CN111640927A - Graphene-bridged polythiophene-coated germanium nanoparticle composite material and preparation method and application thereof - Google Patents
Graphene-bridged polythiophene-coated germanium nanoparticle composite material and preparation method and application thereof Download PDFInfo
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Abstract
The invention discloses a graphene-bridged polythiophene-coated germanium nanoparticle composite material and a preparation method and application thereof. The preparation method comprises the step of adding neutral GeO2Adding reduced graphene oxide and a dispersing agent into the solution, and pouring NaBH into the solution A4Stirring the solution in water bath to obtain solution B, and high-temperature roasting the precipitate obtained by suction filtration to obtain Ge/RGO compositeFreezing the polythiophene solution, vacuum freeze drying to eliminate water, and vacuum drying at 100-140 deg.c to obtain the composite material for lithium ion battery. The composite material has the advantages of high energy density, good cycling stability, good rate capability, good composite uniformity, easy obtainment of raw materials of the preparation method, simple process, good commercial value and good application prospect.
Description
Technical Field
The invention belongs to the technical field of preparation of composite materials for electrodes, relates to a three-dimensional porous conductive polymer/germanium/carbon composite material, and a preparation method and application thereof, and particularly relates to a graphene bridging polythiophene-coated germanium nanoparticle composite material which can be used as a lithium ion battery cathode material, and a preparation method and application thereof.
Background
With the rapid development of energy storage power sources and electric automobiles, higher requirements are put forward on the performance of lithium ion batteries, and the development of high-energy-density lithium ion batteries becomes a research focus.
Currently commercialized negative electrode materials are mainly carbon materials, and are classified into amorphous carbon and graphitized carbon, wherein the theoretical lithium intercalation capacity of the graphitized carbon is 372mAhg-1Most of the lithium intercalation capacity is distributed between 0.01 and 0.2V (vs. Li)+Li), therefore, the lithium ion battery can provide high and smooth working voltage for the lithium ion battery when being used as a negative electrode material, and is the most applied negative electrode material of the lithium ion battery at present. However, 350mAhg can be achieved due to the actual specific capacity-1Close to the theoretical capacity, the lithium ion battery can not meet the development requirement of the high energy density lithium ion battery. Therefore, how to improve the capacity of the graphite-based negative electrode material is a hot research point of the negative electrode material of the lithium ion battery.
Germanium (Ge) is a group IVA element, and the theoretical mass capacity is as high as 1600mAh g-1The volume specific capacity of the germanium can reach 8500mAh cm when the volume specific capacity exceeds 4 times of the theoretical capacity of the graphite cathode material-3The material has great potential in replacing graphite cathode to become a high-energy density lithium ion battery cathode material. However, the volume change rate of germanium in the process of lithium extraction is as high as 300%, which causes electrode pulverization failure and rapid capacity attenuation, and limits the development of the electrode. How to inhibit pulverization of germanium and improve cycle stability of the germanium is a research hotspot of the high-energy density lithium ion battery cathode material.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a graphene bridged polythiophene-coated germanium nanoparticle composite material which is high in energy density, good in cycling stability, good in rate capability and good in composite uniformity, and a preparation method and application thereof.
In order to solve the technical problems, the invention adopts the following technical scheme.
The graphene-bridged polythiophene-coated germanium nanoparticle composite material mainly comprises germanium nanoparticles, polythiophene and reduced graphene oxide, wherein the polythiophene is coated on the surface of the germanium nanoparticles, the reduced graphene oxide is bridged to the polythiophene coated with the germanium nanoparticles, the germanium nanoparticles account for 70% -98%, the polythiophene accounts for 0.05% -29.95%, the reduced graphene oxide accounts for 0.05% -29.95%, and the sum of the mass fractions of the polythiophene and the reduced graphene oxide is less than or equal to 30%.
Preferably, the germanium nanoparticles are 80-95% of the graphene-bridged polythiophene-coated germanium nanoparticle composite material
Preferably, the particle size of the germanium nanoparticle composite material coated with graphene-bridged polythiophene is 1 nm-50 nm.
Preferably, the polythiophene is a polythiophene with water solubility and conductivity and a polythiophene derivative, and the polythiophene comprises one or more of poly (3, 4-ethylenedioxythiophene) -polystyrene sulfonic acid and a derivative thereof, and polydiethylenedioxythiophene and a derivative thereof.
As a general technical concept, the invention also provides a preparation method of the graphene-bridged polythiophene-coated germanium nanoparticle composite material, which comprises the following steps:
(1) adding GeO2Dissolving in an alkali solution, dropwise adding an acid solution to adjust to neutrality, then adding Reduced Graphene Oxide (RGO) and a dispersing agent, performing ultrasonic oscillation to form a turbid liquid, transferring the turbid liquid into a water bath at 50-60 ℃, and keeping the turbid liquid to be marked as a solution A;
(2) reacting NaBH4Dissolving the powder in water at 1-4 deg.C to obtain NaBH4Pouring the solution into the solution A, and carrying out stirring reaction in a water bath at 50-60 ℃ to obtain a solution B;
(3) carrying out vacuum filtration on the solution B, washing and drying the obtained precipitate, and roasting the precipitate in inert gas or reducing gas at 500-800 ℃ for 0.5-24 h to obtain a Ge/RGO composite material;
(4) adding the Ge/RGO composite material into water, performing ultrasonic dispersion, then adding a polythiophene aqueous solution, performing ultrasonic oscillation, freezing to form a solid, performing vacuum freeze drying at the temperature of-10-0 ℃ to remove moisture, and performing vacuum drying at the temperature of 100-140 ℃ to obtain the graphene bridged polythiophene coated germanium nanoparticle composite material.
Preferably, in the preparation method of the germanium nanoparticle composite material coated with graphene-bridged polythiophene in step (1), the dispersant is GeO20.05-5% of the mass, NaBH in the step (2)4Powder and GeO in the step (1)2The molar ratio of the poly (thiophene) to the poly (thiophene) is 1-20: 1, in the step (4), the polythiophene is a water-soluble and conductive polythiophene and a polythiophene derivative, and the polythiophene comprises one or more of poly (3, 4-ethylenedioxythiophene) -polystyrene sulfonic acid and a derivative thereof, and a polydiethylenedioxythiophene and a derivative thereof.
Preferably, in the preparation method of the germanium nanoparticle composite material coated with graphene-bridged polythiophene in step (1), the dispersant is GeO20.5% -2% of the mass, NaBH in the step (2)4Powder and GeO in the step (1)2The molar ratio of (A) to (B) is 5-10: 1.
Preferably, in the step (1), the alkali solution is a NaOH solution or an ammonia solution, the acid solution is a HCl solution, the dispersant is a water-soluble surfactant, the surfactant includes one or more of polyvinylpyrrolidone, cetyltrimethylammonium bromide, sodium dodecylbenzenesulfonate and sodium carboxymethylcellulose, and the ultrasonic oscillation time is 30-3000 min.
Preferably, in the preparation method of the graphene-bridged polythiophene-coated germanium nanoparticle composite material in step (2), NaBH is used as the carrier4The powder is dissolved in deionized water in an amount to form NaBH4The mass concentration of the solution is controlled to be 1-10%, and the stirring reaction time is 1-24 h.
Preferably, in the preparation method of the graphene-bridged polythiophene-coated germanium nanoparticle composite material, in the step (3), the inert gas is high-purity N2Or Ar gas, the reducing gas is H2And N2Is a mixed gas of either H2And washing with water until the water washing liquid is neutral, wherein the drying is vacuum drying, the temperature of the vacuum drying is 60-100 ℃, and the time of the vacuum drying is 1-12 h.
Preferably, in the step (4), the ultrasonic dispersion time is 20min to 240min, the ultrasonic oscillation time is 20min to 240min, the vacuum freeze-drying time is 2h to 168h, and the vacuum drying time is 1min to 200 min.
As a general technical concept, the invention also provides an application of the graphene-bridged polythiophene-coated germanium nanoparticle composite material or the graphene-bridged polythiophene-coated germanium nanoparticle composite material prepared by the preparation method in a lithium ion battery.
In the present invention, polythiophene is a broad term polythiophene, and includes polythiophene derivatives.
In the preparation method of the invention, GeO2(germanium dioxide) is the source of germanium in the composite material, the invention is about GeO as raw material2GeO is not particularly limited, and may be a common GeO of various origins2。
In the preparation method of the invention, NaOH solution and ammonia water solution are used as main raw materialsIs used for dissolving GeO2Therefore, the concentration thereof is not particularly limited, and the amount is such that the GeO added is completely dissolved2The standard is. Preferably, the NaOH solution has a concentration of 0.5M to 1M, such as 0.8g GeO2Can be dissolved in 40mL0.5M NaOH solution; the concentration of the aqueous ammonia solution is 1M to 5M, such as 0.8g GeO2Can be dissolved in 10mL of 2M aqueous ammonia solution.
In the preparation method of the present invention, the HCl solution is mainly adjusted to a pH of about 7, and the concentration thereof is not particularly limited, and the amount is such that the pH of the solution can be adjusted within the above range. Preferably, the concentration of the HCl solution is between 0.5M and 1M.
In the preparation method, the dispersant mainly has the function of coating the surface of the nano germanium to prevent the nano germanium from agglomerating, and can be polyvinylpyrrolidone, or other water-soluble surfactants such as cetyl trimethyl ammonium bromide, sodium dodecyl benzene sulfonate, sodium carboxymethyl cellulose and the like. The dispersing agent may be added directly to the solution as a solid or as an aqueous dispersion.
In the preparation method of the present invention, the source of the reduced graphene oxide is not particularly limited, and the reduced graphene oxide may be common reduced graphene oxides from various sources, or may be synthesized by itself, and the synthesis method of the reduced graphene oxide is reported in the existing literature, and is not described herein again.
In the preparation method, the high-temperature roasting treatment in the step (3) mainly aims at converting amorphous germanium nanoparticles into crystalline germanium and converting incompletely reduced oxidized germanium into elemental germanium. In order to prevent the germanium from forming oxide at high temperature, inert gas or reducing gas is adopted for protection during roasting, and the inert gas selected by the invention is high-purity N2Or Ar gas, reducing gases generally using H2And N2Mixed gas of (2) or H2And the mixed gas of Ar gas and 5-10% of hydrogen by volume fraction, or pure hydrogen. Preferably, Ar/H is selected2And (4) mixing the gases.
In the preparation method, the conductive polymer polythiophene is preferably PEDOT: PSS, and mainly has the effect of forming a uniform conductive layer polymer on the surface of the nano germanium particles. PEDOT: the source of PSS is not particularly limited, either commercially available or synthesized by itself, and PEDOT, which has a high electronic conductivity, is selected in principle: PSS, preferably PEDOT: the electronic conductivity of the PSS reaches 5S/cm-300S/cm.
In the step (4) of the preparation method, vacuum freeze drying is adopted to remove moisture, and then vacuum drying is carried out at 100-140 ℃, the vacuum freeze drying and vacuum drying combined process can keep a large number of micro-nano gaps formed by nano germanium particles, polythiophene and two-dimensional graphene in the prepared Ge @ PEDOT/RGO composite material and an elastic three-dimensional porous structure skeleton constructed by the micro-nano gaps in the process of removing water, and can also prevent the conditions of PEDOT: the PSS falls off from the surface of the nano germanium particles in the subsequent process of preparing the lithium ion battery pole piece slurry.
In the step (4) of the preparation method of the present invention, reducing graphene oxide, PEDOT: PSS and GeO2The amount of the organic solvent used may be selected according to the composition of the intended anode active material. For example, when GeO2When the using amount is 0.8g and the using amount of the reduced graphene oxide is 0.01g, the ratio of PEDOT: the amount of PSS is 0.03g, the content of germanium nanoparticles in the formed composite material is 93.3%, the content of reduced graphene oxide is about 1.7%, PEDOT: the PSS content is 5.0%. That is, the amount of each compound raw material may be determined by a preset composition of the anode active material, which is also a method conventionally known to those skilled in the art.
Compared with the prior art, the invention has the advantages that:
(1) the invention provides a three-dimensional porous structure lithium ion battery composite negative electrode material Ge @ PEDOT/RGO of Reduced Graphene Oxide (RGO) bridged Polythiophene (PEDOT) coated germanium nanoparticles, wherein a conductive polymer coated outside the germanium nanoparticles is used as a buffer layer and is uniformly dispersed in a three-dimensional conductive network formed by reduced graphene oxide sheet layers, an elastic porous three-dimensional conductive framework of a germanium negative electrode is constructed by combining nano germanium particles, polythiophene coating and two-dimensional graphene, the high-strength conductive framework can be effectively maintained, and the problem of collapse and damage of the conductive structure caused by germanium powdering is solved.
The invention compounds the nano structures with different dimensions to form a large amount of micro-nano-scale gaps, can well buffer and resolve stress strain generated by volume change, and can separate germanium nano particles to prevent electrochemical activity reduction caused by agglomeration. The elastic porous conductive framework constructed by combining the nano germanium particles, the polythiophene coating and the two-dimensional graphene can maintain higher strength and keep the integrity of the framework in the charging and discharging processes, and simultaneously improve the capacity and the cycle performance of the germanium material. The structural design of the invention can utilize the flexibility of the polythiophene to buffer the stress generated by the volume expansion of the germanium nano particles coated by the polythiophene, and simultaneously, the polythiophene can play a role in improving the problems of low electronic conductivity and the like of the germanium, thereby being beneficial to improving the rate capability of the cathode. The invention also adopts a zero-dimensional nano structure of the polythiophene with the germanium nano particles coated by the soft two-dimensional graphene in a bridging manner, and can construct a three-dimensional porous conductive network communicated with the inside from the space, thereby providing a complete main body conductive framework for the electrochemical circulation of the germanium active substances. The structural design of the composite material can obviously improve the effects of the composite material as a lithium ion battery cathode material in the aspects of energy density, cycle stability, rate capability and the like.
(2) The preparation method has the advantages of easily obtained raw materials and simple process, the composite material prepared by the method has a three-dimensional porous structure of the reduced graphene oxide bridged polythiophene-coated germanium nanoparticles, the uniformity and the stability of the structure are far higher than those of the common physical mixing method, the composite material has high capacity, the structure is stable, agglomeration does not occur, and therefore the lithium ion battery has higher durability and cycling stability.
(3) The composite material obtained by the preparation method has good processability, is easy to be fully mixed and dispersed with a conductive agent and the like, and is beneficial to implementation of subsequent preparation processes of negative electrode slurry and negative electrode plates.
In the preparation method, the germanium nanoparticles are synthesized in situ, the functional groups on the reduced graphene oxide can provide active sites for the formation of the germanium nanoparticles, and meanwhile, the soft two-dimensional structure of the reduced graphene oxide also has the function of preventing the nano germanium particles from agglomerating, thereby being beneficial to controlling the nano germanium particles in the nano scale. Compared with a physical mixing method, the method for in-situ synthesis of the nano germanium particles in the reduced graphene oxide dispersion liquid greatly improves the compounding uniformity of the nano germanium and the reduced graphene oxide. The high-temperature roasting reduction process not only converts the germanium from the amorphous state to the crystalline state, but also completely reduces the incompletely reduced germanium oxide in the liquid phase to the elemental state, improves the content of elemental germanium in the composite material system, and is beneficial to improving the reversible capacity of the cathode material system.
In the step (4) of the preparation method, vacuum freeze drying is adopted to remove moisture, and then vacuum drying is carried out at 100-140 ℃, the vacuum freeze drying and vacuum drying combined process can keep a large number of micro-nano gaps formed by nano germanium particles, polythiophene and two-dimensional graphene in the prepared Ge @ PEDOT/RGO composite material and an elastic three-dimensional porous structure skeleton constructed by the micro-nano gaps in the process of removing water, and can also prevent the conditions of PEDOT: the PSS falls off from the surface of the nano germanium particles in the subsequent process of preparing the lithium ion battery pole piece slurry, and the step is very important for improving the cycle performance and the rate capability of the negative electrode material. In addition, the method combining vacuum freeze drying and vacuum drying can prevent the composite material from hard agglomeration and agglomeration, improve the processability of the composite material, is easy to be fully mixed and dispersed with a conductive agent and the like, and is beneficial to implementation of the subsequent preparation process of the negative electrode slurry and the negative electrode plate.
(3) In the preparation method of the present invention, high-conductivity PEDOT: the PSS is used as a raw material, so that on one hand, the conductivity of a negative electrode material system is increased, and on the other hand, the content of PEDOT: PSS has a strong hydrophilicity, while the nano-germanium surface is also hydrophilic and its hydrophilicity is stronger than that of reduced graphene oxide, and thus, based on the interaction of hydrophilic groups, PEDOT: PSS is easier to form a uniform coating layer on the surface of the nano germanium particles and form a bridging structure of the nano germanium particles and the coating layer, so that the cycling stability and the rate capability of the cathode material are improved.
Drawings
Fig. 1 is a schematic structural diagram of a graphene-bridged polythiophene-coated germanium nanoparticle composite material in example 1 and example 2 of the present invention.
Detailed Description
The invention is further described below with reference to the drawings and specific preferred embodiments of the description, without thereby limiting the scope of protection of the invention.
The materials and equipment used in the following examples are commercially available. The unit M is mol/L.
Example 1:
the graphene-bridged polythiophene-coated germanium nanoparticle composite material mainly comprises germanium nanoparticles, polythiophene and reduced graphene oxide, wherein the polythiophene is coated on the surface of the germanium nanoparticles, and the reduced graphene oxide is bridged to the polythiophene coated with the germanium nanoparticles, as shown in fig. 1. The polythiophene is in particular poly (3, 4-ethylenedioxythiophene) -polystyrene sulfonic acid, abbreviated to PEDOT: PSS, the content of germanium nanoparticles is about 93.3% by mass, PEDOT: the content of PSS is 5.0%, and the content of reduced graphene oxide is about 1.7%.
In this embodiment, the germanium nanoparticles have a particle size of 1nm to 50 nm.
The preparation method of the graphene-bridged polythiophene-coated germanium nanoparticle composite material comprises the following steps:
(1) 40mL of a 0.5M NaOH solution was added to a 500mL beaker, and 0.8g of GeO was added2Stirring until the solution is dissolved, then dropwise adding 0.5M HCl solution to adjust the solution to be neutral, namely pH is about 7.0, then adding 0.01g of reduced graphene oxide into the mixed solution, then adding 0.02g of polyvinylpyrrolidone, carrying out ultrasonic oscillation for 60 minutes to form uniform turbid liquid, transferring the turbid liquid into a water bath at 60 ℃, and keeping the turbid liquid to be recorded as a solution A.
(2) 2.4g of NaBH4And completely dissolving the powder into 80mL of deionized water at 1-4 ℃, quickly pouring the powder into the solution A, and stirring the solution in a water bath at 60 ℃ for 3 hours to obtain a solution B.
(3) Vacuum filtering the solution B, washing the obtained precipitate with deionized water until the water washing solution is neutral, and vacuum drying at 100 ℃ for 12 h. And then placing the dried solid into a tubular furnace to be roasted for 5 hours in an argon-hydrogen mixed atmosphere (hydrogen content is 5%) at the temperature of 600 ℃, and cooling to obtain the Ge/RGO composite material which is powdery solid.
(4) Adding the prepared Ge/RGO composite material into 20mL of deionized water, performing ultrasonic dispersion for 120min to uniformly disperse the Ge/RGO composite material, then adding an aqueous solution containing 0.03g of poly (3, 4-ethylenedioxythiophene) -polystyrene sulfonic acid (PEDOT: PSS (PH1000)), performing ultrasonic oscillation for 240min, freezing the mixture into a solid in a freezer of a refrigerator, performing vacuum freeze drying at the temperature of minus 5 ℃ until the moisture is completely removed (about 96h is needed), and performing vacuum drying in a vacuum drying oven at the temperature of 100 ℃ for 30min after the moisture is removed to obtain the graphene bridged polythiophene-coated germanium nanoparticle composite material which is marked as Ge @ PEDOT/RGO composite material.
The graphene-bridged polythiophene-coated germanium nanoparticle composite material prepared in the embodiment is applied to a lithium ion battery as a lithium ion battery cathode material, and the process is as follows:
the Ge @ PEDOT/RGO composite material prepared in the embodiment 1 is used as a lithium ion battery negative electrode material and is respectively mixed with acetylene black serving as a conductive agent and a bonding agent LA133 according to the mass ratio of 80: 10, wherein the bonding agent LA133 adopts an aqueous solution with the solid content of 5%. And (3) preparing the prepared mixture into slurry, uniformly coating the slurry on a copper foil, and performing vacuum drying at 100-120 ℃ for 24 hours to obtain the pole piece for the experimental battery. LiPF with lithium sheet as counter electrode and electrolyte of 1mol/L6The solution, the solvent is EC (ethyl carbonate) + DMC (dimethyl carbonate) (volume ratio 1: 1), the diaphragm is celgard2400 membrane, and the CR2025 button cell is prepared in a glove box filled with argon atmosphere.
Through tests, the charge-discharge cycle performance of the button cell made of the Ge @ PEDOT/RGO composite material prepared in the embodiment 1 is as follows: the first discharge specific capacity is 1120mAh/g, and the discharge specific capacity is 880mAh/g after 200 times of circulation. The first discharge specific capacity of the Ge @ PEDOT/RGO negative electrode material (composite material) is 1400mAh/g, and the discharge specific capacity after 200 times of circulation is 1100 mAh/g.
The Ge @ PEDOT/RGO composite material prepared in the embodiment 1 has the following characteristics:
the embodiment compounds the nano structures with different dimensions to form a large amount of micro-nano-scale gaps, can well buffer and digest stress strain generated by volume change, and can separate germanium nano particles to prevent electrochemical activity reduction caused by agglomeration. The elastic porous conductive framework can maintain higher strength and keep the integrity of the framework in the charge-discharge process, and simultaneously improve the capacity and the cycle performance of the germanium material. The structural design of the invention can utilize the flexibility of the polythiophene to buffer the stress generated by the volume expansion of the germanium nano particles coated by the polythiophene, and simultaneously, the polythiophene can play a role in improving the problems of low electronic conductivity and the like of the germanium, thereby being beneficial to improving the rate capability of the cathode. The invention also adopts a zero-dimensional nano structure of the polythiophene with the germanium nano particles coated by the soft two-dimensional graphene in a bridging manner, and can construct a three-dimensional porous conductive network communicated with the inside from the space, thereby providing a complete main body conductive framework for the electrochemical circulation of the germanium active substances. The structural design of the composite material can obviously improve the effects of the composite material as a lithium ion battery cathode material in the aspects of energy density, rate capability, cycle stability and the like.
In addition, the composite material prepared by the preparation method disclosed by the invention does not agglomerate due to hard agglomeration, has good processability, is easy to be fully mixed and dispersed with a conductive agent and the like, and is beneficial to implementation of subsequent preparation processes of negative electrode slurry and a negative electrode plate.
From the above, the lithium ion battery negative electrode material prepared in this embodiment 1 shows high capacity and stable cycle performance, and has a good commercial value and a wide application prospect, compared with the commercial graphite negative electrode material.
Example 2
The graphene-bridged polythiophene-coated germanium nanoparticle composite material mainly comprises germanium nanoparticles, polythiophene and reduced graphene oxide, wherein the polythiophene is coated on the surface of the germanium nanoparticles, and the reduced graphene oxide is bridged to the polythiophene coated with the germanium nanoparticles, as shown in fig. 1. The polythiophene is specifically poly (3, 4-ethylenedioxythiophene) -polystyrene sulfonic acid PEDOT: PSS, the content of germanium nanoparticles is about 81.0% by mass, PEDOT: the content of PSS is 14.6%, and the content of reduced graphene oxide is about 4.4%.
In this embodiment, the germanium nanoparticles have a particle size of 1nm to 50 nm.
The preparation method of the graphene-bridged polythiophene-coated germanium nanoparticle composite material comprises the following steps:
(1) a500 mL beaker was charged with 40mL of a 0.5M aqueous ammonia solution, and 0.8g of GeO was added2Stirring until dissolved, and then adding 0.5M HCl solution dropwise to adjust the pH of the solution to about 7.0. And adding 0.03g of reduced graphene oxide into the obtained solution, adding 0.02g of polyvinylpyrrolidone, carrying out ultrasonic oscillation for 60 minutes to form uniform turbid liquid, and transferring the turbid liquid into a water bath at 60 ℃ to be recorded as a solution A.
(2) 2.4g of NaBH4And dissolving the powder into 80mL of deionized water at 1-4 ℃, then quickly pouring the powder into the solution A, and stirring the solution in a water bath at 60 ℃ for 3 hours to obtain a solution B.
(3) Vacuum filtering the solution B, washing the precipitate with deionized water until the water washing solution is neutral, and vacuum drying at 100 deg.C for 12 hr. And (3) placing the dried solid into a tubular furnace, roasting for 5 hours at 600 ℃ in an argon-hydrogen mixed atmosphere (hydrogen content is 5%), and cooling to obtain the Ge/RGO composite material.
(4) Adding the prepared Ge/RGO composite material into 20mL of deionized water, performing ultrasonic dispersion for 120min to uniformly disperse the Ge/RGO composite material, then adding an aqueous solution containing 0.1g of poly (3, 4-ethylenedioxythiophene) -polystyrene sulfonic acid (PEDOT: PSS (PH1000)), performing ultrasonic oscillation for 120min, freezing the mixture into a solid in a freezer of a refrigerator, performing vacuum freeze drying at the temperature of minus 2 ℃ until the moisture is completely removed (about 72h), and performing vacuum drying in a vacuum drying oven at the temperature of 120 ℃ for 5min after the moisture is removed to obtain the graphene bridged polythiophene-coated germanium nanoparticle composite material which is marked as Ge @ PEDOT/RGO composite material.
The graphene-bridged polythiophene-coated germanium nanoparticle composite material prepared in the embodiment is applied to a lithium ion battery as a lithium ion battery cathode material, and the process is as follows:
the lithium ion battery negative electrode material obtained in the embodiment is respectively mixed with conductive agent acetylene black and a binder LA133 according to the mass ratio of 80: 10, wherein the binder LA133 adopts an aqueous solution with the solid content of 5%, the mixture is prepared into slurry, the slurry is uniformly coated on a copper foil, and the slurry is dried in vacuum at 100-120 ℃ for 24 hours to prepare the pole piece for the experimental battery. A lithium plate is used as a counter electrode, an electrolyte is a 1mol/L LiPF6 solution, a solvent is EC (ethyl carbonate) + DMC (dimethyl carbonate) (the volume ratio is 1: 1), a diaphragm is a celgard2400 membrane, and the CR2025 button cell is prepared in a glove box filled with argon atmosphere.
Through tests, the charge-discharge cycle performance of the button cell made of the lithium ion battery cathode material prepared in the embodiment 2 is as follows: the first discharge specific capacity is 850mAh/g, and the discharge specific capacity is 790mAh/g after 200 times of circulation. The first discharge specific capacity of the Ge @ PEDOT/RGO negative electrode material is 1062mAh/g, and the discharge specific capacity after 200 times of circulation is 987 mAh/g.
As can be seen from the above, the negative electrode material for lithium ion battery prepared in example 2 exhibited high capacity and stable cycle performance relative to the commercial graphite negative electrode material.
The foregoing is merely a preferred embodiment of the invention and is not intended to limit the invention in any manner. Although the present invention has been described with reference to the preferred embodiments, it is not intended to be limited thereto. Those skilled in the art can make many possible variations and modifications to the disclosed embodiments, or equivalent modifications, without departing from the spirit and scope of the invention, using the methods and techniques disclosed above. Therefore, any simple modification, equivalent replacement, equivalent change and modification made to the above embodiments according to the technical essence of the present invention are still within the scope of the protection of the technical solution of the present invention.
Claims (10)
1. The graphene-bridged polythiophene-coated germanium nanoparticle composite material is characterized by mainly comprising germanium nanoparticles, polythiophene and reduced graphene oxide, wherein the polythiophene is coated on the surface of the germanium nanoparticles, the reduced graphene oxide is bridged to the polythiophene coated with the germanium nanoparticles, the germanium nanoparticles account for 70% -98%, the polythiophene accounts for 0.05% -29.95%, the reduced graphene oxide accounts for 0.05% -29.95%, and the sum of the mass fractions of the polythiophene and the reduced graphene oxide is less than or equal to 30%.
2. The graphene-bridged polythiophene-coated germanium nanoparticle composite material of claim 1, wherein the germanium nanoparticles are 80% -95% and/or the particle size of the germanium nanoparticles is 1 nm-50 nm.
3. The graphene-bridged polythiophene-coated germanium nanoparticle composite material according to claim 1 or 2, wherein the polythiophene is a polythiophene with water solubility and conductivity and a polythiophene derivative, and the polythiophene comprises one or more of poly (3, 4-ethylenedioxythiophene) -polystyrene sulfonic acid and a derivative thereof, and polyethylenedioxythiophene and a derivative thereof.
4. A preparation method of the graphene-bridged polythiophene-coated germanium nanoparticle composite material as claimed in any one of claims 1-3, comprising the following steps:
(1) adding GeO2Dissolving in an alkali solution, dropwise adding an acid solution to adjust to neutrality, then adding Reduced Graphene Oxide (RGO) and a dispersing agent, performing ultrasonic oscillation to form a turbid liquid, transferring the turbid liquid into a water bath at 50-60 ℃, and keeping the turbid liquid to be marked as a solution A;
(2) reacting NaBH4Dissolving the powder in water at 1-4 deg.C to obtain NaBH4Pouring the solution into the solution A, and carrying out stirring reaction in a water bath at 50-60 ℃ to obtain a solution B;
(3) carrying out vacuum filtration on the solution B, washing and drying the obtained precipitate, and roasting the precipitate in inert gas or reducing gas at 500-800 ℃ for 0.5-24 h to obtain a Ge/RGO composite material;
(4) adding the Ge/RGO composite material into water, performing ultrasonic dispersion, then adding a polythiophene aqueous solution, performing ultrasonic oscillation, freezing to form a solid, performing vacuum freeze drying at the temperature of-10-0 ℃ to remove moisture, and performing vacuum drying at the temperature of 100-140 ℃ to obtain the graphene bridged polythiophene coated germanium nanoparticle composite material.
5. The method for preparing the graphene-bridged polythiophene-coated germanium nanoparticle composite material according to claim 4, wherein the dispersant is GeO in the step (1)20.05-5% of the mass, NaBH in the step (2)4Powder and GeO in the step (1)2The molar ratio of the poly (thiophene) to the poly (thiophene) is 1-20: 1, in the step (4), the polythiophene is a water-soluble and conductive polythiophene and a polythiophene derivative, and the polythiophene comprises one or more of poly (3, 4-ethylenedioxythiophene) -polystyrene sulfonic acid and a derivative thereof, and a polydiethylenedioxythiophene and a derivative thereof.
6. The method for preparing the graphene-bridged polythiophene-coated germanium nanoparticle composite material according to claim 5, wherein in the step (1), the mass of the dispersant is GeO20.5% -2% of the mass, NaBH in the step (2)4Powder and GeO in the step (1)2The molar ratio of (A) to (B) is 5-10: 1.
7. The preparation method of the graphene-bridged polythiophene-coated germanium nanoparticle composite material according to any one of claims 4-6, wherein in the step (1), the alkali solution is a NaOH solution or an ammonia water solution, the acid solution is a HCl solution, the dispersing agent is a water-soluble surfactant, the surfactant comprises one or more of polyvinylpyrrolidone, cetyltrimethylammonium bromide, sodium dodecylbenzenesulfonate and sodium carboxymethylcellulose, and the ultrasonic oscillation time is 30-3000 min;
in the step (2), the NaBH4Dissolving the powder in deionized water to removeAmount of ionized water to form NaBH4The mass concentration of the solution is controlled to be 1-10%, and the stirring reaction time is 1-24 h.
8. The method for preparing the graphene-bridged polythiophene-coated germanium nanoparticle composite material according to any one of claims 4 to 6, wherein in the step (3), the inert gas is high-purity N2Or Ar gas, the reducing gas is H2And N2Is a mixed gas of either H2And washing with water until the water washing liquid is neutral, wherein the drying is vacuum drying, the temperature of the vacuum drying is 60-100 ℃, and the time of the vacuum drying is 1-12 h.
9. The preparation method of the graphene-bridged polythiophene-coated germanium nanoparticle composite material according to any one of claims 4-6, wherein in the step (4), the ultrasonic dispersion time is 20-240 min, the ultrasonic oscillation time is 20-240 min, the vacuum freeze-drying time is 2-168 h, and the vacuum drying time is 1-200 min.
10. Application of the graphene-bridged polythiophene-coated germanium nanoparticle composite material as defined in any one of claims 1 to 3 or the graphene-bridged polythiophene-coated germanium nanoparticle composite material prepared by the preparation method as defined in any one of claims 4 to 9 in a lithium ion battery.
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