first discharge specific capacity 80.8%), and corresponding coulomb efficiency is 99.6%.And V ₂o ₅-GE nano composite material electrode initial discharge specific capacity is 255mAh/g, and coulomb efficiency is 96.5%; With pure V ₂o ₅electrode is compared, V ₂o ₅-GE composite electrode shows better capability retention, and second recycle ratio capacity is 224mAh/g, and (be about initial discharge specific capacity 87.8%), coulomb efficiency is 99.8%.V ₂o ₅the capability retention of-GE nano composite material electrode and initial coulomb efficiency are all higher than pure V ₂o ₅electrode, shows the raising of its cycle performance.

Fig. 5 B is pure V ₂o ₅and V ₂o ₅-GE electrode is at 2.0-4.0V voltage range, front 100 cyclic curve figure when current density is 100mA/g.For pure V ₂o ₅electrode, after 100 circulations, specific discharge capacity is 129mAh/g, 49.4% of corresponding initial capacity, average each Capacity fading rate is about 0.506%.Yet, V ₂o ₅after 100 circulations of-GE composite electrode, specific discharge capacity is 153mAh/g, is 60.3% of first discharge specific capacity, and average each Capacity fading rate is about 0.397%.Show that being introduced in of Graphene improved V to a certain extent ₂o ₅the cyclical stability of nano particle.It should be noted that V ₂o ₅-GE composite electrode is mainly decayed and is occurred in front 20 circulations, and on average each circulation fading rate 4.2mAh/g, is rear 4 times of circulating for 80 times.

The V of Fig. 6 for making according to embodiment 1 ₂o ₅and V ₂o ₅the high rate performance test result of-GE composite electrode.As seen from the figure, when current density is 200,400,1000mA/g, V ₂o ₅the circulating and reversible specific capacity of-GE composite electrode is 160,129,76mAh/g, and pure V ₂o ₅electrode only has respectively 147,87 and 24mAh/g under the same conditions, after showing that Graphene is compound, and V ₂o ₅nano particle high rate performance has obtained larger improvement.

In order further to explain Graphene, improve V ₂o ₅the essential internal cause of nano particle chemical property, to the V making according to embodiment 1 ₂o ₅nano particle and V ₂o ₅-GE nano composite material electrode has carried out electrochemical impedance test.Fig. 7 is V ₂o ₅and V ₂o ₅the electrochemical impedance figure that-GE nano composite material electrode records.As shown in the figure, V ₂o ₅and V ₂o ₅-GE electrochemistry spectrogram is by the semicircle in medium-high frequency district and the rectilinear(-al) of low frequency range.Than pure V ₂o ₅electrode, V ₂o ₅-GE composite electrode obviously shows less electron transfer resistance, shows V ₂o ₅-GE composite electrode has conductance and electron mobility faster, and this is likely because the structure of high conductivity, high-specific surface area and the porous of Graphene is conducive to the infiltration of electrolyte.

Above-mentioned electrochemical results, has clearly shown V ₂o ₅nano particle appendix, on Graphene, plays an important role to the improvement of its chemical property.V ₂o ₅-GE nano composite anode material has higher reversible specific capacity, better cycle performance and high rate capability, and this may be the result causing due to following reason: first, the high conduction performance of Graphene has improved V ₂o ₅the conductivity of nano particle, for electronics arrives each V from collector ₂o ₅particle surface provides migrating channels; The second, the structure of graphene film porous, is conducive to electrolyte permeability to electrode, the V of nano-scale ₂o ₅shortened Li ⁺migration path; The 3rd, V ₂o ₅good degree of crystallinity has guaranteed reversible phase transformation, simultaneously V ₂o ₅nano particle is dispersed on Graphene, has suppressed the stacking of the reunion of particle and Graphene, and electrode structure in cyclic process is kept.

Should be understood that, above-mentioned example is of the present invention giving an example, although statement is comparatively detailed, can not therefore think the restriction of scope of patent protection of the present invention, and scope of patent protection of the present invention should be as the criterion with claims.

Claims (5)

1. A V ₂ O ₅ nanoparticle/graphene (V ₂ O ₅ -GE) lithium-ion battery cathode material, characterized in that V ₂ O ₅ nanoparticles with a size of 20-40nm are distributed in two-dimensional transparent graphite Alkene sheet-like surface. 2. A method for preparing the V ₂ O ₅ -GE lithium ion battery positive electrode material as claimed in claim 1, characterized in that the specific steps of the method are: A, using the improved Hummer method to synthesize graphite oxide from natural graphite; B. Disperse the graphite oxide powder in N, N-dimethylformamide (DMF), and ultrasonically treat it for 30 minutes to form a stable graphene oxide (GO) dispersion (1 mg/mL); C. Weigh a certain amount of vanadium (IV) acetylacetonate (C ₅ H ₈ O ₂ V) and add it to the GO dispersion in step B, stir for 1 hour to form a uniform and stable solution; D. Transfer the above solution to a hydrothermal kettle and react at 200°C for 20 hours; after cooling to room temperature, centrifuge to collect the black precipitate; wash the obtained precipitate with alcohol and deionized water several times, and dry at 80°C for 6 hours; E. Calcining the dried precipitate at 400° C. for 2 hours with a heating rate of 10° C./min to finally obtain the V ₂ O ₅ -GE lithium ion battery positive electrode material. 3. A method for preparing V ₂ O ₅ -GE lithium-ion battery positive electrode material according to claim 2, characterized in that the solvent medium in which GO is dispersed in step B is DMF. 4 . A method for preparing V ₂ O ₅ -GE lithium ion battery cathode material according to claim 2 , characterized in that the temperature of the hydrothermal reaction in step D is 200° C., and the reaction time is 20 hours. 5. A method for preparing V ₂ O ₅ -GE lithium-ion battery cathode material according to claim 2, characterized in that the black precipitate obtained from the hydrothermal reaction in step E was calcined at 400°C for 2 hours, and the temperature was raised The rate is 10°C/min, and the positive electrode material of V ₂ O ₅ -GE lithium ion battery is obtained.

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