A carbon-based composite positive electrode material for lithium-sulfur batteries and a preparation method thereof

Abstract

The present invention discloses a carbon-based composite positive electrode material for a lithium-sulfur battery and a preparation method thereof, belonging to the technical field of lithium-sulfur batteries. The method uses a hydrothermal carbonization product of sugar as a precursor, obtains a carbon-based matrix through high-temperature carbonization treatment, and uses an impregnation method to load platinum nanoparticles onto the surface of the matrix to prepare a carbon-based composite material. The method of the present invention involves a simple preparation process, controllable costs, good repeatability, and is suitable for large-scale production. The carbon-based composite positive electrode material prepared by this method has a high specific surface area, alleviates volume expansion during charging and discharging, and promotes the conversion of lithium polysulfide, effectively suppresses the shuttle effect in the battery, and improves the cycle and rate performance of the lithium-sulfur battery.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-sulfur batteries, and in particular to a carbon-based composite positive electrode material for a lithium-sulfur battery and a preparation method thereof. Background Art

[0002] Lithium-ion batteries play a key role in mobile devices (electric vehicles, drones, smartphones, computers, etc.). However, the energy density of traditional lithium-ion battery systems is limited (140 to 260 Wh kg -1 ) and the production cost is high (>$100kW -1 h -1 ), it is difficult to meet the growing needs of electronic equipment, so it is imperative to develop a new type of high-energy electrochemical energy storage system.

[0003] Theoretical specific capacity of lithium-sulfur battery (1675mAh g -1 ), weight specific capacity (2600Wh kg -1 ) are significantly ahead of commercial lithium-ion batteries and are a new energy storage system that is close to practical application and has great prospects. After years of development, lithium-sulfur batteries are still limited by the dendrite growth of metallic lithium, poor conductivity of active sulfur, the "shuttle effect" of lithium polysulfide, volume expansion and other problems. During the charge and discharge process, lithium polysulfide accumulates in the electrolyte near the positive electrode and "shuttles" to the negative electrode under the action of concentration gradient and electric field, causing irreversible loss of active sulfur and large-scale consumption of electrolyte. Therefore, the shuttle effect problem is the most prominent, which is the main bottleneck affecting the actual energy density and cycle life of lithium-sulfur batteries and restricting their industrialization process.

[0004] Researchers have conducted extensive research on inhibiting the shuttle effect. Currently, strategies such as physical confinement, chemical adsorption, and heterostructure composites are being used to optimize the design of cathode materials for lithium-sulfur batteries. However, porous materials such as carbon nanotubes have limited confinement effects on lithium polysulfides and also suffer from problems such as high electrolyte consumption. Chemical adsorption strategies often use transition metal compounds such as Nb2O5, VS2, and NV, but still suffer from poor conductivity and limited chemical adsorption capacity. Therefore, the rational design and construction of new cathode materials to inhibit the shuttle effect in lithium-sulfur batteries and improve their cycle performance are crucial for the practical application and industrialization of lithium-sulfur batteries. Summary of the Invention

[0005] In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide a carbon-based composite positive electrode material for lithium-sulfur batteries and a preparation method thereof, aiming to achieve rapid conversion of lithium polysulfide and efficient suppression of the shuttle effect, thereby improving the energy density and charge-discharge cycle performance of the lithium-sulfur battery positive electrode.

[0006] To achieve the above object, the technical solutions adopted by the present invention are as follows:

[0007] A method for preparing a carbon-based composite positive electrode material for a lithium-sulfur battery. The method uses a hydrothermal carbonization product of sugar as a precursor, obtains a carbon-based matrix through high-temperature carbonization treatment, and uses an impregnation method to load platinum nanoparticles onto the surface of the matrix to prepare a carbon-based composite material.

[0008] The method specifically comprises the following steps:

[0009] (1) Hydrothermal carbonization and high-temperature carbonization of sugar: dissolve sugar in deionized water to prepare a sugar solution with a certain molar ratio; place the sugar solution in a hydrothermal reactor and react at a temperature of 160-200°C for 8-20 hours to obtain a sugar polycondensation precursor; place the obtained sugar polycondensation precursor in a tube furnace and carbonize it at a high temperature under inert gas protection, with a carbonization temperature of 700-1000°C, a heating rate of 5°C / min, and a carbonization time of 30-240 minutes; after carbonization, a carbon-based matrix is ​​obtained;

[0010] (2) Preparation of platinum nanoparticles: Using an alcohol reduction method, ethylene glycol is used as a solvent and a reducing agent to prepare a certain concentration of ethylene glycol solution of platinum salt and ethylene glycol solution of sodium hydroxide. The ethylene glycol solution of platinum salt and the ethylene glycol solution of sodium hydroxide are mixed evenly. The resulting mixed solution is placed in an oil bath at 160-200°C in a nitrogen atmosphere and refluxed for 2-12 hours to obtain a colloidal solution of platinum nanoparticles.

[0011] (3) Preparation of carbon-based composite materials: Platinum nanoparticles were loaded onto a carbon-based matrix by an impregnation method, specifically: an appropriate amount of a colloidal solution of the platinum nanoparticles and 0.1 to 0.5 g of a carbon-based matrix were weighed, an appropriate amount of ethanol was added and fully mixed, ultrasonically dispersed, and stirred for 12 h; the obtained mixture was filtered, and the filtered product on the filter membrane was placed in an oven at 60°C and dried for 12 h to obtain a carbon-based composite material;

[0012] (4) Preparation of positive electrode materials: Weigh a certain amount of carbon-based composite material and sublimed sulfur, grind them evenly, and then put them into a reactor, which is kept warm at 155°C for 12 hours. Grind the obtained black solid, mix it with the conductive agent Super P, the binder PVDF, and the solvent NMP in a certain proportion, stir it thoroughly, and then coat it on aluminum foil. After vacuum drying at 60°C for 12 hours, the carbon-based composite positive electrode material for lithium-sulfur batteries is obtained.

[0013] In the above step (1), the sugar may be a polysaccharide, a disaccharide or a monosaccharide.

[0014] In the above step (1), the molar ratio of the sugar to deionized water is 1:50 to 1:200.

[0015] In the above step (2), the platinum salt is selected from one of chloroplatinic acid, platinum acetylacetonate, platinum tetrachloride, and sodium chloroplatinate.

[0016] In the above step (2), when the ethylene glycol solution of the platinum salt and the ethylene glycol solution of the sodium hydroxide are mixed, the molar ratio of the platinum salt to the sodium hydroxide is 1:20 to 1:100.

[0017] In the above step (3), the loading amount of the platinum nanoparticles is 0.05-0.5 wt %; the colloidal solution of the platinum nanoparticles is measured according to the loading amount.

[0018] In the above step (4), the mass ratio of the carbon-based composite material to the sublimated sulfur is (6-8):(2-4).

[0019] In the above step (4), the mass ratio of the black solid, the conductive agent Super P, and the binder PVDF is (7-9): (0.5-2): (0.5-1).

[0020] Compared with the prior art, the advantages and effects of the present invention are:

[0021] 1. The carbon-based materials designed in the present invention have low-cost and abundant raw materials. Ordinary sugars such as sucrose and glucose can be used as reaction raw materials. The synthesis process is green, pollution-free and environmentally friendly. In addition, the overall preparation process of the composite positive electrode material is simple and highly reproducible, making it suitable for large-scale production.

[0022] 2. The carbon-based matrix in the present invention has a high specific surface area and contains a large number of nano-scale pores on the surface, which can provide sufficient confined space for lithium polysulfide. In addition, this porous structure allows volume expansion during charging and discharging, which is beneficial to the cycle stability of the battery. At the same time, the carbon-based matrix has a high degree of carbonization, which ensures the conductivity of the electrode material.

[0023] 3. The present invention introduces platinum nanoparticles as electrocatalysts to accelerate the conversion process of the intermediate product lithium polysulfide, effectively suppressing the shuttle effect during the charge and discharge process, which can effectively reduce the internal resistance of the battery and improve the battery cycle and rate performance; the loading amount of platinum nanoparticles is a few thousandths or even lower. The ultra-low loading amount can effectively control costs and ensure the practicality of the electrode material.

[0024] 4. The carbon-based composite cathode material prepared by the present invention has relatively high cycle and rate performance, outstanding comprehensive performance, and can be used as the cathode of lithium-sulfur batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is the XRD pattern of the carbon-based matrix material of the present invention;

[0026] Figure 2The XRD pattern of the carbon-based composite material loaded with platinum nanoparticles according to the present invention;

[0027] Figure 3 is a nitrogen desorption adsorption curve diagram of the carbon-based matrix material of the present invention;

[0028] Figure 4 This is a nitrogen desorption and adsorption curve diagram of the platinum nanoparticle-loaded carbon-based composite material of the present invention;

[0029] Figure 5 is a pore size distribution curve diagram of the carbon-based matrix material of the present invention;

[0030] Figure 6 is a pore size distribution curve of the platinum nanoparticle-loaded carbon-based composite material of the present invention;

[0031] Figure 7 This is a rate performance diagram of the carbon-based matrix material of the present invention;

[0032] Figure 8 This is a rate performance diagram of the carbon-based composite cathode material of the present invention;

[0033] Figure 9 This is a cycling performance diagram of the carbon-based matrix material of the present invention at a current density of 0.2C;

[0034] Figure 10 This is a graph showing the cycling performance of the carbon-based composite cathode material of the present invention at a current density of 0.2C. DETAILED DESCRIPTION

[0035] The present invention will be further described in detail below with reference to specific embodiments and accompanying drawings, which are intended to explain rather than limit the present invention.

[0036] The present invention provides a method for preparing a carbon-based composite positive electrode material for a lithium-sulfur battery. The carbon-based composite material is prepared by combining a high-temperature carbonization method and an impregnation method, thereby achieving rapid conversion of lithium polysulfide and effective suppression of the shuttle effect.

[0037] Example 1:

[0038] (1) Hydrothermal carbonization and high-temperature carbonization of sugars: Sucrose was dissolved in deionized water to prepare a 0.5 M sucrose solution, which was placed in a hydrothermal reactor and reacted at 180°C for 12 h to obtain a sugar polycondensation precursor; the above precursor was placed in a tubular furnace and carbonized at high temperature under inert gas protection at a carbonization temperature of 950°C, a heating rate of 5°C / min, and a carbonization time of 30 min.

[0039] (2) Preparation of positive electrode material: The carbon-based matrix material and sublimed sulfur were weighed in a mass ratio of 7:3, ground evenly, and then loaded into a reactor, which was kept warm at 155°C for 12 hours. The obtained black solid was ground and mixed with the conductive agent Super P and the binder PVDF in a mass ratio of 7:2:1. NMP was added, and the mixture was thoroughly stirred and coated onto aluminum foil. The mixture was vacuum-dried at 60°C for 12 hours to obtain the carbon-based matrix positive electrode material of the present invention.

[0040] The obtained carbon-based matrix material was characterized by X-ray diffractometer (Rigaku D / MAX-2400) and specific surface area and porosity analyzer (TriStarⅡ3020). The electrochemical performance of the button cell assembled with the carbon-based matrix positive electrode material was measured by Xinwei battery testing system (CT-4800). Figure 1 is the XRD pattern of the carbon-based matrix material of the present invention, Figure 3 is a nitrogen desorption adsorption curve diagram of the carbon-based matrix material of the present invention, Figure 5 is a pore size distribution curve of the carbon-based matrix material of the present invention, Figure 7 is a rate performance diagram of the carbon-based matrix material of the present invention, Figure 9 This is a graph showing the cycling performance of the carbon-based matrix material of the present invention at a current density of 0.2C.

[0041] As can be seen from the figure, the carbon-based matrix material has a high degree of graphitization, and the BET test results show that its specific surface area is 340.7m 2 g -1 , the surface contains a large number of pores; the electrochemical performance test results show that the discharge capacity of the carbon-based matrix cathode material at current densities of 0.1C, 0.2C, 0.5C, 1C, and 2C is 678.9mAh g -1 、571.3mAh g -1 , 459.7mAhg -1 、339.6mAh g -1 、164.7mAh g -1 The first cycle discharge capacity is 520.8 mAh g at a current density of 0.2C. -1 After 500 cycles, the discharge capacity remains at 187.5 mAh g -1 The capacity decay rate per cycle is 0.128%.

[0042] Example 2:

[0043] (1) Hydrothermal carbonization and high-temperature carbonization of sugars: Sucrose was dissolved in deionized water to prepare a 0.5 M sucrose solution, which was placed in a hydrothermal reactor and reacted at 180°C for 12 h to obtain a sugar polycondensation precursor; the above precursor was placed in a tubular furnace and carbonized at high temperature under inert gas protection at a carbonization temperature of 950°C, a heating rate of 5°C / min, and a carbonization time of 30 min.

[0044] (2) Preparation of platinum nanoparticles: Using alcohol reduction method, ethylene glycol was used as solvent and reducing agent, and chloroplatinic acid was used as platinum salt. 0.135 g of chloroplatinic acid hexahydrate was dissolved in 50 ml of ethylene glycol to prepare 0.005 M chloroplatinic acid ethylene glycol solution. 0.3 g of sodium hydroxide was dissolved in 15 ml of ethylene glycol to prepare 0.5 M sodium hydroxide ethylene glycol solution. The two were mixed evenly and placed in an oil bath at 160 ° C under nitrogen protection and refluxed for 4 h. After constant volume, 0.5 mg ml -1 colloidal solution of platinum nanoparticles.

[0045] (3) Preparation of carbon-based composite materials: Platinum nanoparticles were loaded onto the carbon-based matrix by the impregnation method. 10 ml of the above-mentioned colloidal solution and 0.1 g of the carbon-based matrix were measured and thoroughly mixed with 20 ml of ethanol. After being dispersed evenly by ultrasonic vibration, the mixture was stirred for 12 h. The mixed solution was filtered and the filtered product on the filter membrane was placed in an oven at 60°C and dried for 12 h to obtain the carbon-based composite material.

[0046] (4) Preparation of positive electrode material: The carbon-based composite material and sublimed sulfur were weighed in a mass ratio of 7:3, ground evenly, and then loaded into a reactor, and kept warm at 155°C for 12 hours; the obtained black solid was ground, mixed with the conductive agent Super P and the binder PVDF in a mass ratio of 7:2:1, NMP was added, and the mixture was fully stirred and coated on aluminum foil, and vacuum dried at 60°C for 12 hours to obtain the carbon-based composite positive electrode material for lithium-sulfur batteries according to the present invention.

[0047] The obtained carbon-based composite materials were characterized by X-ray diffractometer (Rigaku D / MAX-2400) and specific surface area and porosity analyzer (TriStarⅡ3020). The electrochemical performance of the button cells assembled with the carbon-based composite cathode materials was measured using a Xinwei battery test system (CT-4800). Figure 2 is the XRD pattern of the platinum nanoparticle-loaded carbon-based composite material of the present invention, Figure 4 This is a nitrogen desorption adsorption curve of the platinum nanoparticle-loaded carbon-based composite material of the present invention. Figure 6 is a pore size distribution curve of the carbon-based composite material loaded with platinum nanoparticles according to the present invention, Figure 8 This is a rate performance diagram of the carbon-based composite cathode material of the present invention. Figure 10This is a graph showing the cycling performance of the carbon-based composite cathode material of the present invention at a current density of 0.2C.

[0048] As can be seen from the figure, the carbon-based matrix material has a high degree of graphitization, and the BET test results show that its specific surface area is 274.3m 2 g -1 , the surface contains a large number of pores; the electrochemical performance test results show that the discharge specific capacity of the carbon-based matrix positive electrode material at current densities of 0.1C, 0.2C, 0.5C, 1C, and 2C is 991.9mAh g -1 , 772.2mAh g -1 、572.0mAhg -1 、472.1mAh g -1 、324.9mAh g -1 The first cycle discharge capacity is 900.4 mAh g at a current density of 0.2C. -1 After 500 cycles, the discharge capacity remains at 355.1 mAh g -1 The capacity decay rate per cycle is 0.121%.

[0049] From the above implementation cases, it can be seen that the carbon-based composite positive electrode material loaded with electrocatalyst nanoparticles prepared by the method of the present invention effectively suppresses the shuttle effect during the charge and discharge process, exhibits a high discharge capacity and good cycle stability, and at the same time, the preparation process is simple, the cost is controllable, and it is suitable for large-scale preparation and production. It can be used as a positive electrode material for lithium-sulfur batteries and play a role in portable devices such as drones, mobile phones, and computers.

[0050] The foregoing description shows and describes preferred embodiments of the present invention. However, as previously stated, it should be understood that the invention is not limited to the form disclosed herein and should not be construed as excluding other embodiments. Rather, the invention is applicable to various other combinations, modifications, and environments and is capable of modification within the scope of the inventive concept described herein, through the teachings above, or through techniques or knowledge in the relevant art. Modifications and variations made by those skilled in the art that do not depart from the scope of the invention are intended to be within the scope of the appended claims.

Claims

1. A method for preparing a carbon-based composite cathode material for a lithium-sulfur battery, characterized in that: This method uses the hydrothermal carbonization product of sugar as a precursor, obtains a carbon-based matrix through high-temperature carbonization treatment, and uses an impregnation method to load platinum nanoparticles onto the surface of the matrix to produce a carbon-based composite material. The method specifically comprises the following steps: (1) Hydrothermal carbonization and high-temperature carbonization of sugar: dissolve sugar in deionized water to prepare a sugar solution with a certain molar ratio; place the sugar solution in a hydrothermal reactor and react at a temperature of 160-200°C for 8-20 hours to obtain a sugar polycondensation precursor; place the obtained sugar polycondensation precursor in a tube furnace and carbonize it at a high temperature under the protection of inert gas at a carbonization temperature of 700-1000°C, a heating rate of 5°C / min, and a carbonization time of 30 minutes; after carbonization, a carbon-based matrix containing nano-scale pores is obtained; (2) Preparation of platinum nanoparticles: Using the alcohol reduction method, ethylene glycol is used as a solvent and a reducing agent to prepare a certain concentration of ethylene glycol solution of platinum salt and ethylene glycol solution of sodium hydroxide. The ethylene glycol solution of platinum salt and the ethylene glycol solution of sodium hydroxide are mixed evenly. In a nitrogen atmosphere, the obtained mixed solution is placed in an oil bath at 160-200°C and refluxed for 2-12 hours to obtain a colloidal solution of platinum nanoparticles. (3) Preparation of carbon-based composite materials: Platinum nanoparticles are loaded onto a carbon-based matrix by an impregnation method, specifically: an appropriate amount of colloidal solution of the platinum nanoparticles is measured, wherein the loading amount of the platinum nanoparticles is 0.05-0.5 wt %; 0.1-0.5 g of the carbon-based matrix is ​​weighed, an appropriate amount of ethanol is added and fully mixed, ultrasonically dispersed, and stirred for 12 h; the obtained mixture is filtered, and the filtered product on the filter membrane is placed in an oven at 60 ° C and dried for 12 h to obtain a carbon-based composite material; (4) Preparation of positive electrode materials: Weigh a certain amount of carbon-based composite material and sublimed sulfur, grind them evenly and put them into a reactor, and keep them warm at 155°C for 12 hours; grind the obtained black solid, mix it with the conductive agent Super P, binder PVDF, and solvent NMP in a certain proportion, stir it thoroughly and coat it on aluminum foil, and vacuum dry it at 60°C for 12 hours to obtain the carbon-based composite positive electrode material for lithium-sulfur batteries.

2. The method for preparing a carbon-based composite cathode material for a lithium-sulfur battery according to claim 1, wherein: In step (1), the sugar may be a polysaccharide, a disaccharide or a monosaccharide.

3. The method for preparing a carbon-based composite cathode material for a lithium-sulfur battery according to claim 1, wherein: In step (1), the molar ratio of the sugar to deionized water is 1:50 to 1:

200.

4. The method for preparing a carbon-based composite cathode material for a lithium-sulfur battery according to claim 1, wherein: In step (2), the platinum salt is selected from one of chloroplatinic acid, platinum acetylacetonate, platinum tetrachloride, and sodium chloroplatinate.

5. The method for preparing a carbon-based composite cathode material for a lithium-sulfur battery according to claim 1, wherein: In step (2), when the ethylene glycol solution of platinum salt and the ethylene glycol solution of sodium hydroxide are mixed, the molar ratio of the platinum salt to the sodium hydroxide is 1:20 to 1:

100.

6. The method for preparing a carbon-based composite cathode material for a lithium-sulfur battery according to claim 1, wherein: In step (4), the mass ratio of the carbon-based composite material to the sublimated sulfur is (6-8): (2-4).

7. The method for preparing a carbon-based composite cathode material for a lithium-sulfur battery according to claim 1, wherein: In step (4), the mass ratio of the black solid, the conductive agent Super P, and the binder PVDF is (7-9): (0.5-2): (0.5-1).

8. A carbon-based composite positive electrode material for a lithium-sulfur battery prepared by the preparation method according to any one of claims 1 to 7.

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