CN109301187B

CN109301187B - Carbon-coated SnO applied to lithium ion battery cathodexPreparation method of quantum dot/graphene composite

Info

Publication number: CN109301187B
Application number: CN201811056972.7A
Authority: CN
Inventors: 胡毅; 沈桢
Original assignee: Zhejiang Sci Tech University ZSTU
Current assignee: Zhejiang Sci Tech University ZSTU
Priority date: 2018-09-11
Filing date: 2018-09-11
Publication date: 2021-12-03
Anticipated expiration: 2038-09-11
Also published as: CN109301187A

Abstract

The invention relates to carbon-coated SnO applied to a lithium ion battery cathode_xA preparation method of a quantum dot/graphene composite. The method comprises the following steps: (1) preparation of a solution to be irradiated: (2) irradiation: placing the solution to be irradiated obtained in the step (1) under an excimer light source for irradiation, and stirring simultaneously; (3) carbon coated SnO_xPreparing a quantum dot/graphene composite: subjecting the product obtained in step (2) to reaction in H₂Calcining in the atmosphere of/Ar mixed gas to prepare the carbon-coated SnO_xA quantum dot/graphene composite. The preparation method is simple, short in flow and high in efficiency. The carbon coating layer not only effectively disperses SnO_xQuantum dots, and can be used as SnO_xThe volume change generated in the charging and discharging process plays a role in inhibiting, and electrons can be accelerated in SnO_xMigration of the quantum dot surface layer. Such carbon-coated SnO_xThe quantum dot/graphene composite can be used as a negative electrode material of a lithium ion battery and a sodium ion battery.

Description

Carbon-coated SnO applied to lithium ion battery cathodexPreparation method of quantum dot/graphene composite

Technical Field

The invention relates to the field of energy storage system device materials, in particular to carbon-coated SnO applied to a lithium ion battery cathode_xA preparation method of a quantum dot/graphene composite.

Background

With the development of social production and the improvement of economic life in the 21 st century, environmental and energy problems become increasingly prominent. The human craving for new energy is more and more urgent, and the search for developing green sustainable energy and energy technology has become a research hotspot in the world today. The development of energy and the research of energy technology necessarily involve energy conversion and energy storage. At present, the development and utilization level of renewable energy sources are rapidly advanced by human beings, however, in order to further utilize the renewable energy sources with obvious intermittence such as solar energy, wind energy, tidal energy and the like, a proper high-efficiency energy storage device is required to be equipped. Chemical power sources are novel high-efficiency energy technology devices for converting chemical energy into electric energy, and are widely researched and rapidly developed in recent decades. And the chemical power source capable of working circularly, namely the secondary battery, meets the increasing demands of people. At present, the secondary batteries on the market mainly include lead-acid batteries, nickel-cadmium batteries, nickel-hydrogen batteries and lithium ion batteries.

The lithium ion battery has the advantages of high working voltage, large energy density, long cycle life, environmental protection, no pollution and the like, and is widely applied to production and life as an efficient energy storage device. The negative electrode material is one of the key elements determining the performance of the lithium ion battery. Most of the currently commercialized negative electrodes are carbon-based materials with high electrochemical stability, but the lower theoretical capacity (e.g. 372mAh/g graphite) of the carbon-based materials cannot meet the requirement of high-capacity usability of the energy storage device.

The content of tin on the earth crust is high, the source is rich, the tin-based material has higher theoretical capacity, the theoretical capacity of simple substance tin is 990mAh/g, and tin dioxide (SnO)₂) The theoretical capacity is 1494 mAh/g. However, SnO is involved in the intercalation/deintercalation of lithium ions during charging/discharging₂The volume expansion/contraction of nearly 300 percent can be generated, so that the powder, the fragment and the shedding of the powder are caused, on one hand, the electric contact between an active substance and a current collector is influenced, the electron transmission is not facilitated, and the capacity of the battery is rapidly attenuated; on the other hand, a Solid Electrolyte Interface (SEI) formed between the active material and the electrolyte is continuously thickened, so that the cycle performance of the battery is rapidly reduced.

There are many ways to solve the above problem, which can be summarized as the following points: (1) introducing a support material (such as carbon material, metal oxide) with SnO₂Mixing, embedding or coating, etc.; (2) reduction of SnO₂Particle size to reduce volume effects; (3) design of synthetically Stable SnO₂Spatial geometry (e.g., hollow spheres, hollow cubes, etc.). A number of novel SnO structures therefrom₂Base materials such as zero-dimensional nanoparticles, one-dimensional nanowires, two-dimensional nanoplates, and the like. Among them, the zero-dimensional nanoparticles have the best mechanical stability due to their isotropic spherical structure. However, the nanoparticles have large specific surface area, high surface energy and easy agglomeration, which leads to reduced electrical contact, especially for smaller SnO₂Quantum dots, agglomerate very severely.

The graphene has larger specific surface area due to the unique two-dimensional structure, and SnO₂The quantum dots are deposited on the graphene, so that SnO can be prevented₂And (4) agglomeration of the quantum dots. Moreover, the high conductivity of graphene greatly improves SnO₂The electron transfer rate of the surface of the quantum dot is improved, so that the electrochemical performance of the quantum dot is improved. Thus, SnO₂The quantum dot/graphene composite can be used as one of ideal materials of a lithium ion battery cathode. At present, various methods for preparing SnO have been reported₂A method of quantum dot/graphene composite. As disclosed in CN107055516A, the SnO obtained by microwave hydrothermal reaction for 5-120 min at 120-180 deg.C₂The tin dioxide quantum dots in the quantum dot/graphene composite are uniform in size and are uniformly distributed on two sides of the graphene sheet; CN105895874A discloses that SnO is obtained by multiple ball milling, pretreatment, high-temperature calcination and suction filtration₂A quantum dot/graphene composite; CN103441254A discloses that SnO is prepared by adopting urea as a reducing agent, refluxing for 16 hours at 85-90 ℃, calcining for 2 hours at high temperature and reducing graphite oxide₂A quantum dot/graphene composite. Although these methods may improve SnO to varying degrees₂The deposition effect of the quantum dots on the graphene still cannot reach an ultra-uniform dispersion state. In another aspect, SnO_xSpecific SnO is obtained due to the abundance of oxygen vacancies on the surface₂Higher capacity, additional pseudocapacitance effects may be added due to oxygen vacancies. However, SnO has been reported at present_xPreparation of quantum dots and SnO₂Quantum dots face the same problem.

The excimer ultraviolet irradiation technology has the characteristics of simplicity, energy conservation, greenness, high efficiency and the like, and the operation condition is controllable, so that the excimer ultraviolet irradiation technology is extremely suitable for large-area processing and is widely applied to the fields of health care, food processing and the like. Excimer ultraviolet irradiation is used for surface treatment of carbon nanofiber membranes and has been reported as a lithium ion battery cathode material, but the excimer ultraviolet irradiation is used as an auxiliary deposition technology and is applied to SnO_xThe preparation method of the quantum dot/graphene composite is not reported.

Disclosure of Invention

The invention provides simple, convenient and efficient SnO applied to a lithium ion battery cathode_xA preparation method of a quantum dot/graphene composite.

The technical scheme adopted by the invention for solving the technical problems is as follows:

carbon-coated SnO applied to lithium ion battery cathode_xA preparation method of a quantum dot/graphene composite comprises the following steps:

(1) preparation of a solution to be irradiated: a. mixing graphene with deionized water, and ultrasonically mixing uniformly; b. fully dissolving sucrose in dilute hydrochloric acid, and adding stannous chloride; c. mixing and stirring the two mixed solutions obtained in the step a and the step b uniformly to obtain a solution to be irradiated; the mass fraction of graphene in the solution to be irradiated is 0.08-0.4%, the mass fraction of sucrose is 2-15%, the mass fraction of stannous chloride is 5-20%, and the concentration of dilute hydrochloric acid is 1-3%;

(2) irradiation: placing the solution to be irradiated obtained in the step (1) under an excimer light source for irradiation, and stirring simultaneously;

(3) carbon coated SnO_xPreparing a quantum dot/graphene composite: subjecting the product obtained in step (2) to reaction in H₂Calcining in the atmosphere of/Ar mixed gas to prepare the carbon-coated SnO_xA quantum dot/graphene composite.

The preparation method is simple, short in flow and high in efficiency. SnO_xThe quantum dots can provide high lithium storage capacity; the carbon coating layer not only effectively disperses SnO_xQuantum dots, and can be used as SnO_xThe volume change generated in the charging and discharging process plays a role in inhibiting, and electrons can be accelerated in SnO_xMigration of the quantum dot surface layer. Such carbon-coated SnO_xThe quantum dot/graphene composite can be used as a negative electrode material of a lithium ion battery and a sodium ion battery.

Preferably, in the step (1), the mixing and stirring time is 2-10 min.

Preferably, in the step (1), the mass fraction of graphene in the solution to be irradiated is 0.15-0.35%, the mass fraction of sucrose is 5-12%, the mass fraction of stannous chloride is 5-15%, and the concentration of dilute hydrochloric acid is 1.5-2%. Mixing and stirring for 4-7 min.

The content of graphene is too low, so that uneven deposition is easily caused, and the graphene is not easily subjected to ultrasonic dispersion when the content of graphene is too high; too low a sucrose content, insignificant coating effect, too high a decrease in the final SnO_xThe relative content of the quantum dots, so that the specific capacity of the negative electrode is reduced; the content of the stannous chloride is too low,insufficient deposition can be caused, so that the specific capacity of the cathode is reduced, and uneven deposition can be caused if the specific capacity is too high; the dilute hydrochloric acid plays a role in protecting stannous chloride from being oxidized, the process effect is not obvious, and meanwhile, the dilute hydrochloric acid can dissolve part of formed SnO_xQuantum dots, therefore, too high a content reduces SnO_xThe relative content of the quantum dots, thereby reducing the specific capacity of the negative electrode.

Preferably, the excimer light source is KrCl^*、XeCl^*Or Xe₂ ^*KrCl is the most preferred.

XeCl^*The wavelength of the excimer ultraviolet lamp is 308nm, and the excimer ultraviolet lamp is used as an auxiliary deposition light source, so that the provided energy is not high enough, and the efficiency is low; xe (Xe)₂ ^*The wavelength of the molecular ultraviolet lamp is 172nm, under the illumination of the wavelength, oxygen in the air can be converted into ozone, and the excessive oxygen is harmful to human bodies, so that the requirement on the irradiation environment is high; KrCl^*The wavelength of the excimer ultraviolet lamp is 222nm, the excimer ultraviolet lamp is relatively mild and efficient, the excimer ultraviolet lamp is suitable for being applied in an open environment, and the requirements on the surrounding environment and auxiliary equipment are low.

Preferably, in the step (2), the irradiation distance is 0.2-1cm, the irradiation time is 1-60min, and the stirring speed is 50-200 r/min. Further, in the step (2), the irradiation distance is 0.3-0.7cm, the irradiation time is 10-40min, and the stirring speed is 10-150 r/min. The distance is too short, the control is not easy, and the effect is not good when the distance is too long; too short a time and low efficiency, and too long a time causes damage to equipment; the stirring is too slow, which easily causes the graphene to precipitate and causes SnO_xThe quantum dots are deposited unevenly, and too fast, the irradiation is insufficient, and the deposition quality is influenced.

Preferably, in the step (3), H₂The flow rate of the/Ar mixed gas is 50-500sccm, the calcination temperature is 300-500 ℃, and the time is 0.5-3 h. The flow, the calcination temperature and the time value are too small, the effect is not obvious, if the flow, the calcination temperature and the time value are too large, simple substance tin is easy to form, and large particles are formed by melting and agglomerating at 400 ℃.

The invention relates to carbon-coated SnO applied to a lithium ion battery cathode_xThe preparation method of the quantum dot/graphene compound comprises the steps of firstly preparing dispersion liquid of graphene and deionized water, sucrose, stannous chloride, and the like,A solution of dilute hydrochloric acid; after being mixed evenly, the mixture is irradiated by excimer ultraviolet light; then the carbon-coated SnO is obtained by high-temperature calcination_xA quantum dot/graphene composite. The carbon-coated SnO prepared by the method_xThe quantum dot/graphene composite can be used in the field of lithium ion battery energy storage. The preparation method has the following characteristics:

(1) the preparation method is simple and convenient, short in flow, high in efficiency, and easy to realize and control the irradiation condition.

(2) The prepared carbon coating layer is uniformly covered on SnO_xOn the quantum dots, SnO can be inhibited_xThe volume effect of the quantum dots in the electrochemical process can also be SnO_xThe quantum dots provide a fast electron transmission channel, thereby improving SnO_xThe quantum dot/graphene composite negative electrode has the cycling stability and rate capability.

(3) Prepared SnO_xThe quantum dots are separated by the carbon coating layer and are deposited on the graphene in a highly dispersed manner, so that each SnO is reinforced_xThe quantum dots are contacted with the graphene, so that efficient electrochemical reaction conditions are provided, and carbon-coated SnO is enhanced_xRate capability of the quantum dot/graphene composite negative electrode.

(4) Prepared SnO_xThe quantum dots contain rich oxygen holes, so the quantum dots have pseudocapacitance effect and can greatly improve the carbon-coated SnO_xThe rate capability of the quantum dot/graphene composite negative electrode.

Drawings

FIG. 1 is a carbon-coated SnO prepared in example 1_xTEM transmission electron microscope images of the quantum dot/graphene composite.

FIG. 2 is a carbon-coated SnO prepared in example 1_xA high-resolution TEM transmission electron microscope image of the quantum dot/graphene composite.

FIG. 3 is SnO prepared in example 2_xTEM transmission electron microscope images of the quantum dot/graphene composite.

FIG. 4 is a carbon-coated SnO prepared in example 3_xTEM transmission electron microscope images of the quantum dot/graphene composite.

FIG. 5 is carbon-coated SnO prepared in example 4_xQuantum dot/graphene composite TEM transmissionElectron emission microscopy.

FIG. 6 is carbon-coated SnO prepared in example 5_xTEM transmission electron microscope images of the quantum dot/graphene composite.

FIG. 7 is SnO prepared in example 6₂A high-resolution TEM transmission electron microscope image of the quantum dot/graphene composite.

FIG. 8 is a carbon-coated SnO prepared in example 1_xQuantum dot/graphene composite and carbon-coated SnO prepared in example 6₂ESR electron spin resonance spectrogram of the quantum dot/graphene compound.

FIG. 9 is carbon-coated SnO prepared in example 1_xQuantum dot/graphene composite, example 6 carbon-coated SnO₂A rate performance graph of the quantum dot/graphene composite.

Detailed Description

The technical solution of the present invention will be further specifically described below by way of specific examples. It is to be understood that the practice of the invention is not limited to the following examples, and that any variations and/or modifications may be made thereto without departing from the scope of the invention.

In the invention, all parts and percentages are weight units, and all equipment, raw materials and the like can be purchased from the market or are commonly used in the industry, if not specified.

Example 1

Carbon-coated SnO applied to lithium ion battery cathode_xThe preparation method of the quantum dot/graphene composite comprises the following steps:

(1) accurately weighing 60mg of graphene powder by using an analytical balance, and ultrasonically dispersing the graphene powder in 10mL of deionized water; and weighing 2g of sucrose, dissolving the sucrose in 10mL of 1.8% diluted hydrochloric acid, adding 1.6g of stannous chloride dihydrate powder, fully dissolving, and mixing and stirring the mixture with the graphene water dispersion for 5 minutes to obtain a uniform and stable solution to be irradiated.

(2) Irradiation: placing the solution to be irradiated in KrCl^*Stirring and irradiating at a position of 0.5cm below the excimer light source for 20min at a stirring speed of 50 r/min.

(3) After the irradiated mixed liquid is cleaned and dried, theH₂Calcining in the atmosphere of/Ar mixed gas, and controlling H₂The flow rate of the/Ar mixed gas is 50sccm, the calcining temperature is 400 ℃, and the time is 1h, so that the carbon-coated SnO is prepared_xA quantum dot/graphene composite.

Example 2

(1) accurately weighing 60mg of graphene powder by using an analytical balance, and ultrasonically dispersing the graphene powder in 10mL of deionized water; separately, 1.6g of stannous chloride dihydrate powder was weighed, dissolved in 10mL of 1.8% diluted hydrochloric acid, and mixed with the aqueous dispersion of graphene and stirred for 5 minutes.

(3) Washing and drying the irradiated mixture, and reacting with hydrogen peroxide in the presence of hydrogen peroxide₂Calcining in the atmosphere of/Ar mixed gas, and controlling H₂The flow rate of the/Ar mixed gas is 50sccm, the calcining temperature is 400 ℃, and the time is 1h, so that the carbon-coated SnO is prepared_xA quantum dot/graphene composite.

Example 3

(2) And (3) stirring the mixed solution in the step (1) for 20min at a stirring speed of 50 revolutions per minute.

(3) Washing and drying the mixed solution obtained in the step (2), and adding the washed and dried mixed solution to H₂Calcining in the atmosphere of/Ar mixed gas, and controlling H₂The flow rate of the/Ar mixed gas is 50sccm, the calcining temperature is 400 ℃, and the time is 1h, so that the carbon-coated SnO is prepared_xA quantum dot/graphene composite.

Example 4

(2) Irradiation: placing the solution to be irradiated in KrCl^*Stirring and irradiating at a position of 0.5cm below the excimer light source for 10min at a stirring speed of 50 r/min.

Example 5

(2) Irradiation: placing the solution to be irradiated in KrCl^*Stirring and irradiating at a position of 0.5cm below the excimer light source for 30min at a stirring speed of 50 r/min.

Example 6

(3) Cleaning and drying the irradiated mixed solution, calcining in an Ar mixed gas atmosphere, controlling the flow of the Ar mixed gas to be 50sccm, the calcining temperature to be 400 ℃ and the calcining time to be 1h, and preparing the carbon-coated SnO₂A quantum dot/graphene composite.

Three comparative examples of variables were made for this group: 1. adding sucrose or not (examples 1 and 2); 2.

irradiation times

0, 10, 20, 30min (examples 3, 4, 1, 5); 3. introducing H during calcination₂The following conclusions were obtained from the experimental results analysis for/Ar and pure Ar (examples 1, 6):

as observed by TEM transmission electron microscopy of fig. 1 and 3, example 1: adding sucrose into the raw materials to obtain carbon-coated SnO_xIn the quantum dot/graphene composite, SnO is coated by carbon_xThe dispersibility of the quantum dots on the graphene is obviously better than that of SnO added without cane sugar_xA quantum dot/graphene composite.

According to TEM observation of figures 1, 4, 5 and 6, the carbon-coated SnO can be observed along with the prolonging of the irradiation time_xThe deposition of quantum dots on graphene is gradually increased; when the irradiation time is 20min and 30min, the carbon is coated with SnO_xThe deposition amount of the quantum dots is not obviously changed, which shows that when the irradiation time is 20min, the carbon is coated with SnO_xThe quantum dots achieve the optimal deposition amount on the graphene.

By observation of the high resolution TEM in FIGS. 2 and 7, it was found that₂Mixed atmosphere of/ArCalcining at high temperature to obtain carbon-coated SnO_xQuantum dots, and in pure Ar atmosphere, carbon-coated SnO is obtained₂And (4) quantum dots.

As can be seen from the electron paramagnetic resonance spectroscopy analysis of fig. 8, in H₂SnO obtained by calcining in/Ar mixed atmosphere_xThe quantum dots have oxygen vacancies, further proving that SnO is coated by carbon_xThe presence of quantum dots.

Here, SnO is coated with carbon_xDescription of basic properties of quantum dot/graphene composite, comparison of properties of the same kind of product is described below.

The carbon-coated SnO obtained in example 1_xThe quantum dot/graphene composite is used as a lithium ion battery cathode to perform electrochemical tests, and the rate performance graph of the lithium ion battery cathode is shown in fig. 9. As can be seen from FIG. 9, carbon-coated SnO_xQuantum dot/graphene composite cathode battery and carbon-coated SnO₂The initial discharge capacities of the quantum dot/graphene composite negative electrode batteries are almost consistent; when the current density is gradually increased from 0.05A/g to 3.2A/g, the carbon-coated SnO_xThe quantum dot/graphene composite negative electrode battery shows obvious capacity advantage; carbon coated SnO when the current density returns to 0.05A/g again_xThe quantum dot/graphene composite negative electrode battery has high capacity. The test results show that the carbon-coated SnO prepared in example 1_xThe quantum dot/graphene composite negative electrode battery shows the best rate performance.

The above-described embodiments are only preferred embodiments of the present invention, and are not intended to limit the present invention in any way, and other variations and modifications may be made without departing from the spirit of the invention as set forth in the claims.

Claims

1. Carbon-coated SnO applied to lithium ion battery cathode_xThe preparation method of the quantum dot/graphene composite is characterized by comprising the following steps:

the excimer light source is KrCl^*；

KrCl^*The wavelength of the excimer ultraviolet lamp is 222nm, the irradiation distance is 0.3-0.7cm, the irradiation time is 10-40min, and the stirring speed is 10-150 r/min;

(3) carbon coated SnO_xPreparing a quantum dot/graphene composite: subjecting the product obtained in step (2) to reaction in H₂Calcining in the atmosphere of/Ar mixed gas to prepare the carbon-coated SnO_xA quantum dot/graphene composite;

H₂the flow rate of the/Ar mixed gas is 50-500sccm, the calcination temperature is 300-500 ℃, and the time is 0.5-3 h.

2. The method of claim 1, wherein: in the step (1), the mixing and stirring time is 2-10 min.

3. The method of claim 1, wherein: in the step (1), the mass fraction of graphene in the solution to be irradiated is 0.15-0.35%, the mass fraction of sucrose is 5-12%, the mass fraction of stannous chloride is 5-15%, and the concentration of dilute hydrochloric acid is 1.5-2%.