WO2016192389A1

WO2016192389A1 - Lithium sulfur battery composite positive electrode material and preparation method thereof

Info

Publication number: WO2016192389A1
Application number: PCT/CN2015/099570
Authority: WO
Inventors: 周成冈; 周吟; 闫允潘; 韩波; 吴金平
Original assignee: 中国地质大学（武汉）
Priority date: 2015-06-03
Filing date: 2015-12-29
Publication date: 2016-12-08
Also published as: CN104900880B; CN104900880A

Abstract

The present invention relates to a lithium sulfur battery composite positive electrode material and a preparation method thereof. The lithium sulfur battery composite positive electrode material is prepared by using a conductive agent having a mesoporous structure, sulfur, and a modifying agent. The sulfur is dispersed in holes of the conductive agent, the modifying agent is connected to orifices of the conductive agent by using a chemical bonding manner, and the mass ratios of the components are: 30% to 59.4% of the conductive agent, 40% to 60% of the sulfur, and 0.1% to 10% of the modifying agent. The preparation method thereof comprises: pouring sulfur into a conductive agent by adopting a molten suction method, to obtain a conductive agent/sulfur composite material; and then modifying the obtained conductive agent/sulfur composite material, to obtain a lithium sulfur battery composite positive electrode material. The composite positive electrode material not only can implement excellent high-rate stability performance, but also can effectively reduce the loss of active substances and the influence such as lithium negative electrode corrosion and rapid capacity attenuation caused by a "shuttle effect" due to dissolution of lithium polysulfide, thereby remarkably increasing the cycle performance of a lithium sulfur battery.

Description

Lithium-sulfur battery composite cathode material and preparation method thereof

Technical field

The invention relates to the technical field of lithium-sulfur batteries, in particular to a lithium-sulfur battery composite cathode material and a preparation method thereof.

Background technique

The monosulfide cathode material is electrochemically reacted with S ₈ +16Li→8Li ₂ S, and its specific capacity is as high as 1675 mAh·g ^-1 . It is the highest energy density in the known solid cathode material, and the sulfur is abundant in reserves, low in price and safe. Low toxicity, so it has a very broad application prospects. However, since the sulfur element is an electronic insulator (5×10 ^-30 S·cm ^-1 , 25 ° C), and the high-valent lithium polysulfide formed during the discharge process (the lithium-sulfur battery is at different discharge voltages, lithium reacts with sulfur to form Lithium polysulfide with different valence sulfur, the products formed from high valence state to low valence state are Li ₂ S ₈ , Li ₂ S ₆ , Li ₂ S ₄ , Li ₂ S ₃ , Li ₂ S ₂ , Li ₂ S ) Soluble in the electrolyte, forming a so-called "shuttle effect" which seriously affects the battery life and affects the application of lithium-sulfur batteries in actual production. The shuttle effect caused by the dissolution of polysulfide significantly reduces sulfur utilization, specific capacity and cycle performance, while increasing the viscosity of the electrolyte and the migration resistance of ions; as the discharge progresses, the final product of the poor conductivity discharge Li ₂ S and Li ₂ S ₂ may cover the surface of the positive electrode active material in the form of a solid film, thereby hindering the electrochemical reaction between the electrolyte and the electrode active material. Therefore, how to suppress the diffusion of polysulfide and improve the conductivity during the sulfur cathode cycle is the research focus of lithium-sulfur battery cathode materials.

Aiming at the research of cathode materials, it has achieved good results in improving the cycle performance of lithium-sulfur batteries under low discharge rate. In order to solve the problem of unstable structure of the cathode due to volume change during charge and discharge, a series of measures have also been taken. However, at high discharge rates, maintaining high initial capacity and improving cycle performance have not been well resolved. This is mainly because as the discharge rate increases, the degree of electrochemical polarization and concentration polarization will seriously affect the efficiency of the electrode. Therefore, in order to ensure the normal operation of the lithium-sulfur battery cathode material at a high rate, the cathode material must be performed. The design not only needs to provide a large number of ion transport channels, so that lithium ions can be efficiently embedded and removed, and it is also necessary to suppress the dissolution loss of polysulfide and improve the cycle performance of the positive electrode material.

Summary of the invention

The technical problem to be solved by the present invention is to provide a lithium-sulfur battery composite positive electrode material having a high initial capacity and good cycle performance at a high discharge rate and a preparation method thereof, in view of the above-mentioned deficiencies in the prior art.

In order to solve the above technical problem, the technical solution provided by the present invention is:

Provided is a lithium-sulfur battery composite cathode material comprising a conductive agent having a mesoporous structure, sulfur and a modifier dispersed in a pore of a conductive agent, wherein the modifier is chemically bonded and electrically conductive The pores of the agent are connected, and the mass ratio of each component is 30 to 59.4% of the conductive agent, 40 to 60% of the sulfur, and 0.1 to 10% of the modifier.

According to the above scheme, the conductive agent is a mesoporous carbon material having a pore size distribution of 2-10 nm, a specific surface area of 500-800 m ² /g, and a hydrophilic functional group at the opening of the cell; the modifier is glucose, galactose One of deoxyribose.

According to the above scheme, the mesoporous carbon material is obtained by activation of a carbon material by preparing a solid KOH and a carbon material uniformly mixed at a mass ratio of 1-5:1, and then placing it in a tube furnace with hydrogen gas and The mixed gas of nitrogen is a protective atmosphere in which the volume ratio of hydrogen is 1-5%, calcined at 650-850 ° C for 0.5-1.5 h, and then the calcined product is washed successively with dilute hydrochloric acid and deionized water until neutral, and finally dried to obtain a medium. Hole carbon material.

According to the above scheme, the carbon material is a multi-walled carbon nanotube, a carbon nanofiber or a carbon nanosphere.

According to the above aspect, the hydrophilic functional group is a hydroxyl group or a carboxyl group.

The invention also provides a preparation method of the above lithium-sulfur battery composite cathode material, the steps of which are as follows:

1) Preparation of conductive agent/sulfur composite material: the conductive agent and sulfur are ground and uniformly mixed, placed under N ₂ atmosphere, and heated to 155-160 ° C at room temperature at a rate of 5-10 ° C / min, and kept for 5-10 h. Then, the temperature is raised to 190-210 ° C for 5 to 5 hours at a rate of 5-10 ° C / min, and the conductive agent/sulfur composite material is naturally cooled, and the mass ratio of the conductive agent to the sulfur in the conductive agent/sulfur composite material is 0.5-1.5: 1;

2) preparing a lithium-sulfur battery composite cathode material: dissolving the modifier in ultrapure water to obtain a modifier aqueous solution having a concentration of 2.22×10 ^-5 -2.22×10 ^-3 mol/L, and adding the step 1 to the modifier aqueous solution The obtained conductive agent/sulfur composite material is ultrasonically treated to uniformly disperse the conductive agent/sulfur composite material in the aqueous solution of the modifier to obtain a uniform dispersion, and the obtained dispersion liquid is transferred to the hydrothermal reaction kettle at 100-140 The reaction of °C for 4-24h, after the completion of the reaction, the solid product is separated to obtain the composite material of lithium-sulfur battery. The mass ratio of each component in the composite material of lithium-sulfur battery is 30~59.4% of conductive agent and 40~60% of sulfur. The agent is 0.1 to 10%.

According to the above scheme, the conductive agent in the step 1) is a mesoporous carbon material having a pore diameter of 2-10 nm, a specific surface area of 500-800 m ² /g, and a hydrophilic functional group at the opening of the pore.

In another preferred embodiment, the modifying agent is a polyhydroxy sugar.

In another preferred embodiment, the modifying agent is selected from the group consisting of a monosaccharide, a disaccharide, an oligosaccharide, or a combination thereof.

In another preferred embodiment, the modifying agent is one of glucose, galactose, and deoxyribose.

According to the above scheme, the hydrophilic functional group is a hydroxyl group and a carboxyl group.

According to the above scheme, the sonication time of step 2) is 30-60 min, and the ultrasonic frequency is 20-25 kHz.

The principle of the invention is that the conductive agent of the invention is a mesoporous structure, the electrochemically active substance sulfur is dispersed in the pores of the conductive agent, and the modifying agent (sugar) is chemically bonded to the active part of the orifice of the conductive agent. Connect to adjust the performance of the orifice. The modification of the composite by the saccharide radical generated by the hydrothermal reaction of glucose and the like ensures that the lithium-sulfur cathode material selectively allows passage of lithium ions and inhibits the passage of polysulfide ions. On the one hand, the sugar radicals at the pores have a certain adsorption effect on the lithium polysulfide, which prevents the polysulfide from overflowing from the pores and dissolves; on the other hand, the hydrophilic radicals of the carbohydrate radicals and the mesoporous carbon pores The chemical bonding has a shrinkage effect, and the size of the orifice is adjusted to some extent, and the passage of polysulfide is inhibited to some extent without affecting the free passage of lithium ions having a small radius, thereby hindering the dissolution of lithium polysulfide.

It should be understood that in the present invention, the above action mechanism is merely for explaining the present invention, but the mechanism of action of the positive electrode material of the present invention is not limited to the above explanation.

Compared with the prior art, the present invention mainly has the following advantages: First, the modifier (saccharide) used in the experiment can be achieved when the content is very low (the mass ratio in the composite positive electrode material is 0.6%). Very good cycle stability effect, which greatly reduces the loss of energy density of the positive electrode material; second, hydrothermal decomposition of sugars into hydrophilic radicals of mesoporous carbon material orifices for orientation Chemical bonding can ensure the uniform dispersion and distribution of carbohydrate radicals on the positive electrode material. Third, the chemical bonding of the carbohydrate free radicals with the hydrophilic functional groups of mesoporous carbon pores can ensure the efficiency of carbohydrate free radicals. The use of the channel selectively allows lithium ions to be efficiently embedded and removed to inhibit the passage of polysulfide ions, thereby improving the cycle performance of the lithium-sulfur battery.

The beneficial effects of the invention are as follows: 1. The preparation method of the invention is simple, and the prepared lithium-sulfur battery composite cathode material is chemically bonded with a hydrophilic radical generated by a saccharide decomposition reaction such as glucose and a hydrophilic functional group at a mesoporous carbon hole. Effectively inhibiting the dissolution of polysulfide under the premise of free passage of lithium ions; 2. The invention greatly increases the transmission channel of lithium ions by activating carbon materials (carbon nanotubes, carbon nanofibers or carbon nanospheres). The lithium ion can be quickly embedded and removed, so that the material can be quickly charged and discharged, and has high rate performance, and the use of the modifier makes the lithium-sulfur battery using the composite positive electrode material prepared by the invention have high rate stability performance and can effectively reduce the capacity. The loss and the "shuttle effect" caused by the "shuttle effect" caused by the dissolution of lithium polysulfide caused the corrosion of the lithium negative electrode and the rapid decay of the capacity, thereby significantly improving the cycle performance of the lithium-sulfur battery (the capacity retention rate was increased from 48.64% to 64.01-92.26%). .

DRAWINGS

1 is a discharge cycle test chart of a battery assembled with a lithium-sulfur battery composite positive electrode material prepared in Comparative Example 1, Comparative Example 2, Comparative Example 3, and Example 2;

2 is a cycle test diagram of a battery assembled with a composite positive electrode material of a high-rate performance lithium-sulfur battery prepared in Example 1, Example 2, Example 3, and Example 4;

3 is a battery discharge cycle test chart of a composite positive electrode material of a high-rate performance lithium-sulfur battery prepared in Example 5;

4 is a graph showing the discharge rate of a battery assembled with a composite positive electrode material of a high-rate performance lithium-sulfur battery prepared in Example 6. FIG.

detailed description

In order to make those skilled in the art better understand the technical solutions of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

Comparative example 1

A conductive agent/sulfur composite cathode material is prepared as follows:

1) Weigh 0.2g of multi-walled carbon nanotubes (pore size 2-5nm, specific surface area 324m ² /g, pore volume 0.40cm ³ /g) as conductive agent (C), weigh 0.2g of electrochemically active substance Sulfur (S);

2) After the conductive agent and sulfur are ground and mixed uniformly, they are placed in a tube furnace, with N ₂ as the shielding gas, the gas flow rate is set to 50 mL/min, and the temperature is raised to 155 ° C at a rate of 10 ° C/min at room temperature. 10h, then heated to 190 ° C at a rate of 10 ° C / min for 3h, then naturally cooled to obtain a conductive agent / sulfur composite (o-CNT / S);

The above conductive agent/sulfur composite material is prepared into a positive electrode sheet by the following method:

The above conductive agent/sulfur composite material (o-CNT/S) and binder (polyvinylidene fluoride) were uniformly mixed at a mass ratio of 9:1, and then dispersed in N-methylpyrrolidone for magnetic stirring for 12 hours to obtain a positive electrode. The slurry; the obtained positive electrode slurry was coated on an aluminum foil to form a sheet, dried, rolled, and sliced to obtain a desired positive electrode sheet, and the thickness of the positive electrode sheet was 100 μm.

The above positive electrode sheet is assembled into a battery as follows:

The positive electrode is made of the above positive electrode sheet, the negative electrode is made of a lithium foil having a thickness of about 50 μm, the separator is a Celegard 2400 polypropylene film, and the electrolyte is dissolved in lithium bistrifluoromethanesulfonate (LiN(CF ₃ SO ₂ ) ₂ ). In a mixed solution of dimethoxyethane (DME) and 1,3-dioxolane (DOL) (Note: the volume ratio of dimethoxyethane to 1,3-dioxolane in the electrolyte is 1:1, the concentration of lithium bistrifluoromethanesulfonate in one of them is 1 mol/L); the above components are assembled in a cylindrical battery in the structure of a positive electrode/separator/negative electrode, and the entire battery assembly process is in a glove box. carry out.

The battery assembled in this comparative example was subjected to constant current charge and discharge test at a current density of 1 C. The battery test temperature was around room temperature 25 ° C. The test results showed that the first discharge specific capacity of the battery was 712 mAh/g, and the discharge was performed after 200 cycles. The specific capacity was 291 mAh/g, and the results are shown in Fig. 1.

Comparative example 2

A conductive agent/sulfur/glucose composite positive electrode material using glucose as a modifier, wherein the components are used in an amount of 59.4% by weight of a conductive agent, 40% by weight of sulfur, and 0.6% by weight of a modifier.

Specific steps are as follows:

1) Weigh 0.2g of multi-walled carbon nanotubes (o-CNT) (pore size 2-5nm, specific surface area of 324m ² /g, pore volume of 0.40cm ³ /g) as a conductive agent, weigh 0.134g of electrochemical Active substance sulfur;

3) Dissolve glucose in 100 mL of ultrapure water to obtain a glucose aqueous solution having a concentration of 3.33×10 ^-5 mol/L, and add 100 mg of the multi-walled carbon nanotube/sulfur composite prepared in the step 2) to the aqueous glucose solution, and clean it with ultrasonic waves. The instrument is processed to be uniformly dispersed in the aqueous glucose solution, the sonication time is 30 min, and the ultrasonic frequency is 20-25 kHz; after the completion of the ultrasonication, the solution is transferred to a hydrothermal reaction kettle, and reacted at 140 ° C for 24 h to prepare the obtained product. Filtered and dried to finally obtain a multi-walled carbon/sulfur/glucose composite.

The methods for preparing the positive electrode sheet, assembling the battery, and testing the battery in this example were the same as in Comparative Example 1. The battery charge and discharge test results show that the first charge-discharge specific capacity of the battery is 664 mAh/g at 1 C discharge rate, and the specific capacity is 471 mAh/g after 200 cycles. The results are shown in Fig. 1. Compared with Comparative Example 1, the cycle performance is greatly improved, and the electrochemical performance of the battery is also improved. It indicates that the hydrophilic functional group at the pore opening of the multi-walled carbon nanotubes is bonded to the glucose radical to improve the cycle performance of the battery.

Comparative example 3

A lithium-sulfur battery composite cathode material is prepared as follows:

1) weigh 0.24g porous multi-walled carbon nanotubes (h-CNT) as a conductive agent (C), weigh 0.16g of electrochemically active substance sulfur (S);

The above porous multi-walled carbon nanotubes are prepared by using solid potassium hydroxide and multi-walled carbon nanotubes (pore size 2-5 nm, specific surface area 324 m ² /g, pore volume 0.40 cm ³ /g) to 5 The mass ratio of 1: is uniformly mixed, and then placed in a tube furnace, with a mixed gas of hydrogen and nitrogen as a protective atmosphere, wherein the volume ratio of hydrogen is 5%, calcined at 850 ° C for 1.5 h, and then the calcined product is taken out, After washing with 1 mol/L of dilute hydrochloric acid, it is washed with deionized water until neutral. After filtration, it is dried at 80 ° C for 12 h to obtain porous multi-walled carbon nanotubes (h-CNT), which is a mesoporous carbon material (pore size is 2-10 nm). The specific surface area was 800 m ² /g, and the pore volume was 1.06 cm ³ /g).

2) After the conductive agent and sulfur are ground and mixed uniformly, they are placed in a tube furnace, with N ₂ as the shielding gas, the gas flow rate is set to 50 mL/min, and the temperature is raised to 155 ° C at a rate of 10 ° C/min at room temperature. After 10 h, the temperature was raised to 190 ° C for 3 h at a rate of 10 ° C / min, and then naturally cooled to obtain a conductive agent / sulfur composite material (h-CNT / S).

The methods for preparing the positive electrode sheet, assembling the battery, and testing the battery were the same as in Comparative Example 1. It can be seen from Fig. 1 that the first charge-discharge specific capacity of the battery prepared in this example is 1184 mAh/g at a 1 C rate, and the specific capacity after 510 cycles is 576 mAh/g. Compared with Comparative Example 1, the initial capacity of discharge is greatly improved. This is because the carbon material multi-walled carbon nanotubes have a rich pore structure after activation, which accelerates the efficient migration and removal of lithium ions.

Example 1

Preparing a porous multi-walled carbon nanotube/sulfur/glucose composite cathode material using glucose as a modifier, wherein The amount of each component is, in terms of mass percentage, 50 wt% of the conductive agent porous multi-walled carbon nanotubes, 49.9 wt% of the electrochemically active substance sulfur, and 0.1 wt% of the modifier glucose.

The above porous multi-walled carbon nanotubes are prepared by solid potassium hydroxide and multi-walled carbon nanotubes (pore size 2-5 nm, specific surface area 324 m ² /g, pore volume 0.40 cm ³ /g, Nanjing Xian The product is uniformly mixed at a mass ratio of 5:1, and then placed in a tube furnace with a mixture of hydrogen and nitrogen as a protective atmosphere, wherein the volume ratio of hydrogen is 5% and calcined at 850 °C. After 1.5 h, the calcined product was taken out, washed with 1 mol/L of dilute hydrochloric acid, and then washed with deionized water until neutral. After filtration, it was dried at 80 ° C for 12 h to obtain porous multi-walled carbon nanotubes (h-CNT). That is, a mesoporous carbon material (having a pore diameter of 2 to 10 nm, a specific surface area of 800 m ² /g, and a pore volume of 1.06 cm ³ /g).

The specific preparation method is as follows:

1) Weigh 0.2g of porous multi-walled carbon nanotubes (h-CNT) as a conductive agent, weigh 0.198g of electrochemically active substance sulfur;

2) The conductive agent and sulfur weighed in step 1) are ground and uniformly mixed, and then placed in a tube furnace, with N ₂ as a shielding gas, the gas flow rate is set to 50 mL/min, and the temperature is 10 ° C/min at room temperature. Heating to 155 ° C, holding for 10 h, then heating at a rate of 10 ° C / min to 190 ° C for 3 h, then naturally cooled to obtain a conductive agent / sulfur composite (o-CNT / S);

3) hydrothermal method to load the free radical generated by the decomposition of glucose on the porous multi-wall carbon nanotube/sulfur composite material (h-CNT/S);

100 mg porous multi-walled carbon nanotube/sulfur composite (h-CNT/S) prepared by dissolving glucose in 100 mL of ultrapure water to obtain 2.22×10 ^-5 mol/L aqueous glucose solution and adding to glucose aqueous solution in step 2) Ultrasonic cleaning with ultrasonic cleaning device to uniformly disperse in aqueous glucose solution, sonication time is 30min, frequency is 20-25kHz; after ultrasonic completion, the solution is transferred to the reaction kettle, reacted at 140 ° C for 24h, the preparation will be The product is filtered and dried to give a mesoporous carbon/sulfur/glucose composite.

The methods for preparing the positive electrode sheet, assembling the battery, and testing the battery in this example were the same as in Comparative Example 1. The battery charge and discharge test results show that the first charge-discharge specific capacity of the battery is 1088 mAh/g at 1 C discharge rate, and the specific capacity is 697 mAh/g after 200 cycles. The results are shown in Fig. 2. Compared with Comparative Example 3, the first charge-discharge specific capacity is slightly smaller, but the cycle performance is greatly improved. This is because the modification of porous multi-walled carbon nanotubes/sulfur composites hinders the insertion and removal of lithium ions. The effect, because the modifier content is low, the inhibition effect on lithium ion insertion and removal is relatively weak, and the initial capacity is slightly decreased from 1184 mAh/g to 1088 mAh/g.

Example 2

A porous multi-walled carbon nanotube/sulfur/glucose composite positive electrode material prepared by using glucose as a modifier, wherein the amount of each component is as follows: conductive agent porous multi-walled carbon nanotubes 59.4 wt%, electrochemically active substance Sulfur 40% by weight, modifier glucose 0.6% by weight.

The above porous multi-walled carbon nanotubes are prepared by solid potassium hydroxide and multi-walled carbon nanotubes (pore size 2-5 nm, specific surface area 324 m ² /g, pore volume 0.40 cm ³ /g, Nanjing Xian The product is uniformly mixed at a mass ratio of 5:1, and then placed in a tube furnace with a mixture of hydrogen and nitrogen as a protective atmosphere, wherein the volume ratio of hydrogen is 5% and calcined at 650 °C. After 1.5 h, the calcined product was taken out, washed with 1 mol/L of dilute hydrochloric acid, and then washed with deionized water until neutral. After filtration, it was dried at 80 ° C for 12 h to obtain porous multi-walled carbon nanotubes (h-CNT). That is, the mesoporous carbon material, infrared test shows that a large number of hydrophilic functional group hydroxyl groups are formed around the surface pores of the mesoporous carbon material.

The specific preparation method is as follows:

1) Weigh 2g of porous multi-walled carbon nanotubes (h-CNT) as a conductive agent, weigh 1.98g of electrochemically active substance sulfur;

2) The conductive agent and sulfur weighed in step 1) are ground and uniformly mixed, and then placed in a tube furnace with N ₂ as a shielding gas, the gas flow rate is set to 50 mL/min, and the temperature is 5 ° C/min at room temperature. Heating to 160 ° C, holding for 5 h, then heating at a rate of 5 ° C / min to 210 ° C for 5 h, then naturally cooled to obtain a conductive agent / sulfur composite (o-CNT / S);

3.98 g of porous multi-walled carbon nanotube/sulfur composite material prepared by dissolving glucose in 60 mL of ultrapure water to obtain 2.22×10 ^-3 mol/L aqueous glucose solution and adding to glucose aqueous solution in step 2) (h-CNT/ S), ultrasonically ultrasonically sprayed to uniformly disperse in the aqueous glucose solution, the ultrasonic treatment time is 30 min, the frequency is 20-25 kHz; after the completion of the ultrasonication, the solution is transferred to the reaction kettle, and reacted at 100 ° C for 4 h, The prepared product is filtered and dried to finally obtain a mesoporous carbon/sulfur/glucose composite.

The methods for preparing the positive electrode sheet, assembling the battery, and testing the battery in this example were the same as in Comparative Example 1. The battery charge and discharge test results show that the first charge-discharge specific capacity of the battery prepared in this example is 1005mAh/g at 1C rate, and the specific capacity is 793mAh/g after 200 cycles. The cycle test chart of the battery is shown in Figure 2. . Compared with Example 1, a suitable amount of glucose free radicals further enhances its stability.

Example 3

A porous multi-walled carbon nanotube/sulfur/glucose composite cathode material prepared by using glucose as a modifier is similar to that of Example 1, except that the amount of each component is determined by mass percentage: conductive porous multi-wall carbon nanometer The tube was 50% by weight, the electrochemically active substance sulfur was 49.2% by weight, and the modifier glucose was 0.8% by weight.

The preparation method of the composite positive electrode material, the preparation of the positive electrode sheet, the assembly battery and the battery test method in this embodiment are the same as those in the first embodiment. The battery charge and discharge test results show that the first charge and discharge of the battery prepared in this embodiment is at 1 C rate. The specific capacity is 754mAh/g, and the specific capacity is 561mAh/g after 200 cycles. The cycle test chart of the battery is shown in Figure 2. The increase in the glucose content compared to Example 2 resulted in a significant decrease in the initial capacity of the battery system, but the cycle performance was substantially unchanged, and the specific capacity reduction ratio was similar after 200 cycles.

Example 4

A porous multi-walled carbon nanotube/sulfur/glucose composite cathode material prepared by using glucose as a modifier is similar to that of Example 1, except that the amount of each component is determined by mass percentage: conductive porous multi-wall carbon nanometer The tube is 30% by weight, the electrochemically active substance sulfur is 60% by weight, and the modifier glucose is 10% by weight.

The preparation method of the composite positive electrode material, the preparation of the positive electrode sheet, the assembly battery and the battery test method in this embodiment are the same as those in the first embodiment. The battery charge and discharge test results show that the first charge and discharge of the battery prepared in this embodiment is at 1 C rate. The specific capacity is 363 mAh/g, and the specific capacity is 284 mAh/g after 200 cycles. The cycle test chart of the battery is shown in Fig. 2. By further increasing the glucose content compared to Example 3, the initial capacity of the battery system was significantly reduced, but the cycle stability was substantially unchanged, i.e., the ratio of specific capacity reduction after 200 cycles was similar.

Example 5

A porous carbon nanofiber/sulfur/galactose composite cathode material prepared by using galactose as a modifier is similar to that of Example 1, except that the carbon material is carbon nanofiber, the sugar is galactose, and the solid potassium hydroxide is used. It is uniformly mixed with carbon nanofibers (pore size 2-5 nm, specific surface area 300 m ² /g, pore volume 0.30 cm ³ /g) in a mass ratio of 1:1, and a mixed atmosphere of hydrogen and nitrogen is used as a protective atmosphere, wherein The volume ratio of hydrogen is 1%, calcined at 650 ° C for 0.5 h to obtain porous carbon nanofibers (pore size 2-10 nm, specific surface area 500 m ² /g, pore volume 0.74 cm ³ /g), the amount of each component In terms of mass percentage, the conductive agent porous carbon nanofibers are 40% by weight, the electrochemically active substance sulfur is 59.4% by weight, and the modifier galactose is 0.6% by weight.

In the present embodiment, the preparation of the composite positive electrode material, the preparation of the positive electrode sheet, the assembled battery, and the battery test method are the same as in the first embodiment, and the constant current charge and discharge test is performed at a current density of 3 C, and the test temperature is 25 ° C at room temperature. The first discharge specific capacity of the battery prepared in this example was 931 mAh/g, and the discharge specific capacity was 859 mAh/g after 200 cycles, and the battery discharge cycle test chart is shown in FIG. Discharge at 3C rate, battery capacity attenuation is small, battery cycle performance is very good.

Table 1 Charge and discharge test results of the batteries prepared in Examples 1-6 and Comparative Examples

As can be seen from Table 1, the cycle performance of each of the examples was significantly improved as compared with the comparative examples.

Example 6

A porous carbon nanosphere/sulfur/deoxyribose composite cathode material prepared by using deoxyribose as a modifier is similar to that of Example 1, except that the carbon material is carbon nanosphere (pore size 2-6 nm, specific surface area 280 m ^{2 )} /g, pore volume is 0.44 cm ³ /g), the sugar is deoxyribose, and porous carbon nanospheres are obtained by activation (pore size is 2-8 nm, specific surface area is 580 m ² /g, pore volume is 0.78 cm ³ /g) The amount of each component is determined by mass percentage: 50 wt% of conductive agent porous carbon nanospheres, 49.4 wt% of electrochemically active substance sulfur, and 0.6 wt% of modifier deoxyribose.

The preparation of the composite positive electrode material, the preparation of the positive electrode sheet, the assembly battery and the battery test method in this embodiment are the same as those in the first embodiment, respectively, at 0.5C, 1C, 2C, 3C, 4C, 5C, 6C, 7C, 8C, 9C. And constant current charge and discharge test at 10C (10 cycles per cycle), the corresponding capacity is 1084mAh / g, 1010mAh / g, 973mAh / g, 928mAh / g, 812mAh / g, 751mAh / g, 683mAh/g, 644mAh/g, 587mAh/g, 539mAh/g, 511mAh/g, it can be seen that the magnification is reduced from 10C to 0.5C, the capacity is 870mAh/g, the capacity retention rate is 80.25%, and the high rate performance of the battery. Good, the discharge rate diagram of the battery is shown in Figure 4.

Claims

A lithium-sulfur battery composite cathode material characterized in that it consists of a conductive agent having a mesoporous structure, sulfur and a modifier dispersed in a pore of a conductive agent, and the modifier is chemically bonded to The pores of the conductive agent are connected, and the mass ratio of each component is: 30 to 59.4% of the conductive agent, 40 to 60% of the sulfur, and 0.1 to 10% of the modifier.
The lithium-sulfur battery composite cathode material according to claim 1, wherein the conductive agent is a mesoporous carbon material having a pore diameter of 2 to 10 nm, a specific surface area of 500 to 800 m 2 /g, and a pore at the opening of the pore. Aqueous functional groups; and/or

The modifying agent is a polyhydroxy sugar; and/or

The modifying agent is selected from the group consisting of monosaccharides, disaccharides, oligosaccharides, or combinations thereof; and/or

The modifying agent is one of glucose, galactose, and deoxyribose.
The lithium-sulfur battery composite cathode material according to claim 2, wherein the mesoporous carbon material is activated by a carbon material, and the preparation method comprises the following steps: mixing the solid KOH with the carbon material by a mass ratio of 1-5:1. Uniform, then placed in a tube furnace, with a mixture of hydrogen and nitrogen as a protective atmosphere, wherein the hydrogen volume ratio is 1-5%, calcined at 650-850 ° C for 0.5-1.5 h, and then the calcined product is successively diluted with hydrochloric acid Wash with deionized water until neutral, and finally dry to obtain mesoporous carbon material.
The lithium-sulfur battery composite cathode material according to claim 3, wherein the carbon material is a multi-walled carbon nanotube, a carbon nanofiber or a carbon nanosphere.
The lithium-sulfur battery composite positive electrode material according to claim 2, wherein the hydrophilic functional group is a hydroxyl group.
A method for preparing a composite material of a lithium-sulfur battery composite cathode, characterized in that the steps are as follows:

1) Preparation of conductive agent/sulfur composite material: the conductive agent and sulfur are ground and uniformly mixed, placed under N 2 atmosphere, and heated to 155-160 ° C at room temperature at a rate of 5-10 ° C / min, and kept for 5-10 h. Then, the temperature is raised to 190-210 ° C for 5 to 5 hours at a rate of 5-10 ° C / min, and the conductive agent/sulfur composite material is naturally cooled, and the mass ratio of the conductive agent to the sulfur in the conductive agent/sulfur composite material is 0.5-1.485: 1;

2) preparing a lithium-sulfur battery composite cathode material: dissolving the modifier in ultrapure water to obtain a modifier aqueous solution having a concentration of 2.22×10 -5 -2.22×10 -3 mol/L, and adding the step 1 to the modifier aqueous solution The obtained conductive agent/sulfur composite material is ultrasonically treated to uniformly disperse the conductive agent/sulfur composite material in the aqueous solution of the modifier to obtain a uniform dispersion, and the obtained dispersion liquid is transferred to the hydrothermal reaction kettle at 100-140 The reaction of °C for 4-24h, after the completion of the reaction, the solid product is separated to obtain the composite material of lithium-sulfur battery. The mass ratio of each component in the composite material of lithium-sulfur battery is 30~59.4% of conductive agent and 40~60% of sulfur. The agent is 0.1 to 10%.
The method for preparing a lithium-sulfur battery composite cathode material according to claim 6, wherein the conductive agent is a mesoporous carbon material having a pore diameter of 2-10 nm and a specific surface area of 500-800 m 2 /g. And the channel opening has a hydrophilic functional group; the modifier is one of glucose, galactose, and deoxyribose.
The method for preparing a lithium-sulfur battery composite cathode material according to claim 7, wherein the mesoporous carbon material is activated by a carbon material, and the preparation method comprises the following steps: mass ratio of solid KOH to carbon material 5:1 mixed uniformly, and then placed in a tube furnace, with a mixture of hydrogen and nitrogen as a protective atmosphere, wherein the hydrogen volume ratio is 1-5%, calcined at 650-850 ° C for 0.5-1.5h, then the calcined product It is washed with dilute hydrochloric acid and deionized water until neutral, and finally dried to obtain a mesoporous carbon material.
The method for preparing a lithium-sulfur battery composite cathode material according to claim 8, wherein the carbon material is a multi-wall carbon nanotube, a carbon nanofiber or a carbon nanosphere.
The method for preparing a lithium-sulfur battery composite positive electrode material according to claim 7, wherein the hydrophilic functional group is a hydroxyl group.