CN108899473B - High-performance flexible lithium secondary battery positive electrode and preparation method thereof - Google Patents

High-performance flexible lithium secondary battery positive electrode and preparation method thereof Download PDF

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CN108899473B
CN108899473B CN201810615441.0A CN201810615441A CN108899473B CN 108899473 B CN108899473 B CN 108899473B CN 201810615441 A CN201810615441 A CN 201810615441A CN 108899473 B CN108899473 B CN 108899473B
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CN108899473A (en
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李朝晖
宋学霞
李继成
肖启振
雷钢铁
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Xiangtan University
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
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    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
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    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H01M4/1391—Processes of manufacture of electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
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    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/628—Inhibitors, e.g. gassing inhibitors, corrosion inhibitors
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Abstract

The invention discloses a high-performance flexible lithium secondary battery anode, wherein the anode material is sodium vanadate nanobelt/reduced graphene oxide nanosheet Na5V12O32The composite film of/RGO, wherein the length of sodium vanadate nano-belt is 100-300 μm, the width is 0.1-1 μm, the thickness is 8-27nm, the flexible composite film does not need to be loaded on the aluminum foil current collector, can be assembled with lithium foil into a high-energy lithium secondary battery, and can normally work after being folded and wound for many times. The invention also discloses a preparation method of the high-performance flexible lithium secondary battery anode, which adopts simple vacuum filtration Na5V12O32The method for preparing the mixed suspension of the nanobelts and the RGO nanosheets has the advantages that the flexible electrode which can be folded and bent for use is prepared, the process is simple, and the industrial production is easy to realize. The flexible electrode prepared by the invention has excellent electrochemical performance and is an ideal positive electrode for assembling a high-energy-density flexible lithium secondary battery.

Description

High-performance flexible lithium secondary battery positive electrode and preparation method thereof
Technical Field
The invention relates to the field of electrochemistry, in particular to a positive electrode material-sodium vanadate nanobelt/reduced graphene oxide (Na) of a flexible lithium secondary battery5V12O32an/RGO) composite electrode film and a preparation method thereof.
Background
At present, although lithium ion batteries have occupied a certain position in the electronic consumer market and have further improved energy and power density, the application of lithium ion batteries in the field of electric vehicles has old shortcomings, and with the development of advanced portable electronic devices, the demand of human beings for portable energy sources is higher and higher.
Lithium metal has a theoretical specific capacity of 3860mAh/g, and the energy density of a lithium secondary battery assembled with it as a negative electrode far exceeds that of a lithium ion battery assembled with a carbon negative electrode. However, most of the layered oxide positive electrode materials LiCoO2,LiNi1-x-yCoxMnyO2,LiFePO4The theoretical specific capacity of the alloy is generally not more than 200 mAh/g; layered lithium-rich manganese-based positive electrode material Li1.2Mn0.54Co0.13Ni0.13O2Although the specific capacity is as high as 300mAh/g, the problems of low coulombic efficiency, poor rate capability and cycle performance and the like for the first time restrict the industrial use of the composite material.
With the trend that more and more electronic devices gradually turn to be light, thin and flexible, development of foldable energy storage products with high energy density is a current research hotspot. Therefore, increasing the energy density of the positive electrode material is one of the currently significant challenges facing lithium secondary batteries.
In the article (charaterization of commercial available lithium-ion batteries, Journal of Power Sources,1998,70(1): 48-50), it is proposed that in commercial lithium ion batteries, the aluminum foil current collector accounts for 15% of the mass of the entire positive electrode and the copper foil current collector accounts for 40% of the mass fraction of the entire negative electrode. Aluminum foil and copper foil are non-electrochemically active materials and cannot provide electric capacity, which greatly reduces the energy density of the lithium ion battery, but are indispensable as electron conductive current collectors. Therefore, the development of a new lightweight current collector has been the goal of many researchers in recent years. The flexible electrode is assembled by the high-energy-density anode material and the novel light current collector, and the flexible electrode becomes the current research focus. Because of the conductivity and lightweight property of carbon materials, carbon nanotubes or graphene are often used to prepare new lightweight current collectors to meet the requirements of electronic devices for lightness, thinness and flexibility.
As a lithium ion battery anode material, vanadium oxide shows high specific capacity due to the changeable valence (+2 to +5) and more embedding sites. Wherein, the layer V is2O5When the material is used as a positive electrode electrochemical active substance, the material has the theoretical capacity of 440mAh/g, but the rate capability and the cycle performance are still poor. And sodium vanadate (Na) in lamellar form5V12O32) As one of the vanadium oxide classes, having a structure other than V2O5The unique layered structure of the material, namely: sodium ion pre-intercalated in V3O8Between crystal layers, it plays the role of skeleton support to make Na5V12O32The crystal structure of the material in the charging and discharging (lithium ion insertion-extraction) process is stable, and the cycle performance of the material is improved; the spacing between the material layers supported by sodium ions is enlarged, which is beneficial to Li+The rate capability of the material is improved. But 10-2Electronic conductivity of S/cm and 10-10cm2s-1Grade of Li+Ion diffusion coefficient, not enough to allow Na5V12O32The requirement of rapid charge and discharge is met.
As is known, the nano material has huge specific surface area and extremely short ion diffusion distance, and under the condition that the lithium ion diffusion coefficient is so low, the electrode material is synthesized into the nano-scale size, so that the solid phase transition time of lithium ions in the material can be effectively shortened. The synthesized nano material is compounded with an electronic conducting material to accelerate the transfer of electrons, so that lithium ions and electrons can be simultaneously provided on an electrode material [ Chen C.C., Maier J., domestic electronics and ion storage and the path from interfacial storage to specific electrodes, Nature Energy,2018,3:102-108 ], thereby improving the rapid charge and discharge capacity of the electrode material. The one-dimensional nano material (nanowire, nanofiber, nanorod, nanobelt and the like) and the two-dimensional nano material (nanosheet) are compounded to obtain the flexible electrode material with good mechanical property, and the electrode does not need a metal current collector, a conductive agent and a binder, so that the energy density of the electrode is greatly improved, the manufacturing cost of the electrode is reduced, and the electrode is worthy of vigorous development and popularization.
Therefore, the research on a high-performance flexible lithium secondary battery positive electrode and a preparation method thereof is a problem that needs to be solved urgently by those skilled in the art.
Disclosure of Invention
In view of the above, the present invention provides a high-performance flexible lithium secondary battery positive electrode.
In order to achieve the purpose, the invention adopts the following technical scheme:
the high-performance flexible lithium secondary battery anode is characterized by being formed by compounding a sodium vanadate nanobelt and reduced graphene oxide, wherein the sodium vanadate nanobelt and the reduced graphene oxide are interwoven into a flexible electrode film, and the molecular formula of sodium vanadate is Na5V12O32，An electrochemically active substance Na in the flexible electrode film5V12O32The mass fraction of (A) is 91-96%.
Preferably, the length of the sodium vanadate nanoribbon is 100-300 μm, the width is 0.1-1 μm, and the thickness is 8-27 nm.
By adopting the technical scheme, the invention has the following beneficial effects:
1. the graphene serving as a novel conductive material can greatly improve the electronic conductivity of the material compared with other conductive materials; increasing the contact area of the composite material; further improving the mechanical strength of the composite material.
2. Film-like Na5V12O32On one hand, the/RGO composite structure removes the binder, and the electrochemical active substance is directly compounded with the graphene, so that the electron transfer resistance of the electrode material is reduced, the dissolution of the electrode material in the electrolyte is also inhibited, and the electrochemical performance of the electrode film is improved. The interlaced membrane material is beneficial to the permeation of electrolyte, accelerates the diffusion rate of lithium ions and improves the rate capability of the electrode membrane.
3. Film-like Na5V12O32the/RGO composite structure can buffer the volume expansion and contraction of the material in the charge and discharge processThe change of the electrode film plays a good role in protection, and prevents the materials from agglomerating in the circulation process, thereby further improving the circulation performance of the electrode film.
4. Film-like Na5V12O32the/RGO composite structure is compared with Na without composite graphene5V12O32The electrode film and the composite electrode film have greatly improved mechanical properties and better flexibility, and can still recover to the previous state after being bent without unrecoverable deformation.
The invention further discloses a preparation method of the high-performance flexible lithium secondary battery anode.
In order to achieve the purpose, the invention adopts the following technical scheme:
a preparation method of a high-performance flexible lithium secondary battery anode comprises the following specific steps:
step one, preparing reduced graphene oxide RGO
Adding graphene oxide GO into deionized water, and performing ultrasonic dispersion for 7-8 hours to obtain brown turbid liquid;
adding sodium hydroxide into the suspension, stirring, transferring the suspension into a hydrothermal reaction kettle lined with polytetrafluoroethylene for reaction, cooling to room temperature to obtain black suspension, wherein the mass ratio of the sodium hydroxide to the graphene oxide GO is 1: 20-30;
performing suction filtration, washing filter residues obtained through suction filtration with deionized water to be neutral, then washing with alcohol, and finally blending with ethanol to obtain a suspension of primarily Reduced Graphene Oxide (RGO) in ethanol;
step two, preparing sodium vanadate nanobelts
Weighing vanadium pentoxide powder, adding 0.02M oxalic acid solution, and stirring for 05-1h to obtain a blue solution; the ratio of the vanadium pentoxide powder to the 0.02M oxalic acid solution is 1: 0.2-0.3.
Then adding sodium salt, continuously stirring, transferring the mixed solution into a hydrothermal reaction kettle lined with polytetrafluoroethylene for reaction, and cooling to obtain nano-banded sodium vanadate Na5V12O32The material, the precipitate,dispersing and washing by using distilled water;
then carrying out suction filtration, dispersing the solution by using distilled water to obtain a suspension, finally adding a certain proportion of aminopropyltriethoxysilane APTES, and carrying out ultrasonic treatment for 30min to obtain a sodium vanadate suspension with the concentration of 17mg/mL, wherein the proportion of the propyltriethoxysilane APTES to 0.02M oxalic acid solution is 16.5-33.5: 1;
step three, preparing Na5V12O32RGO precursor
Weighing the prepared RGO and sodium vanadate suspension according to the volume ratio of 1:10-20 of the RGO and sodium vanadate suspension, mixing, and ultrasonically stirring for 20-40min to obtain Na5V12O32The mixed solution of/RGO is filtered by suction to obtain membranous Na5V12O32an/RGO composite material;
then drying in a vacuum drying oven to obtain membranous Na5V12O32a/RGO precursor;
step four, preparation of Na5V12O32/RGO composite electrode film
The membrane Na obtained in the third step5V12O32Placing the/RGO precursor in a tubular atmosphere furnace, introducing inert gas, slowly heating and calcining in a sectional manner, and slowly cooling along with the furnace to obtain flexible Na5V12O32an/RGO composite electrode film.
By adopting the preparation process, the invention has the beneficial effects that:
according to the invention, graphene oxide is selected as a raw material, and Reduced Graphene Oxide (RGO) is obtained after hydrothermal reaction, so that a plurality of defects are generated on the surface of the RGO, the RGO can be uniformly dispersed in a solution, and the RGO can be well compounded with a synthesized nanobelt material.
Preferably, the hydrothermal reaction conditions in the first step are as follows: the reaction time is 10-24h, and the reaction temperature is 120-200 ℃.
Preferably, the sodium salt in the second step is one of sodium nitrate, sodium sulfate, sodium chloride or sodium acetate, and the aminopropyltriethoxysilane APTES is a surface modifier with the model of KH 550.
Preferably, the hydrothermal reaction conditions in the second step are as follows: the reaction time is 8-15h, and the reaction temperature is 160-240 ℃.
Preferably, Na in step four5V12O32The sectional slow temperature rise calcining mode of the/RGO precursor comprises the following steps: firstly, heating to 280 ℃ in the air at the speed of 0.2 ℃/min, and keeping for 3 h; then heating to 400 ℃ at the speed of 0.2 ℃/min in nitrogen, sintering for 3h, and slowly cooling to room temperature along with the furnace.
Preferably, in the fourth step, the drying temperature of the flexible composite electrode film is 50-80 ℃.
Preferably, the content of the reduced graphene oxide RGO in the flexible composite electrode film obtained in the fourth step is 0 to 15%.
Preferably, the content of reduced graphene oxide RGO in the flexible composite electrode film obtained in the fourth step is 9%.
According to the technical scheme, compared with the prior art, the invention has the following beneficial effects: the invention discloses a preparation method of a high-performance flexible lithium secondary battery anode, which comprises the steps of firstly preparing Reduced Graphene Oxide (RGO) and sodium vanadate nanobelts by a hydrothermal method, and then compounding the prepared RGO and the sodium vanadate nanobelts to obtain Na5V12O32a/RGO precursor, and finally calcining Na in an inert atmosphere5V12O32The RGO precursor can further carbonize the graphene oxide GO which is not reduced in the precursor, and the crystallinity of the sodium vanadate nanobelt is improved to obtain Na5V12O32an/RGO composite electrode film. According to the invention, the reduced graphene oxide RGO and the sodium vanadate nanobelt are prepared by adopting a hydrothermal method, so that well-crystallized powder can be directly obtained without high-temperature firing treatment, powder agglomeration possibly formed in the firing process is avoided, the process is simple, and the controllability is strong. And after hydrothermal treatment, Na is filtered by simple vacuum filtration5V12O32The method for preparing the mixed suspension of the nanobelts and the RGO nanosheets prepares the flexible electrode which can be folded and bent for use, has simple process and is easy to manufactureAnd (5) industrial production.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.
FIG. 1 is an XRD spectrum and a refined spectrum of a sodium vanadate nanoribbon electrode film prepared by the method.
FIG. 2 shows pure Na5V12O32Electrode film, Na5V12O32A 4% RGO composite electrode film and Na5V12O32XRD spectrum of/9% RGO composite electrode film.
Fig. 3 is an SEM photograph of an electrode film prepared according to the present invention;
FIG. 4 shows Na5V12O32TEM photographs of the/9% RGO composite electrode film.
FIG. 5 shows the preparation of pure Na according to the invention5V12O32Electrode film, Na5V12O32A 4% RGO composite electrode film and Na5V12O32First charge and discharge curves of the/9% RGO composite electrode film at a current density of 35 mA/g.
FIG. 6 shows Na5V12O32Charge and discharge curves of the/9% RGO composite electrode film under different discharge rates.
FIG. 7 shows Na prepared according to the present invention5V12O32Cycle performance curve of/9% RGO composite electrode film at 5C magnification.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The embodiment of the invention discloses a high-performance flexible lithium secondary battery anode which is formed by compounding a sodium vanadate nanobelt and reduced graphene oxide, wherein the sodium vanadate nanobelt and the reduced graphene oxide are interwoven into a flexible electrode film, and the molecular formula of sodium vanadate is Na5V12O32An electrochemically active substance Na in the flexible electrode film5V12O32The mass fraction of (A) is 91-96%.
Preferably, the length of the sodium vanadate nanoribbon is 100-300 μm, the width is 0.1-1 μm, and the thickness is 8-27 nm.
The invention discloses a preparation method of a high-performance flexible lithium secondary battery anode.
A preparation method of a high-performance flexible lithium secondary battery anode comprises the following specific steps:
step one, preparing reduced graphene oxide RGO
Adding graphene oxide GO into deionized water, and performing ultrasonic dispersion for 7-8 hours to obtain brown turbid liquid;
adding sodium hydroxide into the suspension, stirring, transferring the suspension into a hydrothermal reaction kettle lined with polytetrafluoroethylene for reaction, cooling to room temperature to obtain black suspension, wherein the mass ratio of the sodium hydroxide to the graphene oxide GO is 1: 20-30;
performing suction filtration, washing filter residues obtained through suction filtration with deionized water to be neutral, then washing with alcohol, and finally blending with ethanol to obtain a suspension of primarily Reduced Graphene Oxide (RGO) in ethanol, wherein the concentration is 3.3 mg/mL;
step two, preparing sodium vanadate nanobelts
Weighing vanadium pentoxide powder, adding 0.02M oxalic acid solution, and stirring for 05-1h to obtain a blue solution; the ratio of the vanadium pentoxide powder to the 0.02M oxalic acid solution is 1: 0.2-0.3.
Preferably, the ratio between the vanadium pentoxide powder and the 0.02M oxalic acid solution is specifically 1: 0.275.
Then adding sodium salt to continueStirring, transferring the mixed solution into a hydrothermal reaction kettle lined with polytetrafluoroethylene for reaction, and cooling to obtain nano-banded sodium vanadate Na5V12O32The material is precipitated and is dispersed and washed by distilled water;
then carrying out suction filtration, dispersing by using distilled water to obtain a suspension, finally adding a certain proportion of aminopropyltriethoxysilane APTES, and carrying out ultrasonic treatment for 30min to obtain a sodium vanadate suspension with the concentration of 17mg/mL, wherein the proportion of the propyltriethoxysilane APTES to 0.02M oxalic acid solution is 16.5-33.5: 1.
Step three, preparing Na5V12O32RGO precursor
Weighing the prepared RGO and sodium vanadate suspension according to the volume ratio of 1:10-20 of the RGO and sodium vanadate suspension, mixing, and ultrasonically stirring for 20-40min to obtain Na5V12O32The mixed solution of/RGO is filtered by suction to obtain membranous Na5V12O32an/RGO composite material;
then drying in a vacuum drying oven to obtain membranous Na5V12O32a/RGO precursor;
step four, preparation of Na5V12O32/RGO composite electrode film
The membrane Na obtained in the third step5V12O32Placing the/RGO precursor in a tubular atmosphere furnace, introducing inert gas, slowly heating and calcining in a sectional manner, and slowly cooling along with the furnace to obtain flexible Na5V12O32an/RGO composite electrode film.
Preferably, the hydrothermal reaction conditions in the first step are as follows: the reaction time is 10-24h, and the reaction temperature is 120-200 ℃.
Preferably, the sodium salt in the second step is one of sodium nitrate, sodium sulfate, sodium chloride or sodium acetate, and the aminopropyltriethoxysilane APTES is a surface modifier with the model of KH 550.
Preferably, the hydrothermal reaction conditions in the second step are as follows: the reaction time is 8-15h, and the reaction temperature is 160-240 ℃.
Preferably, the hydrothermal reaction conditions in step two are as follows: the reaction time is 12h, and the reaction temperature is 200 ℃.
Preferably, Na in step four5V12O32The sectional slow temperature rise calcining mode of the/RGO precursor comprises the following steps: firstly, heating to 280 ℃ in the air at the speed of 0.2 ℃/min, and keeping for 3 h; then heating to 400 ℃ at the speed of 0.2 ℃/min in nitrogen, sintering for 3h, and slowly cooling to room temperature along with the furnace.
Preferably, in the fourth step, the drying temperature of the flexible composite electrode film is 50-80 ℃.
Preferably, in the fourth step, the drying temperature of the flexible composite electrode film is 60 ℃.
Preferably, the content of the reduced graphene oxide RGO in the flexible composite electrode film obtained in the fourth step is 0 to 15%.
Preferably, the content of reduced graphene oxide RGO in the flexible composite electrode film obtained in the fourth step is 9%.
The present invention will be further described with reference to specific examples.
Example 1:
a preparation method of a high-performance flexible lithium secondary battery anode comprises the following specific steps:
step one, adding 100mg of graphene oxide GO into a beaker filled with 100mL of deionized water, and performing ultrasonic dispersion for 8 hours to obtain 1mgmL-1The brown suspension of (4); adding 4g of sodium hydroxide NaOH into the suspension, quickly stirring the suspension for 2h, adding the suspension into a 200mL hydrothermal reaction kettle with a polytetrafluoroethylene lining, reacting for 18h at 160 ℃, cooling to room temperature to obtain black suspension, washing filter residue obtained by suction filtration to be neutral by using deionized water, washing the filter residue by using alcohol, and finally blending by using alcohol to obtain a suspension of primarily reduced graphene oxide RGO in the alcohol, wherein the concentration of the suspension is 3.3 mg/mL;
step two, weighing 1g of vanadium pentoxide (V)2O5) The powder was placed in a beaker and 100mL of 0.02 oxalic acid (H) was added2C2O4) The solution was stirred for 1h to give a blue solution, then 1.06g of NaNO was added3Stirring for 30min, and transferring the mixed solution to 200mL of hydrothermal reaction kettle with polytetrafluoroethylene lining, reacting at 200 ℃ for 12h, and cooling to obtain nano-banded sodium vanadate Na5V12O32Dispersing and washing the precipitate by distilled water, then performing suction filtration, dispersing by distilled water to obtain a suspension, and finally adding a certain proportion of aminopropyltriethoxysilane APTES for ultrasonic treatment for 30min to obtain a sodium vanadate suspension with the concentration of 17 mg/mL;
step three, weighing the prepared 4mL RGO suspension and 60mL sodium vanadate suspension (wherein the mass ratio of RGO to sodium vanadate is 9: 91) according to the proportion, mixing, and ultrasonically stirring for 30min to obtain Na5V12O32The mixed solution of/RGO is filtered by suction to obtain membranous Na5V12O32the/RGO composite material is then placed in a vacuum drying oven to be dried at 60 ℃ to obtain membranous Na5V12O32a/RGO precursor;
step four, Na obtained in the step three is used5V12O32Placing the/RGO precursor in a tubular atmosphere furnace, introducing nitrogen, slowly heating and calcining in a sectional manner, and slowly cooling along with the furnace to obtain flexible Na5V12O32A/RGO composite membrane. After thermogravimetric analysis, the electrochemical active substance Na in the electrode film5V12O32Is 91% by mass.
To prove the Na produced by the invention5V12O32the/RGO composite electrode film has good effect, and the invention is further verified.
Na prepared in example 15V12O32the/RGO composite electrode membrane is cut into a circular sheet with the diameter of 12mm, the circular sheet is used as a positive electrode, a lithium negative electrode and a Celgard 2400 porous membrane are assembled into a button battery, and the electrolyte is 1mol/L LiPF6Ethylene Carbonate (EC) and dimethyl carbonate (DMC) solutions (mass ratio of both 1: 1).
The button cell is tested by using a constant current charging and discharging technology, the testing temperature is 25 ℃, the charging termination voltage is 4V, and the discharging termination voltage is 1.5V. When the mixture is charged at 0.1C (35mA/g), 0.2C, 0.5C, 1C, 2C, 5C and 10CDischarge capacities at discharge were 331, 308, 270, 233, 197, 158 and 121mAh/g, respectively, corresponding to 52.7, 49.0, 43.1, 37.1, 31.3, 25.2 and 19.3mAh/cm, respectively3The volume to capacity ratio of; the capacity retention rate after 500 cycles of charging and discharging at 5C rate was 93.7%.
Example 2
Na was synthesized by the method of example 1 while changing the content of graphene5V12O32an/RGO composite electrode film. After thermogravimetric analysis, the electrochemical active substance Na in the electrode film5V12O32The mass fraction of (2) is 96%.
Na was measured in the same manner as in example 15V12O32Electrochemical performance of the/RGO composite material. In the voltage range of 1.5-4.0V, the lithium ion battery is charged and discharged at the multiplying power of 0.1C, 0.2C, 0.5C, 1C, 2C, 5C and 10C, the first discharge specific capacity is 311, 285, 251, 211, 183, 132 and 84mAh/g respectively, and is respectively corresponding to 49.5, 45.4, 40.0, 33.6, 29.0, 21.0 and 13.4mAh/cm3Volume to capacity of (a). Under the 2C multiplying power, after the cycle is 200 times, the discharge specific capacity retention rate is 93.5%.
For examples 1-2 of the present invention, further analysis will be made with reference to the drawings attached to the specification.
In example 1, an electrochemically active material Na in an electrode film5V12O32Is 91 percent;
in example 2, the electrochemically active material Na in the electrode film5V12O32The mass fraction of (2) is 96%.
As shown in fig. 1, fig. 1 is an XRD spectrum and a fine modification spectrum of the sodium vanadate nanobelt electrode film prepared in example 1 of the present invention.
As can be seen from the figure, the synthesized sodium vanadate nanobelt has Na5V12O32The crystal structure of (1), the lattice parameters are:
Figure BDA0001696632010000111
106.56 ° containing about 5% NaV3O8Phase, characteristic diffraction peak of main phase andthe XRD standard card PDF #24-1156 is basically consistent and belongs to P121/m1 space group, with higher crystallinity.
To further demonstrate the effect of the present invention, the present invention was directed to pure Na5V12O32Electrode film, Na5V12O32A 4% RGO composite electrode film and Na5V12O32Three/9% RGO composite electrode films were compared, as shown in FIG. 2, where FIG. 2 is pure Na5V12O32Electrode film, Na5V12O32A 4% RGO composite electrode film and Na5V12O32XRD spectrum of/9% RGO composite electrode film. As can be seen from FIG. 2, Na5V12O32the/RGO composite electrode film has the same structure as the pure Na5V12O32XRD characteristic diffraction peak positions similar to electrode films, due to RGO wrapping, attributed to Na5V12O32The intensity of each characteristic peak of (a) is slightly decreased. Since RGO is calcined at a lower temperature, is difficult to highly graphitize, is substantially amorphous carbon, and its content in the electrode film is low, a characteristic diffraction peak to which RGO belongs does not appear on the XRD spectrum.
Fig. 3 is an SEM photograph of an electrode film prepared by the present invention.
Wherein, a in FIG. 3&c is pure Na prepared by the invention5V12O32SEM photograph of the electrode film. As can be seen from the figure, Na5V12O32The material has the one-dimensional nanoribbon shape, the length is 100-300 mu m, the width is 0.1-1 mu m, the nanoribbons are mutually interwoven into an electrode film, and obvious porous structures are arranged among the nanoribbons.
B in FIG. 3&d is Na prepared by the invention5V12O32SEM pictures of/9% RGO composite electrode films. As can be seen from the figure, Na5V12O32The nanobelts are wrapped in the RGO nanosheets, and the morphology remains intact.
FIG. 4 shows Na5V12O32TEM photograph of/9% RGO composite electrode film, as can be seen from FIG. 4, Na5V12O32The nanobelts are uniformly dispersed in the RGO matrixThe thickness is 8-27 nm.
FIG. 5 shows the preparation of pure Na according to the invention5V12O32Electrode film, Na5V12O32A 4% RGO composite electrode film and Na5V12O32First charge and discharge curves of the/9% RGO composite electrode film at a current density of 35 mA/g. As can be seen from the figure, the initial charge/discharge capacities of the three are 295/300, 305/311 and 326/331mAh/g respectively, the first discharge capacity is slightly larger than the charge capacity, which shows that a very small amount of lithium ions inserted into the crystal during the discharge process are not extracted and are retained in the crystal lattice, which is beneficial to the stability of the crystal structure, thereby improving the cycle performance of the electrode.
FIG. 6 shows Na5V12O32Charge and discharge curves of the/9% RGO composite electrode film under different discharge rates. As can be seen from FIG. 6, the discharge capacities at 0.1C (35mA/g), 0.2C, 0.5C, 1C, 2C, 5C and 10C were 331, 308, 270, 233, 197, 158 and 121mAh/g, respectively, which are 52.7, 49.0, 43.1, 37.1, 31.3, 25.2 and 19.3mAh/cm, respectively3The specific volume capacity of the composite material is high, and the composite material has excellent rate performance.
FIG. 7 shows Na prepared according to the present invention5V12O32Cycle performance curve of/9% RGO composite electrode film at 5C magnification. As can be seen from fig. 7, after 500 cycles, the capacity retention rate was 93.7%, and the cycle performance was excellent.
Example 3
Weighing 1g of vanadium pentoxide (V)2O5) Placing the powder in a beaker, adding 0.02M oxalic acid (H)2C2O4) The solution was stirred for 1 hour at 100mL to obtain a blue solution, and then 1.06g of NaNO was added3Stirring for 30min, transferring the mixed solution into a 200mL hydrothermal reaction kettle with a polytetrafluoroethylene lining, reacting at 200 ℃ for 12h, and cooling to obtain nano-banded sodium vanadate Na5V12O32A material. Washing the precipitate with distilled water, filtering, and dispersing with distilled water to obtain suspension with solid-to-liquid ratio of 17 mg/mL. 4mL of aminopropyltriethoxysilane KH550 was added to the obtained suspension, and the mixture was subjected to ultrasonic treatment for 30 minutes to obtain a sodium vanadate suspension. Filtering under reduced pressure to extract the filtrate on filter paperThe cake was dried in vacuo at 50 ℃ for 12 h. Putting the dried filter cake into a tubular atmosphere furnace, heating to 280 ℃ at the speed of 0.2 ℃/min in the air atmosphere, and preserving heat for 3 hours; then heating to 400 ℃ at the speed of 0.2 ℃/min in nitrogen atmosphere, sintering for 3h, and slowly cooling along with the furnace to obtain nano-belt-shaped Na5V12O32A woven electrode film.
Na was measured in the same manner as in example 15V12O32Electrochemical properties of the electrode film. In the voltage range of 1.5-4.0V, the lithium ion battery is charged and discharged at the multiplying power of 0.1C, 0.2C, 0.5C, 1C, 2C, 5C and 10C, the first discharge specific capacity is 300mAh/g, 267, 203, 152, 115, 58 and 20mAh/g respectively, and is respectively corresponding to 47.7, 42.6, 32.3, 24.2, 18.3, 9.2 and 3.2mAh/cm3Volume to capacity of (a). Under the 2C multiplying power, after the cycle is 200 times, the discharge specific capacity retention rate is 76.5%.
The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other. The device disclosed by the embodiment corresponds to the method disclosed by the embodiment, so that the description is simple, and the relevant points can be referred to the method part for description.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (8)

1. The high-performance flexible lithium secondary battery anode is characterized by being formed by compounding sodium vanadate nanobelts and reduced graphene oxide, wherein the sodium vanadate nanobelts and the reduced graphene oxide are interwoven into a flexible electrode film, and the vanadic acid isThe molecular formula of sodium is Na5V12O32An electrochemically active substance Na in the flexible electrode film5V12O32The mass fraction of (A) is 91-96%;
the high-performance flexible lithium secondary battery positive electrode is prepared by the following steps:
step one, preparing reduced graphene oxide RGO
Adding graphene oxide GO into deionized water, and performing ultrasonic dispersion for 7-8 hours to obtain brown turbid liquid;
adding sodium hydroxide into the suspension, stirring, transferring the suspension into a hydrothermal reaction kettle lined with polytetrafluoroethylene for reaction, cooling to room temperature to obtain black suspension, wherein the mass ratio of the sodium hydroxide to the graphene oxide GO is 1: 20-30;
performing suction filtration, washing filter residues obtained through suction filtration with deionized water to be neutral, then washing with alcohol, and finally blending with ethanol to obtain a suspension of primarily Reduced Graphene Oxide (RGO) in ethanol;
step two, preparing sodium vanadate nanobelts
Weighing vanadium pentoxide powder, adding 0.02M oxalic acid solution, and stirring for 0.5-1h to obtain a blue solution; the mass volume ratio of the vanadium pentoxide powder to the 0.02M oxalic acid solution is 1g to 100 ml;
then adding sodium salt, continuously stirring, transferring the mixed solution into a hydrothermal reaction kettle lined with polytetrafluoroethylene for reaction, and cooling to obtain nano-banded sodium vanadate Na5V12O32The material is precipitated and is dispersed and washed by distilled water;
then carrying out suction filtration, dispersing the solution by using distilled water to obtain a suspension, and finally adding gamma-aminopropyltriethoxysilane to carry out ultrasonic treatment for 30min to obtain a sodium vanadate suspension, wherein the volume ratio of the gamma-aminopropyltriethoxysilane to a 0.02M oxalic acid solution is 4: 100;
step three, preparing Na5V12O32RGO precursor
Weighing the prepared RGO and sodium vanadate suspension according to the volume ratio of 1:10-20 of the RGO and sodium vanadate suspension, mixing, and ultrasonically stirring for 20-40min to obtain the final productNa5V12O32The mixed solution of/RGO is filtered by suction to obtain membranous Na5V12O32an/RGO composite material;
then drying in a vacuum drying oven to obtain membranous Na5V12O32a/RGO precursor;
step four, preparation of Na5V12O32/RGO composite electrode film
The membrane Na obtained in the third step5V12O32Placing the/RGO precursor in a tubular atmosphere furnace, introducing inert gas, slowly heating and calcining in a sectional manner, and slowly cooling along with the furnace to obtain flexible Na5V12O32an/RGO composite electrode film;
na in the fourth step5V12O32The sectional slow temperature rise calcining mode of the/RGO precursor comprises the following steps: firstly, heating to 280 ℃ in the air at the speed of 0.2 ℃/min, and keeping for 3 h;
then heating to 400 ℃ at the speed of 0.2 ℃/min in nitrogen, sintering for 3h, and slowly cooling to room temperature along with the furnace.
2. The positive electrode of claim 1, wherein the sodium vanadate nanoribbon has a length of 100-300 μm, a width of 0.1-1 μm, and a thickness of 8-27 nm.
3. The positive electrode of claim 1, wherein the hydrothermal reaction conditions in the first step are as follows: the reaction time is 10-24h, and the reaction temperature is 120-200 ℃.
4. The positive electrode of claim 1, wherein the sodium salt in step two is one of sodium nitrate, sodium sulfate, sodium chloride and sodium acetate.
5. The positive electrode of claim 1, wherein the hydrothermal reaction conditions in the second step are as follows: the reaction time is 8-15h, and the reaction temperature is 160-240 ℃.
6. The positive electrode of claim 1, wherein the drying temperature of the flexible composite electrode film in the fourth step is 50-80 ℃.
7. The positive electrode of claim 1, wherein the content of Reduced Graphene Oxide (RGO) in the flexible composite electrode film obtained in the fourth step is 4-9%.
8. The positive electrode of claim 7, wherein the content of Reduced Graphene Oxide (RGO) in the flexible composite electrode film obtained in the fourth step is 9%.
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