WO2017139983A1

WO2017139983A1 - Method for preparing positive electrode material having three-dimensional nitrogen-doped structure for use in lithium-sulfur battery

Info

Publication number: WO2017139983A1
Application number: PCT/CN2016/074172
Authority: WO
Inventors: 肖丽芳; 钟玲珑
Original assignee: 肖丽芳
Priority date: 2016-02-19
Filing date: 2016-02-19
Publication date: 2017-08-24

Abstract

Provided in the present invention is a method for preparing a positive electrode material having a three-dimensional nitrogen-doped structure for use in a lithium-sulfur battery, which comprises the following steps: (1) adding graphite oxide into water to perform ultrasonic treatment, so as to form a graphene oxide suspension; (2) adding ammonia water to the graphene oxide suspension to obtain a three-dimensional nitrogen-doped graphene; (3) adding the three-dimensional nitrogen-doped graphene obtained from step (2) and ketjen black into N-methyl pyrrolidone to conduct an ultrasonic treatment so as to form a suspension; (4) adding ammonia water to the graphene oxide suspension, and adding elemental sulfur to N-methyl pyrrolidone to perform an ultrasonic reaction until the elemental sulfur is fully dissolved to form a suspension; (5) mixing the two suspensions obtained from step (4) and step (3), stirring uniformly, and slowly adding distilled water while stirring to obtain the positive electrode material having a three-dimensional structure for use in a lithium-sulfur battery. The sulfur adsorption effect of nitrogen atoms in the nitrogen-doped graphene can effectively reduce the shuttle effect, and thus extending the cycle life of a lithium-sulfur battery.

Description

Method for preparing cathode material of three-dimensional nitrogen-doped structure lithium-sulfur battery

Technical field

The invention relates to the synthesis of nano materials, in particular to a preparation method of a cathode material for a lithium sulfur battery.

Background technique

The lithium-sulfur battery is a battery system in which lithium metal is used as a negative electrode and elemental sulfur is used as a positive electrode. Lithium-sulfur batteries have two discharge platforms (about 2.4V and 2.1V), but their electrochemical reaction mechanism is complicated. Lithium-sulfur batteries have the advantages of high specific energy (2600Wh/kg), high specific capacity (1675mAh/g), low cost, etc., and are considered to be promising new generation batteries. However, at present, there are problems such as low utilization rate of active materials, low cycle life and poor safety, which seriously restricts the development of lithium-sulfur batteries. The main causes of the above problems are as follows: (1) Elemental sulfur is an electron and ionic insulator, and the room temperature conductivity is low (5 × 10 ^{-30 S} · cm ^-1 ). Since there is no ionic sulfur, it acts as a positive electrode. activation difficult material; (2) generated in the electrode reaction during the high polymer state lithium polysulfides _{_{Li 2 S n (8> n≥4}} ) soluble, is formed between the positive and negative electrodes in the electrolyte concentration difference, the concentration The gradient migrates to the negative electrode, and the high poly lithium polysulfide is reduced by the lithium metal to the oligomeric lithium polysulfide. As the above reaction proceeds, the oligomeric lithium polysulfide aggregates at the negative electrode, eventually forming a concentration difference between the two electrodes, and then migrating to the positive electrode to be oxidized to a highly polylithium polysulfide. This phenomenon is known as the shuttle effect, which reduces the utilization of sulfur active substances. At the same time, insoluble Li ₂ S and Li ₂ S _{2 are} deposited on the surface of the lithium negative electrode, which further deteriorates the performance of the lithium-sulfur battery; (3) the final product of the reaction, Li ₂ S, is also an electronic insulator, which is deposited on the sulfur electrode, and lithium slow ion mobility in the solid state lithium sulfide, the slow electrochemical reaction kinetics; different density (4) sulfur and Li ₂ S final product when sulfur is expanded to about 79% of the volume of lithium, Li ₂ easily lead The powdering of S causes safety problems in lithium-sulfur batteries. The above-mentioned shortcomings restrict the development of lithium-sulfur batteries, which is also the key issue that needs to be solved in the research of lithium-sulfur batteries.

technical problem

The technical problem to be solved by the present invention is to provide a three-dimensional structure lithium-sulfur battery cathode material, and the three-dimensional structure of nitrogen-doped graphene, nano-sulfur particles and Ketjen black deposited on nitrogen-doped graphene are prepared by the method. In this design, the conductivity of the sulfur motor can be improved and the dissolution of the polysulfide of the discharge product can be prevented.

Problem solution

Technical solution

The invention provides a preparation process of a three-dimensional lithium-sulfur battery cathode material as follows:

(1) adding graphite oxide to water to form a graphene oxide suspension;

(2) Ammonia water with a mass concentration of 25% is added to the graphene oxide suspension, and then transferred to a hydrothermal kettle for hydrothermal reaction. After the reaction is completed, the ethanol is washed, washed with water, and then freeze-dried to obtain a three-dimensional nitrogen-doped graphite. Alkene

(3) taking the three-dimensional nitrogen-doped graphene obtained in the step (2) and adding Ketjen black to N-methylpyrrolidone to form a suspension;

(4) adding elemental sulfur to N-methylpyrrolidone and sonicating at a certain temperature until the elemental sulfur is completely dissolved to form a suspension;

(5) Mixing the two suspensions obtained in (4) and (3), stirring uniformly, and then slowly adding distilled water under stirring, centrifuging, washing with water, and drying to obtain a three-dimensional lithium-sulfur battery cathode material.

The ultrasonic reaction time in the step (1) is 10-60 minutes, and the concentration of the graphene oxide suspension is 1-10 g/L;

The temperature of the hydrothermal reaction in the step (2) is 160-200 ° C, the reaction time is 1-6 hours, and the ratio of graphite oxide to ammonia water is 1 g: 10-50 mL;

The mass ratio of the three-dimensional nitrogen-doped graphene to the Ketjen black in the step (3) is 1:0.05-0.5, and the concentration of the suspension is 1-5 g/L;

In step (4), the mass ratio of elemental sulfur to three-dimensional nitrogen-doped graphene and Ketjen black is 10-20:1, the reaction temperature of ultrasonic is 40-50 ° C, and the ultrasonic time is until sulfur is completely dissolved, and sulfur suspension The concentration of the liquid is 10-15 g / L;

Distilled water added in the step (5): The volume ratio of the N-methylpyrrolidone solution after mixing is 3-5:1.

Advantageous effects of the invention

Beneficial effect

The invention has the following beneficial effects: (1) the preparation method reduces the graphite oxide, nitrogen doping and hydrothermal reaction in one step, and improves the reaction efficiency; (2) the high conductivity Ketchen black and graphene materials can effectively improve the electrode The conductivity of the sheet; (3) during the charging and discharging process, the structure of the three-dimensional structure facilitates the shuttle of lithium ions and electrons in the multi-dimensional conduction path, and improves the ion and electron conductivity; (4) the existence of the three-dimensional structure Keqin black further shortens the conduction distance between nano-sulfur particles and nano-sulfur and graphene sheets, which is beneficial to the improvement of electrical conductivity; (5) the adsorption of sulfur by nitrogen atoms in nitrogen-doped graphene is effective Reduce the shuttle effect and increase the cycle life of lithium-sulfur batteries.

Brief description of the drawing

DRAWINGS

1 is an SEM image of a three-dimensional nitrogen-doped graphene sulfur composite prepared by the present invention.

Invention embodiment

Embodiments of the invention

The preferred embodiments of the present invention are further described in detail below with reference to the accompanying drawings:

Example 1

(1) 10 mg of graphite oxide was added to 10 mL of water for 10 minutes to form a 1 g/L graphene oxide suspension;

(2) Add 100 mL of 25% ammonia water to the graphene oxide suspension, then transfer to a hydrothermal kettle for reaction, and react at 160 ° C for 6 hours. After the reaction is completed, wash with ethanol, wash with water, and then freeze-dry to obtain three-dimensional. Nitrogen doped graphene;

(3) taking 10 mg of the three-dimensional nitrogen-doped graphene obtained in (2) and adding 5 mg of Ketjen black to 15 mL of N-methylpyrrolidone to form a 1 g/L suspension;

(4) 150 mg of elemental sulfur was added to 15 mL of N-methylpyrrolidone at a certain temperature of 40 ° C until the elemental sulfur was completely dissolved to form a 10 g / L suspension;

(5) Mixing the two suspensions obtained in (4) and (3), stirring uniformly, and then slowly adding 90 mL of distilled water under stirring, centrifuging, washing with water, and drying to obtain a lithium-sulfur battery positive electrode material having a three-dimensional structure.

Example 2

(1) 10 mg of graphite oxide was added to 1 mL of water for 60 minutes to form a 10 g/L graphene oxide suspension;

(2) Add 500 mL of 25% ammonia water to the graphene oxide suspension, then transfer to a hydrothermal kettle for reaction, and react at 200 ° C for 1 hour. After the reaction is completed, wash with ethanol, wash with water, and then freeze-dry to obtain three-dimensional. Nitrogen doped graphene;

(3) taking 10 mg of the three-dimensional nitrogen-doped graphene obtained in (2) and adding 0.5 mg of Ketjen black to 2.1 mL of N-methylpyrrolidone to form a 5 g/L suspension;

(4) 210 mg of elemental sulfur was added to 14 mL of N-methylpyrrolidone at 50 ° C until the elemental sulfur was completely dissolved to form a 15 g / L suspension;

(5) Mixing the two suspensions obtained in (4) and (3), stirring uniformly, and then slowly adding 80.5 mL of distilled water under stirring, centrifuging, washing with water, and drying to obtain a lithium-sulfur battery cathode material having a three-dimensional structure.

Example 3

(1) 10 mg of graphite oxide was added to 5 mL of water for 30 minutes to form a 2 g/L graphene oxide suspension;

(2) 200 mL of 25% ammonia water is added to the graphene oxide suspension, and then transferred to a hydrothermal kettle for reaction, and reacted at 180 ° C for 3 hours. After the reaction is completed, the ethanol is washed, washed with water, and then freeze-dried to obtain a three-dimensional shape. Nitrogen doped graphene;

(3) taking 10 mg of the three-dimensional nitrogen-doped graphene obtained in (2) and adding 1 mg of Ketjen black to 5.5 mL of N-methylpyrrolidone to form a 2 g/L suspension;

(4) 132 mg of elemental sulfur was added to 11 mL of N-methylpyrrolidone at 45 ° C until the elemental sulfur was completely dissolved to form a 12 g / L suspension;

(5) Mixing the two suspensions obtained in (4) and (3), stirring uniformly, and then slowly adding 66 mL of distilled water under stirring, centrifuging, washing with water, and drying to obtain a lithium-sulfur battery positive electrode material having a three-dimensional structure.

Example 4

(1) 10 mg of graphite oxide was added to 2 mL of water for 20 minutes to form a 5 g/L graphene oxide suspension;

(2) Add 300mL of ammonia water with a concentration of 25% to the graphene oxide suspension, then transfer to a hydrothermal kettle for reaction, and react at 170 ° C for 5 hours. After the reaction is completed, wash with ethanol, wash with water, and then freeze-dry to obtain three-dimensional. Nitrogen doped graphene;

(3) Take 10 mg of three-dimensional nitrogen-doped graphene obtained with (2) and add 2 mg of Ketjen black to 4 mL of N-methyl group. Ultrasonic formation of a 3 g/L suspension in pyrrolidone;

(4) 156 mg of elemental sulfur was added to 12 mL of N-methylpyrrolidone and sonicated at 42 ° C until the elemental sulfur was completely dissolved to form a 13 g / L suspension;

(5) Mixing the two suspensions obtained in (4) and (3), stirring uniformly, and then slowly adding 72 mL of distilled water under stirring, centrifuging, washing with water, and drying to obtain a lithium-sulfur battery cathode material having a three-dimensional structure.

Example 5

(1) 10 mg of graphite oxide was added to 4 mL of water for 40 minutes to form a 2.5 g/L graphene oxide suspension;

(2) 400 mL of 25% ammonia water is added to the graphene oxide suspension, and then transferred to a hydrothermal kettle for reaction, and reacted at 190 ° C for 2 hours. After the reaction is completed, the mixture is washed with ethanol, washed with water, and then freeze-dried to obtain a three-dimensional shape. Nitrogen doped graphene;

(3) taking 10 mg of the three-dimensional nitrogen-doped graphene obtained in (2) and adding 3 mg of Ketjen black to 3.25 mL of N-methylpyrrolidone to form a 4 g/L suspension;

(4) 182 mg of elemental sulfur was added to 13 mL of N-methylpyrrolidone and sonicated at 48 ° C until the elemental sulfur was completely dissolved to form a suspension of 14 g / L;

(5) Mixing the two suspensions obtained in (4) and (3), stirring uniformly, and then slowly adding 56.875 mL of distilled water under stirring, centrifuging, washing with water, and drying to obtain a lithium-sulfur battery cathode material having a three-dimensional structure.

Electrode preparation and performance test; electrode material, acetylene black and PVDF were mixed in NMP at a mass ratio of 80:10:10, coated on aluminum foil as electrode film, lithium metal plate as counter electrode, CELGARD 2400 as separator, 1 mol /L LiTFSI/DOL-DME (volume ratio 1:1) is an electrolyte, 1 mol/L LiNO ₃ is an additive, assembled into a button-type battery in a filled glove box, and a constant current charge and discharge is performed using a Land battery test system. test. The charge and discharge voltage range is 1-3V, the current density is 0.01C, and the performance is shown in Table 1.

Table 1

[Table 1]

1 is an SEM image of a positive electrode material prepared by the present invention. It can be seen from the figure that the positive electrode material has a large number of open three-dimensional pore-like structures, which can provide an ion transport channel and improve the electrochemical performance of the material.

The above is a further detailed description of the present invention in connection with the specific preferred embodiments, and the specific embodiments of the present invention are not limited to the description. It will be apparent to those skilled in the art that the present invention may be made without departing from the spirit and scope of the invention.

Claims

A method for preparing a three-dimensional nitrogen-doped lithium-sulfur battery cathode material, comprising the following steps:

Step (1): adding graphite oxide to water to form a graphene oxide suspension;

Step (2): adding ammonia water to the graphene oxide suspension, and then transferring to a hydrothermal kettle for hydrothermal reaction, after the reaction is completed, washing with ethanol, washing with water, and then lyophilizing to obtain three-dimensional nitrogen-doped graphene;

Step (3): taking the three-dimensional nitrogen-doped graphene obtained in the step (2) and adding Ketjen black to N-methylpyrrolidone to form a suspension by ultrasonic reaction;

Step (4): adding ammonia water to the graphene oxide suspension step (4) adding elemental sulfur to the N-methylpyrrolidone for ultrasonication until the elemental sulfur is completely dissolved to form a suspension;

Step (5): mixing the two suspensions obtained in the step (4) and the step (3), stirring uniformly, and then slowly adding distilled water under stirring, centrifuging, washing with water, and drying to obtain a three-dimensional lithium-sulfur battery cathode material. .
The preparation method according to claim 1, wherein the ultrasonic reaction time in the step (1) is from 10 to 60 minutes, and the concentration of the graphene oxide suspension is from 1 to 10 g/L.
The production method according to claim 1, wherein the mass concentration of the aqueous ammonia in the steps (2) and (4) is 25%.
The preparation method according to claim 1, wherein the temperature of the hydrothermal reaction in the step (2) is 160-200 ° C, the reaction time is 1-6 hours, and the ratio of graphite oxide to ammonia water is 1 g: 10 -50 mL.
The preparation method according to claim 1, wherein the mass ratio of the three-dimensional nitrogen-doped graphene to the Ketjen black in the step (3) is 1:0.05-0.5, and the concentration of the suspension is 1-5 g/ L.
The preparation method according to claim 1, wherein the mass ratio of the elemental sulfur to the three-dimensional nitrogen-doped graphene and the ketjen black in the step (4) is 10-20:1, The ultrasonic reaction temperature is 40-50 ° C, and the ultrasonic time is until the sulfur is completely dissolved, and the concentration of the sulfur suspension is 10-15 g/L.
The preparation method according to claim 1, wherein the volume ratio of the distilled water added in the step (5) to the mixed N-methylpyrrolidone solution is 3-5:1.