WO2017139993A1

WO2017139993A1 - Method for preparing doped lithium sulfide composite coated with graphene/carbon and having core-shell structure

Info

Publication number: WO2017139993A1
Application number: PCT/CN2016/074192
Authority: WO
Inventors: 肖丽芳; 钟玲珑
Original assignee: 肖丽芳
Priority date: 2016-02-21
Filing date: 2016-02-21
Publication date: 2017-08-24

Abstract

A method for preparing doped lithium sulfide composite coated with graphene/carbon and having a core-shell structure, comprises: step (1), mixing commercial lithium sulfide with metal oxide powder, sealing the mixture into a ball milling tank, puting the tank into a ball mill to perform milling to obtain doped nano lithium sulfide; step (2), adding and dissolving a carbon source into ethanol under stirring so as to form an ethanol solution containing the carbon source; step (3), dispersing the obtained nano lithium sulfide in an ethanol solution, and adding dropwisely the ethanol solution containing the carbon source into the suspension to obtain a lithium sulfide coated with carbon; step (4) adding the lithium sulfide coated with carbon and graphene to tetrahydrofuran and performing a ultrasonic reaction so as to obtain the doped lithium sulfide composite coated with graphene/carbon and having a core-shell structure. Doping metal ions can change the crystal structure of lithium sulfide, and is beneficial to improve the bulk conductivity of lithium sulfide and the electrochemical performance thereof.

Description

Preparation method of graphene/carbon coated doped lithium sulfide composite material with core-shell structure

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 ion insulator, and the room temperature conductivity is low (5 × 10 ^-30 S·cm ^-1 ). Since there is no ionic sulfur, it is used as The activation of the positive electrode material is difficult; (2) the high polylithium polysulfide Li ₂ S _n (8>n≥4) generated during the electrode reaction is easily dissolved in the electrolyte, forming a concentration difference between the positive and negative electrodes. Under the action of the concentration gradient, it 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.

In the lithium-sulfur battery system, since the sulfur-based positive electrode does not contain lithium, lithium metal is required as the negative electrode to provide the lithium source. However, during the recycling process, the lithium metal negative electrode is liable to form lithium dendrite and powder on the surface, which not only has safety hazards. Moreover, the consumption of the electrolyte leads to the premature failure of the lithium-sulfur secondary battery, which limits the application of the lithium-sulfur battery. Researchers use Li ₂ S instead of sulfur-based positive electrode, or pre-lithiated sulfur-based positive electrode, using carbon negative electrode or silicon and tin with higher capacity as negative electrode material, in order to eliminate the influence of lithium metal negative electrode, lithium sulfide positive electrode The theoretical capacity is high, 1166 mAh / g, but it is also an insulating material like the sulfur electrode, it needs to add conductive additives, and special coating treatment to improve its electrochemical activity.

technical problem

The technical problem to be solved by the present invention is to provide a method for preparing a graphene/carbon coated doped lithium sulfide composite material having a core-shell structure, the preparation method is simple, and the conductive conductive graphene and the carbon shell provide a conductive network, and at the same time The doped metal ions change the lattice structure of lithium sulfide, improve its conductivity, and further improve its electrochemical activity.

Problem solution

Technical solution

The invention provides a preparation method of graphene/carbon coated doped lithium sulfide composite material with core-shell structure:

(1) Commercial lithium sulfide is mixed with metal oxide powder in an inert gas-protected glove box, and then placed in a sealed ball-milling tank, and then placed in a ball mill for ball milling to obtain doped nano-lithium sulfide.

(2) A carbon source is added to ethanol under stirring to dissolve to form an ethanol solution containing a carbon source.

(3) Dispersing the obtained nano lithium sulfide into an ethanol solution, continuously stirring to form a suspension, and then adding an ethanol solution containing a carbon source to the suspension, stirring the reaction at room temperature, then evaporating the solvent, and adding to the inert gas protection The muffle furnace reacts at a high temperature to obtain carbon-coated lithium sulfide.

(4) Carbon-coated lithium sulfide and graphene are added to tetrahydrofuran, ultrasonically reacted, and then the solvent is evaporated to obtain a graphene/carbon coated doped lithium sulfide composite.

The mass ratio of lithium sulfide to metal oxide in the step (1) is 100:0.5-5; the metal oxide may be one or more of magnesium oxide, manganese dioxide, copper oxide, aluminum oxide and nickel oxide; The time is 0.5-3 hours and the ball milling speed is 500-3000 rpm.

The organic carbon source in the step (2) is one or more of sucrose, glucose, starch, cellulose; and the mass concentration of the forming solution is 5-10%.

Step (3) The lithium sulfide ethanol solution has a mass concentration of 5-10%; the volume ratio of the carbon source ethanol solution to the lithium sulfide ethanol solution is 1:1-10; the room temperature stirring reaction time is 1-5 hours, in the muffle furnace Reaction temperature It is 800-900 ° C; the reaction time is 1-5 hours.

The mass ratio of graphene to carbon-coated lithium sulfide in step (4) is 1:10-100; the ultrasonic time is 0.5-3 hours.

Advantageous effects of the invention

Beneficial effect

The invention has the following beneficial effects: (1) both graphene and carbon have ultra-high electrical conductivity, graphene and carbon coating on the surface of lithium sulfide can effectively improve the electrical conductivity of the material; (2) doping metal ions can change The crystal structure of lithium sulfide is beneficial to the improvement of the bulk conductivity of lithium sulfide and the improvement of its electrochemical performance.

Brief description of the drawing

DRAWINGS

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is an SEM image of a graphene/carbon coated doped lithium sulfide composite prepared in accordance with 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) 100 mg of commercial lithium sulfide and 5 mg of magnesium oxide powder were mixed in an inert gas-protected glove box, and then placed in a sealed ball-milling jar, and then ball-milled for 0.5 hour at a ball milling speed of 3,000 rpm. Nano lithium sulfide.

(2) The sucrose was added to ethanol under stirring to dissolve to form a sucrose ethanol solution having a mass concentration of 10%.

(3) Dispersing the obtained nano lithium sulfide into an ethanol solution, stirring continuously to form a 50 ml suspension having a mass concentration of 10%, and then dropping 50 ml of the sucrose ethanol solution into the suspension, stirring the reaction at room temperature for 5 hours, and then evaporating. The solvent was added to an inert gas-protected muffle furnace at 800 ° C for 5 hours to obtain carbon-coated lithium sulfide.

(4) 100 mg of carbon-coated lithium sulfide and 10 mg of graphene were added to tetrahydrofuran, and ultrasonically reacted for 0.5 hour, and then the solvent was evaporated to obtain a graphene/carbon coated doped lithium sulfide composite.

Example 2

(1) 100 mg of commercial lithium sulfide and 0.5 mg of manganese dioxide powder were mixed in an inert gas-protected glove box, and then placed in a sealed ball mill jar, and then ball milled for 3 hours at a ball milling speed of 500 rpm. , obtained nano lithium sulfide.

(2) Glucose was added to ethanol under stirring to dissolve to form a glucose ethanol solution having a mass concentration of 5%.

(3) Dispersing the obtained nano lithium sulfide into an ethanol solution, continuously stirring to form a 50 ml suspension having a mass concentration of 5%, and then dropping 5 ml of the glucose ethanol solution into the suspension, stirring the reaction at room temperature for 1 hour, and then evaporating the solvent. It was added to an inert gas-protected muffle furnace and reacted at 900 ° C for 1 hour to obtain carbon-coated lithium sulfide.

(4) 100 mg of carbon-coated lithium sulfide and 1 mg of graphene were added to tetrahydrofuran, and ultrasonically reacted for 3 hours, and then the solvent was evaporated to obtain a graphene/carbon-coated doped lithium sulfide composite.

Example 3

(1) 100 mg of commercial lithium sulfide was mixed with 2.5 mg of copper oxide powder in an inert gas-protected glove box, and then ball milled for 1 hour at a ball mill speed of 2000 rpm to obtain lithium nanosulfide.

(2) The starch was added to ethanol under stirring to dissolve to form a starch ethanol solution having a mass concentration of 7%.

(3) Dispersing the obtained nano lithium sulfide into an ethanol solution, continuously stirring to form a 50 ml suspension having a mass concentration of 6%, and then dropwise adding 10 ml of the starch ethanol solution to the suspension, stirring the reaction at room temperature for 2 hours, and then evaporating the solvent. It was added to an inert gas-protected muffle furnace at 850 ° C for 3.5 hours to obtain carbon-coated lithium sulfide.

(4) 100 mg of carbon-coated lithium sulfide and 5 mg of graphene were added to tetrahydrofuran, and ultrasonically reacted for 1 hour, and then the solvent was evaporated to obtain a graphene/carbon-coated doped lithium sulfide composite.

Example 4

(1) 100 mg of commercial lithium sulfide was mixed with 1 mg of alumina powder in an inert gas-protected glove box, and then ball-milled for 2 hours in a ball mill at a ball milling speed of 1000 rpm to obtain lithium nanosulfide.

(2) The cellulose was added to ethanol under stirring to dissolve to form a cellulose ethanol solution having a mass concentration of 6%.

(3) Dispersing the obtained nano lithium sulfide into an ethanol solution, continuously stirring to form a 50 ml suspension having a mass concentration of 7%, and then dropping 25 ml of the cellulose ethanol solution into the suspension, stirring the reaction at room temperature for 3 hours, and then evaporating. The solvent was added to an inert gas-protected muffle furnace at 820 ° C for 4 hours to obtain carbon-coated lithium sulfide.

(4) 100 mg of carbon-coated lithium sulfide and 3 mg of graphene were added to tetrahydrofuran, ultrasonically reacted for 2 hours, and then the solvent was evaporated to obtain a graphene/carbon coated doped lithium sulfide composite.

Example 5

(1) 100 mg of commercial lithium sulfide and 3 mg of nickel oxide powder were mixed in an inert gas-protected glove box, and then ball-milled for 1.5 hours in a ball mill at a ball milling speed of 1,500 rpm to obtain lithium nano-sulphide.

(2) Sucrose was added to ethanol under stirring to dissolve to form a sucrose ethanol solution having a mass concentration of 8%.

(3) Dispersing the obtained nano lithium sulfide into an ethanol solution, continuously stirring to form a 50 ml suspension having a mass concentration of 8%, and then dropping 30 ml of the sucrose ethanol solution into the suspension, stirring the reaction at room temperature for 4 hours, and then evaporating the solvent. It was added to an inert gas-protected muffle furnace and reacted at 870 ° C for 3 hours to obtain carbon-coated lithium sulfide.

(4) 100 mg of carbon-coated lithium sulfide and 7 mg of graphene were added to tetrahydrofuran, ultrasonically reacted for 2.5 hours, and then the solvent was evaporated to obtain a graphene/carbon coated doped lithium sulfide composite.

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, 1mol/L LiN03 is an additive, assembled into a button-type battery in a filled glove box, and a constant current charge and discharge test is performed using a Land battery test system. . The charge and discharge voltage range is 1-3V, the current density is 0.1C, and the performance is shown in Table 1.

Table 1

[Table 1]

1 is an SEM image of a positive electrode material prepared according to the present invention. It can be seen from the figure that the carbon-coated lithium sulfide particles are uniformly distributed on the surface of the graphene, which is beneficial to improving 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 graphene/carbon coated doped lithium sulfide composite material having a core-shell structure, comprising the following steps:

Step (1): mixing commercial lithium sulfide with metal oxide powder in an inert gas-protected glove box, and then loading it into a sealed ball-milling tank, and then loading it into a ball mill for ball milling to obtain doped nano-lithium sulfide;

Step (2): adding a carbon source to the ethanol under stirring, and dissolving to form an ethanol solution containing a carbon source;

Step (3): dispersing the obtained nano lithium sulfide into an ethanol solution, continuously stirring to form a suspension, and then adding an ethanol solution containing a carbon source to the suspension, stirring the reaction at room temperature, then evaporating the solvent, adding to the inertia Reacting in a gas-protected muffle furnace to obtain carbon-coated lithium sulfide;

Step (4) Adding carbon-coated lithium sulfide and graphene to tetrahydrofuran, ultrasonically reacting, and then evaporating the solvent to obtain a core-shell structured graphene/carbon coated doped lithium sulfide composite.
The method according to claim 1, wherein the mass ratio of lithium sulfide to metal oxide in the step (1) is 100:0.5-5.
The method according to claim 1, wherein the metal oxide in the step (1) is one or more of magnesium oxide, manganese dioxide, copper oxide, aluminum oxide, and nickel oxide.
The method according to claim 1, wherein the ball milling time in the step (1) is from 0.5 to 3 hours, and the ball milling speed is from 500 to 3,000 rpm.
The method according to claim 1, wherein the organic carbon source in the step (2) is one or more of sucrose, glucose, starch, cellulose; and the mass concentration of the ethanol solution containing the carbon source is formed. It is 5-10%.
The method according to claim 1, wherein the step (3) the lithium sulfide ethanol solution has a mass concentration of 5-10%; and the volume ratio of the carbon source ethanol solution to the lithium sulfide ethanol solution is 1:1. ; stirring at room temperature for 1-5 hours, in a muffle furnace The reaction temperature is 800-900 ° C; the reaction time is 1-5 hours.
The method according to claim 1, wherein the mass ratio of graphene to carbon-coated lithium sulfide in the step (4) is 1:10-100; and the ultrasonic time is 0.5-3 hours.