阅读说明：本技术 一种氮掺杂碳/石墨烯/硅自支撑体复合电极的制备方法 (Preparation method of nitrogen-doped carbon/graphene/silicon self-supporting composite electrode ) 是由 易旭 于 2019-10-24 设计创作，主要内容包括：本发明公开了一种氮掺杂碳/石墨烯/硅自支撑体复合电极的制备方法,该方法是将纳米硅粉、聚丙烯腈及氧化石墨烯分散液加入到强极性有机溶剂中,加热搅拌至聚丙烯腈溶解,得到混合溶液；所得混合溶液倒入模具内,在常温下静置处理后,置于震动环境中,同时向模具内缓慢加入醇类溶剂,析出聚丙烯腈与氧化石墨烯共包覆纳米硅复合物,复合物经过真空干燥及热处理,即得氮掺杂碳/石墨烯/硅自支撑体复合电极,该复合电极放电比容量高,电化学循环稳定性好,且不需要再添加导电剂、粘结剂等电化学惰性物质,也不需要集流体,减轻了电极的重量,工艺流程简单,易实施并适合规模化生产。(The invention discloses a preparation method of nitrogen-doped carbon/graphene/silicon self-supporting body composite electrodes, which comprises the steps of adding nano silicon powder, polyacrylonitrile and graphene oxide dispersion liquid into a strong-polarity organic solvent, heating and stirring until the polyacrylonitrile is dissolved to obtain a mixed solution, pouring the obtained mixed solution into a mold, standing at normal temperature, placing the mold in a vibration environment, slowly adding an alcohol solvent into the mold to separate out a polyacrylonitrile and graphene oxide co-coated nano silicon compound, and carrying out vacuum drying and heat treatment on the compound to obtain the nitrogen-doped carbon/graphene/silicon self-supporting body composite electrode.)

The preparation method of the nitrogen-doped carbon/graphene/silicon self-supporting body composite electrode is characterized by comprising the following steps:

1) adding nano silicon powder, polyacrylonitrile and graphene oxide dispersion liquid into a strong-polarity organic solvent, heating and stirring until polyacrylonitrile is dissolved to obtain a mixed solution;

2) pouring the mixed solution into a mold, and standing at normal temperature;

3) placing the mold after standing treatment in a vibration environment, and slowly adding an alcohol solvent into the mold to separate out a polyacrylonitrile and graphene oxide co-coated nano silicon compound;

4) and (3) carrying out vacuum drying and heat treatment on the polyacrylonitrile and graphene oxide co-coated nano silicon composite to obtain the nitrogen-doped carbon/graphene/silicon self-supporting body composite electrode.

2. The method for preparing the nitrogen-doped carbon/graphene/silicon self-supporting composite electrode according to claim 1, wherein the method comprises the following steps:

the particle size range of the nano silicon powder is 10 nm-100 nm;

the concentration of the graphene oxide dispersion liquid is 0.01 mg/mL-2 mg/mL;

the strong polar organic solvent is DMSO or DMF.

The mass percentage content of carbon in the polyacrylonitrile is 40-60%.

3. The method for preparing the nitrogen-doped carbon/graphene/silicon self-supporting composite electrode according to claim 1 or 2, wherein the method comprises the following steps:

the mass ratio of the nano silicon powder to the polyacrylonitrile is 0.25-4: 1;

the volume ratio of the strong polar organic solvent to the graphene oxide dispersion liquid is 5-10: 1.

4. The method for preparing the nitrogen-doped carbon/graphene/silicon self-supporting composite electrode according to claim 1, wherein the method comprises the following steps: the heating and stirring temperature is 100-150 ℃, and the time is 0.5-1 h.

5. The method for preparing the nitrogen-doped carbon/graphene/silicon self-supporting composite electrode according to claim 1, wherein the method comprises the following steps: and the standing time at the normal temperature is 0.2-2 h.

6. The method for preparing the nitrogen-doped carbon/graphene/silicon self-supporting composite electrode according to claim 1, wherein the method comprises the following steps: the alcohol solvent is 1-8 times of the volume of the mixed solution in the mold.

7. The method for preparing the nitrogen-doped carbon/graphene/silicon self-supporting composite electrode according to claim 6, wherein the method comprises the following steps: the alcohol solvent is methanol.

8. The method for preparing the nitrogen-doped carbon/graphene/silicon self-supporting composite electrode according to claim 1, wherein the method comprises the following steps: the heat treatment process comprises the following steps: at 1-5 ℃ for min^-1Heating to 210-220 ℃ at a heating rate, preserving heat for 1-3 hours, and then heating for 1-5 ℃ for min^-1The temperature is raised to 500-750 ℃ at the heating rate, and the temperature is kept for 1-6 h.

9. The method for preparing the nitrogen-doped carbon/graphene/silicon self-supporting composite electrode according to claim 8, wherein the method comprises the following steps: the heat treatment is carried out under a protective atmosphere.

Technical Field

The invention relates to a preparation method of lithium ion battery composite electrodes, in particular to a preparation method of nitrogen-doped carbon/graphene/silicon self-supporting composite electrodes, and belongs to the technical field of lithium battery materials.

Background

The lithium ion battery has the characteristics of high voltage, high specific energy, long cycle life, environmental friendliness and the like, and becomes an ideal matching power supply for portable electronic products, mobile products and electric vehicles. Due to the rapid development of portable electronic devices, mobile products and electric vehicles, novel lithium ion batteries with high energy density and high specific capacity are urgently needed, and the development of novel lithium ion battery cathode materials is critical. The theoretical capacity of the traditional graphite cathode is only 372mAh g^-1The development of the whole lithium ion battery industry is severely restricted. The silicon (Si) cathode material has the advantages of high theoretical capacity, low discharge platform, abundant resources, good safety performance and the like, and the theoretical capacity can reach 3579mAh g^-1 kinds of electrode materials are very possible to replace the commercial graphite cathode, therefore, the silicon-based materials are receiving more and more attention from researchers as the cathode of the lithium ion battery.

However, the drastic change of the crystal lattice of the Si negative electrode material in the charge and discharge processes hinders the use of pure Si: in Li⁺In view of the above problems, researchers have explored various methods for improving the cycle performance of silicon negative electrode materials, such as reducing the particle size of silicon materials, forming porous materials, silicon thin film materials, silicon nanowires, silicon composites, etc., wherein a relatively efficient method is to prepare silicon-based composites to mitigate volume expansion during charging and discharging, and this method has been widely used in the research on modification of lithium ion battery negative electrode materials.

Chinese patent (publication No. CN109713265A) discloses lithium ion battery silicon-carbon cathode materials and a preparation method thereof, wherein a nickel simple substance and/or a nickel-containing compound is/are used as a catalyst to carry out catalytic carbonization on a material coated with silicon by polyacrylate, so that the expansion of the silicon material can be effectively relieved, and the cycle performance of the battery material is improved.

Chinese patent (publication No. CN106941164A) discloses a preparation method of silicon-carbon cathode core-shell materials, wherein amorphous carbon and graphene are adopted to coat silicon particles, the conductivity of a battery material and the cycle performance of a battery are improved in degree, but the method cannot well protect pulverization of nano silicon particles and falling of active substances under the condition of high cycle times.

The method can not fundamentally solve the problem of rapid volume expansion of the silicon material cathode lithium ion battery in the charging and discharging processes.

Disclosure of Invention

The invention aims to provide a preparation method of nitrogen-doped carbon/graphene/silicon self-supporting body composite electrodes, aiming at solving the technical problems of the existing silicon negative electrode of a lithium battery, the composite electrodes prepared by the method have a structure that silicon nano particles are coated by nitrogen-doped carbon and graphene composite carbon materials, and the problem of rapid volume expansion of the silicon material negative electrode lithium ion battery in the charging and discharging processes can be well solved, so that the charging and discharging performance and the multiplying power performance of the silicon negative electrode lithium ion battery are improved, the service life is prolonged, meanwhile, the composite electrodes have a supporting body structure which is jointly constructed by the nitrogen-doped carbon and the graphene, and the supporting body and the silicon nano particles are compounded in situ, so that the electrochemical cycle stability of the electrodes is greatly improved, electrochemical inert substances such as a conductive agent, a binder and the like do not need to be added, a current collector is also not needed, the weight of the electrodes is reduced.

In order to achieve the technical purpose, the invention provides a preparation method of nitrogen-doped carbon/graphene/silicon self-supporting composite electrodes, which comprises the following steps:

1) adding nano silicon powder, polyacrylonitrile and graphene oxide dispersion liquid into a strong-polarity organic solvent, heating and stirring until polyacrylonitrile is dissolved to obtain a mixed solution;

2) pouring the mixed solution into a mold, and standing at normal temperature;

3) placing the mold after standing treatment in a vibration environment, and slowly adding an alcohol solvent into the mold to separate out a polyacrylonitrile and graphene oxide co-coated nano silicon compound;

4) and (3) carrying out vacuum drying and heat treatment on the polyacrylonitrile and graphene oxide co-coated nano silicon composite to obtain the nitrogen-doped carbon/graphene/silicon self-supporting body composite electrode.

In a preferable scheme, the particle size range of the nano silicon powder is 10 nm-100 nm. The more preferable particle size range is 10nm to 70 nm; most preferably 20 to 50 nm.

Preferably, the concentration of the graphene oxide dispersion liquid is 0.01 mg/mL-2 mg/mL. A more preferred concentration is 0.5mg/mL to 2 mg/mL. Most preferably 1 mg/L.

In a preferred embodiment, the strongly polar organic solvent is dimethyl sulfoxide (DMSO) or N-Dimethylformamide (DMF). Most preferred is DMSO. The polyacrylonitrile can be well dissolved by the preferred polar organic solvent.

In a preferred scheme, the carbon content percentage content of the polyacrylonitrile is 40-60%. The more preferred percentage of carbonaceous material is from 45% to 55%.

In the preferable scheme, the mass ratio of the nano silicon powder to the polyacrylonitrile is 0.25-4: 1. The preferable mass ratio is 0.5 to 3: 1.

In the preferable scheme, the volume ratio of the strong polar organic solvent to the graphene oxide dispersion liquid is 5-10: 1;

in a preferable scheme, the heating and stirring temperature is 100-150 ℃, and the time is 0.5-1 h. The heating and stirring temperature is preferably 100 to 130 ℃ and the time is preferably 0.5 to 1 hour.

In a preferred scheme, the standing time at the normal temperature is 30-120 minutes. The preferable standing time at normal temperature is 40min to 80 min. The mixed solution can be cooled to room temperature by standing at normal temperature, and the mixed solution is uniform without raw material separation.

According to the invention, the dispersion state of the nano silicon particles and the graphene can be ensured by adopting vibration, and the alcohol precipitation rate of polyacrylonitrile can be improved.

In the preferable scheme, the volume of the alcohol solvent is 1-8 times of that of the mixed solution in the mold. More preferably 2 to 4 times of the volume of the mixed solution in the mold.

In a preferred embodiment, the alcohol solvent is methanol.

Preferably, the heat treatment process comprises: at 1-5 ℃ for min^-1Heating to 210-220 ℃ at a heating rate, preserving heat for 1-3 hours, and then heating for 1-5 ℃ for min^-1The temperature is raised to 500-750 ℃ at the heating rate, and the temperature is kept for 1-6 h. The preferable heat treatment time is 1 to 3 hours.

Preferably, the heat treatment is performed under a protective atmosphere. A protective atmosphere such as nitrogen or an inert atmosphere.

The die is designed according to the size and the shape of the electrode plate. The diameter of the die is 0.5 cm-2.0 cm.

The vibration of the invention can be realized by adopting a small vibration pump. The vibration time range is 15-30 h.

The alcohol solvent of the present invention is added by dropwise addition.

The temperature range of the vacuum drying oven is 50-80 ℃.

Compared with the prior art, the technical scheme of the invention has the following beneficial technical effects:

according to the technical scheme, the characteristics that polyacrylonitrile can be dissolved in a strong-polarity organic solvent and can be separated out in low-carbon alcohol are fully utilized, the graphene, the nano silicon particles and the polypropylene dissolving solution are mixed into a uniform mixed solution, the polyacrylonitrile is separated out in situ by using an alcohol separation principle, so that the nano silicon particles and the graphene material are uniformly dispersed in a polyacrylonitrile resin matrix, -step high-temperature carbonization and shaping are carried out, the polyacrylonitrile generates nitrogen-doped carbon in situ, a support body structure jointly constructed by the nitrogen-doped carbon and the graphene is obtained, the nano silicon particles are uniformly coated in the support body structure jointly constructed by the nitrogen-doped carbon and the graphene, the technical problem that the nano silicon particles are easy to expand in volume and fall off in the charging and discharging processes is solved, meanwhile, the prepared electrode has a self-support body structure, the electrode preparation process is simplified, and the cost is saved.

The composite electrode prepared by the invention has a structure that the silicon nano-particles are coated by the nitrogen-doped carbon and graphene composite carbon material, and can better solve the problem of rapid volume expansion of a silicon material negative lithium ion battery in the charging and discharging processes, so that the charging and discharging performance and the rate capability of the silicon negative lithium ion battery are improved, the service life is prolonged, meanwhile, the composite electrode has a support body structure jointly constructed by the nitrogen-doped carbon and the graphene, and the support body and the silicon nano-particles are compounded in situ, so that the electrochemical cycle stability of the electrode is greatly improved, and electrochemical inert substances such as a conductive agent, a binder and the like do not need to be added in the preparation process, and a current collector is not needed, so that the weight of the electrode is reduced, and the composite electrode has.

The nitrogen-doped carbon/graphene/silicon self-supporting composite electrode prepared by the method has excellent high rate capability, such as 5A g^-1The reversible capacity under the current density is up to 763mAh g^-1. When the current density is restored to 0.2A g^-1The specific capacity of the composite material is about 1750mAh g^-1. At 5A g^-1The battery capacity still maintains about 701.4mAh g after 800 cycles under the current density^-1The specific capacity of the resin is high, and the resin has excellent cycle performance.

Description of the drawings:

fig. 1 is an SEM electron micrograph of the nitrogen-doped carbon/graphene/silicon self-supporting composite electrode material prepared in example 1 of the present invention.

FIG. 2 shows a composite electrode with a 0.5Ag layer and a nitrogen-doped carbon/graphene/silicon self-supporting body prepared in example 1 of the present invention^-1Cycling performance curve at current density.

Fig. 3 is a rate performance curve of the nitrogen-doped carbon/graphene/silicon self-supporting composite electrode prepared in example 1 of the present invention at different current densities.

Detailed Description

While the following is a description of the preferred embodiments of the present invention, it should be noted that those skilled in the art can make various modifications and improvements without departing from the principle of the embodiments of the present invention, and such modifications and improvements are considered to be within the scope of the embodiments of the present invention.