CN107140633A - A kind of preparation method and applications of the activated carbon with high specific surface area of biomass derived - Google Patents

Abstract

A kind of preparation method and applications of the activated carbon with high specific surface area of biomass derived, belong to preparation and the lithium-sulfur cell technical field of carbon material.Present invention utilizes biomass castoff --- and palm shell passes through charing, activation, rinsing and dry easy steps, you can obtain the activated carbon with high specific surface area of biomass derived as carbon source.Activated carbon and sulphur are mixed and carry out attached reaction of Salmon-Saxl, the composite of palm shell activated carbon and sulphur is obtained；Again by the composite of palm shell activated carbon and sulphur and conductive carbon black, Kynoar mixed dissolution in N-methyl pyrrolidones, mixed slurry is formed；Then mixed slurry is coated on aluminium foil, through drying, the positive electrode of lithium-sulfur cell is made.Obtained activated carbon has high-specific surface area, pore-size distribution concentration, high absorption property and high electrochemical performance.

Description

A kind of preparation method and application of biomass-derived ultra-high specific surface area activated carbon

technical field

The invention belongs to the technical field of carbon material preparation and also relates to the technical field of lithium-sulfur batteries.

Background technique

Relying on traditional, non-renewable, and limited energy consumption or production of fossil fuel combustion is not only a necessary condition for the rapid development of the world economy, but also leads to increasingly serious environmental pollution, global warming, and the aggravation of energy crises. Therefore, environmental pollution and Energy supply has become the two most important issues. From the viewpoint of social sustainability and environmental friendliness, the use of porous carbon materials as electrode materials in lithium-sulfur batteries has attracted increasing attention.

Lithium-sulfur batteries have attracted attention in fields such as electric vehicle applications due to their very high electrical energy density. However, the poor electronic/ionic conductivity of elemental sulfur severely limits its practical application in electrodes. Another problem with lithium-sulfur batteries is that the reduction of S produces various soluble long _- chain polysulfides ( _Li2Sn , _4≤n≤8 ), which further combine with Li to form insoluble and insulating _Li2S2 / _Li2S precipitation. This undesirable phenomenon not only leads to low Coulombic efficiency and loss of active materials, but also hinders the accessibility of ions. The improvement of the conductivity of sulfur electrodes and the suppression of ion diffusion in organic electrolytes will become the focus of lithium-sulfur battery research.

Nanostructured carbon materials with high specific surface area, large pore volume, and porous structure, such as mesoporous carbon, carbon nanotubes, porous graphene, hollow carbon spheres, and activated carbon, are suitable substrates for elemental sulfur. The carbon framework provides a good conductive network for sulfur intercalation and deintercalation, and the nanoporous structure can induce the diffusion of polymers. Therefore, various activation methods (physical and chemical activation) can be used to synthesize and prepare microstructures of porous carbon materials. In particular, the chemical activation of various carbon sources using KOH as an activator is very promising because of its lower activation temperature and higher yield, as well as well-defined micropore size distribution and up to 3000 m ^g Porous carbon with ultra-high specific surface area around ^-1 .

Fossil-based carbon sources are limited and non-renewable, thus there is an urgent need to develop various renewable, abundant natural biomass as well as derivatives and wastes as economical, environmentally friendly carbon sources for the preparation of activated carbon.

Palm shell is a large amount of solid waste discharged from palm oil production plants. It originated in Africa and is now widely planted in tropical regions, especially in the Malay Peninsula. If these wastes are randomly discarded during processing, it will not only waste resources, but also cause environmental pollution.

Contents of the invention

The purpose of the present invention is to propose a method for preparing biomass-derived ultra-high specific surface area activated carbon from palm shells.

The present invention comprises the following steps:

1) After carbonizing the palm shells in a nitrogen environment, they are pulverized to obtain carbonized palm shell powder;

2) Mix the carbonized palm shell powder with the activator, and then dry it at 100±10°C to obtain the palm shell powder containing the activator;

3) Place the palm shell powder containing the activator in a nitrogen atmosphere, activate it at a temperature of 800-1000°C, and cool it to obtain activated palm material;

4) The activated palm material was rinsed with hydrochloric acid aqueous solution and deionized water to neutrality, and then dried to obtain black powdery solid particles, that is, activated carbon with ultra-high specific surface area derived from biomass.

The invention utilizes the biomass waste——palm shell as the carbon source. Because palm shell is hard and contains a small amount of ash, lignin and cellulose, it can be used as a low-cost carbon source as waste biomass, and it is also a high-quality activated carbon precursor raw material. The invention can obtain the activated carbon with ultra-high specific surface area derived from biomass through the simple steps of carbonization, activation, rinsing and drying. The prepared activated carbon has high specific surface area, concentrated pore size distribution, high adsorption performance and high electrochemical performance.

Compared with prior art, the advantage of process of the present invention is:

1. Palm shell is rich in raw materials and low in cost. The use of biomass waste palm shells as raw materials to prepare high-performance activated carbon not only comprehensively utilizes biomass recyclable raw materials, but also facilitates the control of air pollution and water pollution. In today's energy shortage, it is in line with people's pursuit of green, conservation and environmental protection.

2. The biomass porous activated carbon prepared by activation has a simple preparation process and can effectively improve the performance of the carbon-sulfur composite electrode. The porous pores of the obtained activated carbon can not only fully contact with the insulating material sulfur to improve the high conductivity of the carbon-sulfur composite, but also can absorb and store polysulfides during the discharge process, thereby preventing polysulfides from dissolving in the electrolyte. Furthermore, suitable meso-macropores facilitate the rapid transport and diffusion of ions into the micropores during electrochemical cycling and significantly prevent the aggregation of sulfur. Therefore, composite porous carbons in lithium-sulfur batteries show their capacitive performance is superior to ordinary porous carbons.

Further, the temperature environment of the carbonization treatment in step 1) of the present invention is 500±20°C. Pre-carbonization is performed by directly pyrolyzing the carbon source precursor under inert gas conditions, so that the matrix is transformed into a porous carbon solid material with a specific structure that can be controlled. During the carbonization process, the density of the carbon material increases gradually. In the early stage of pre-carbonization, certain pores will be formed due to the escape of small molecules, and the number of pores begins to increase. If the carbonization temperature is too high, the pore structure of the carbonized material will be destroyed, and the structure will collapse to a certain extent, so that the activator cannot enter the deep pores for activation, resulting in a decrease in the performance of the prepared activated carbon; if the carbonization temperature is too low , the pores of the carbonized material will not be fully opened due to incomplete pre-carbonization, which will also lead to uneven activation of the activator, which will reduce the performance of the prepared activated carbon. Therefore, it is more reasonable to choose the temperature environment of carbonization treatment as 500±20°C.

The activator in the step 2) is KOH. The most widely used activator is KOH solution. The unactivated carbonized material has a small amount of macropores and the surface is loose. The pore structure is conducive to the rapid entry of the activator (KOH) for activation and pore formation, therefore, it is beneficial to obtain ultra-high specific surface area and pore volume. Among them, when the temperature is lower than 500°C, it is mainly the dehydration process of carbon materials; when the temperature is lower than 762°C (the boiling point of potassium), the activation is mainly carried out by the reaction of KOH and amorphous carbon to form potassium carbonate. To consume a large amount of carbon particles, thereby forming a large number of pore void structures in the carbon matrix; when the temperature continues to rise beyond the boiling point of potassium, potassium will become potassium vapor at high temperature, and the carbon material will be engraved to enhance the activation effect.

The mixing mass ratio of carbonized palm shell powder and KOH in the step 2) is 3-5:1. Generally speaking, if the amount of carbonized palm shell powder is too large, the activated carbon will have too much activator and the reaction between the carbon and the activator will be too violent, and some mesopores will be expanded into macropores, reducing the mesopore structure. , resulting in a decrease in performance; and if the amount of carbonized palm shell powder is too small, it will be difficult for the activator to fully react with the carbonized material to fully expand the pores due to too little activator, so that the carbonized material cannot be fully activated and the pores are smaller. If the mixing effect of alkali-carbon ratio is just right, the activator can fully play the role of pore-forming and pore-enlarging in the activation process, and accelerate the activation reaction of carbonized material, so that the specific surface area of activated carbon increases rapidly, and the pore volume also increases. further increase. At the same time, it can reduce the amount of raw materials used and the cost of preparing activated carbon to a certain extent, reduce the activation temperature, activation time and alkali-carbon ratio, and reduce the energy consumption of the entire process.

The activation time in step 3) is 1 h. On the premise that the activation temperature and alkali-carbon ratio remain unchanged, if the activation time is too long, the reaction time between carbon and potassium oxide will be prolonged, so that more carbonized materials will react during the activation process, and the pores in the activated carbon will be blocked. Capacity expansion will eventually lead to a decrease in the number of micropores in activated carbon; too short an activation time will result in too short a reaction time between potassium hydroxide and carbon, resulting in an incomplete activation process and insufficient activation of the carbonized material, making the activated carbon Many pore structures are not fully opened, and the number of micropores in activated carbon is reduced. Moreover, the large pores and loose structure of the carbonized material enable the activator to perform etching and pore-forming reactions with carbon atoms faster and better, shortening the time of the activation reaction. This also shows that activation time has relatively little effect on activated carbon.

Another object of the present invention is to propose the application of the above-prepared activated carbon in lithium-sulfur batteries.

First mix the activated carbon and sulfur and then carry out the sulfur-attaching reaction to obtain a composite material of palm shell activated carbon and sulfur; then mix and dissolve the composite material of palm shell activated carbon and sulfur with conductive carbon black and polyvinylidene fluoride in nitrogen-methyl pyrrolidone to form a mixed slurry; then the mixed slurry is coated on an aluminum foil and dried to make a positive electrode material for a lithium-sulfur battery.

After testing, in the electrolyte solution, the lithium-sulfur battery assembled with the positive electrode material as the working electrode, the metal lithium sheet as the negative electrode separator and the Celgard-2250 polypropylene membrane has the following characteristics:

Experiments show that: palm shell activated carbon has a specific surface area of 2760m ² /g and a pore volume of 1.6cm ³ /g, and the prepared porous carbon with a large specific surface area is conducive to better penetration of the positive electrode material into the electrolyte. C/S composites with different sulfur contents after mixing palm shell activated carbon and sulfur element in different proportions. The C/S composite with a sulfur content of 60% has an initial reversible capacity of 945mAh/g at a current density of 200mA/g, and exhibits excellent cycle performance. After 100 cycles, the reversible capacity can still maintain 822mAh/g. High, good cycle stability. The Coulombic efficiency of the battery can be maintained above 95% during the initial cycle.

In addition, the mixing mass ratio of the activated carbon and sulfur is 1:1.5-4. Since the electronic conductivity of elemental sulfur is very low, it can hardly be directly used as the positive electrode of lithium-sulfur batteries, so it is necessary to compound it with high-conductivity materials to improve the electronic conductivity of the surface of active sulfur materials. At present, the main solution is to properly dope elemental sulfur, by introducing a high-conductivity matrix into the sulfur cathode material, and it can have a good adsorption effect on polysulfides, such as porous carbon. Usually the amount of attached sulfur is mainly calculated based on the pore volume of the prepared activated carbon, the mass of the porous carbon is calculated from the pore volume and density of the porous carbon, and the mass of the attached elemental sulfur is obtained according to the S/C molar mass fraction and the sulfur attached rate is calculated. The calculated sulfur addition rate is 58.2%. It is generally believed that the performance of lithium-sulfur batteries can only be improved when the sulfur content in the positive electrode material is not less than 60%, so the preferred mixing mass ratio of activated carbon and sulfur in the present invention is 1:1.5-4.

The sulfur addition reaction is carried out at 155°C. Since the elemental sulfur melts into a molten state during the heat treatment process at 155°C, the fluidity is the best and the effect of fully filling the pore structure is the best, which can increase the contact area and help improve performance. If the temperature is too high, the structure of sulfur begins to break. As the temperature continues to rise, the vapor pressure increases so that the liquid sulfur gradually turns into sulfur vapor and escapes. At 400°C, most of the sulfur element escapes from the matrix in the form of sulfur vapor.

In addition, on the positive electrode material of lithium-sulfur battery, in order to solve the non-conductive problem of elemental sulfur, generally by adding a conductive carrier with high conductivity and high specific surface area, that is, the prepared palm shell porous carbon is compounded with elemental sulfur to increase the positive electrode material. Excellent conductivity and shorten the diffusion path of lithium ions and electrons, which is conducive to the rapid charge and discharge process of the battery. Simple mixing of carbon source and sulfur directly leads to low battery capacity and rapid attenuation. Therefore, in this experiment, an appropriate amount of acetylene black conductive agent is added to the electrode composite material, which can promote electron transfer and establish a good conductive network, so that the reaction has sufficient Reactivity, to improve the conductivity of the overall electrode material; and introduce an appropriate amount of polyvinylidene fluoride as a binder for preparing the slurry, through its bonding effect to maintain the structural stability of the sulfur electrode material, so that the sulfur-containing powder material is bonded to the Together. Excessive binder content will result in low conductivity of the sulfur-containing cathode material, which will reduce the utilization rate of sulfur and the discharge specific capacity of the sulfur electrode. At the same time, the content of the binder in the sulfur electrode should not be too small, otherwise, the sulfur-containing powder of the positive electrode will easily fall off the current collector during the charging and discharging process of the battery, resulting in a decrease in the utilization rate of sulfur and the discharge specific capacity of the sulfur electrode. Considering various factors, the preferred mixing mass ratio of composite material, conductive carbon black and polyvinylidene fluoride in the present invention is 8:1:1.

Description of drawings

Fig. 1 is the SEM image of the field emission scanning electron microscope of the composite material after adding sulfur to the biomass-derived ultra-high specific surface area activated carbon prepared in the present invention.

Fig. 2 is a field emission transmission electron microscope TEM image of the composite material of the biomass-derived ultra-high specific surface area activated carbon with sulfur attached prepared by the present invention.

Fig. 3 is an X-ray diffraction XRD pattern of the composite material of the biomass-derived ultra-high specific surface area activated carbon with sulfur addition prepared in the present invention.

Fig. 4 is the X-ray photoelectron spectrum XPS diagram of the composite material of the biomass-derived ultra-high specific surface area activated carbon with sulfur attached prepared by the present invention.

Fig. 5 is the cyclic voltammetry curve of the test of the composite material of the biomass-derived ultra-high specific surface area activated carbon prepared by the present invention after sulfur addition is applied to the lithium-sulfur battery.

Fig. 6 is a galvanostatic charge-discharge curve of the tested biomass-derived ultra-high specific surface area activated carbon with sulfur added to the lithium-sulfur battery.

Fig. 7 is a cycle curve diagram of the test of the composite material of the biomass-derived ultra-high specific surface area activated carbon prepared by the present invention after sulfur addition is applied in a lithium-sulfur battery.

Fig. 8 is a comparison chart of the cycle performance curves of lithium-sulfur batteries obtained when the amount of added sulfur is 40:60, 30:70 and 20:80.

detailed description

The experimental process of the present invention is described in detail below, aiming to make the design process, design purpose, innovations and advantages of the present invention more clear.

1. Preparation of activated carbon:

example 1:

1. Carbonization:

Weigh the dried palm shell raw material and place it in a quartz crucible, then put it into a tube furnace for heating, and in a nitrogen-enclosed environment, raise the temperature in the tube furnace to 500±20 °C at a heating rate of 5 °C/min Carbonization treatment 2h.

After the completion, let it stand and cool to normal temperature, then take it out to obtain black palm shell carbonized material, which is crushed and sieved to obtain carbonized palm shell powder with a particle size of ≤10 μm, and set aside.

2. Dipping:

Weigh the carbonized palm shell powder and mix it with KOH at a mass ratio of 3:1, add an appropriate amount of distilled water, stir evenly, and place it in an oven at 100±10°C to dry to obtain palm shell powder containing an activator.

3. Activation:

Put the palm shell powder containing the activator in a nickel crucible, and then put it into a tube furnace. Under nitrogen atmosphere, raise the temperature in the tube furnace to 800 °C at a heating rate of 5 °C/min, and keep the temperature Activate for 1 h. It is then cooled to obtain activated palm feed.

4. Washing and drying:

The activated palm material is rinsed with hydrochloric acid aqueous solution and deionized water to neutrality to remove the residual activator in the activated carbon, and then dried by suction filtration to obtain a black powdery solid particle, which is a biomass-derived ultra-high specific surface area activated carbon. And marked as: activated carbon 1#, activated carbon 2#, activated carbon 3#.

The concentration of the above hydrochloric acid aqueous solution is 1 M, and its pH value is 6-8.

Example 2:

1. Carbonization:

Weigh the dried palm shell raw material and place it in a quartz crucible, then put it into a tube furnace for heating, and in a nitrogen-enclosed environment, raise the temperature in the tube furnace to 500±20 °C at a heating rate of 5 °C/min Carbonization treatment 3h.

After the completion, let it stand and cool to normal temperature, then take it out to obtain black palm shell carbonized material, which is crushed and sieved to obtain carbonized palm shell powder with a particle size of ≤10 μm, and set aside.

2. Dipping:

Weigh the carbonized palm shell powder and mix it with KOH at a mass ratio of 5:1, add an appropriate amount of distilled water, stir evenly, and dry in an oven at 100±10°C to obtain palm shell powder containing an activator.

3. Activation:

Put the palm shell powder containing the activator in a nickel crucible, and then put it into a tube furnace. Under a nitrogen atmosphere, raise the temperature in the tube furnace to 1000 °C at a heating rate of 5 °C/min, and keep the temperature Activate for 1 h. It is then cooled to obtain activated palm feed.

4. Washing and drying:

The activated palm material is rinsed with hydrochloric acid aqueous solution and deionized water to neutrality to remove the residual activator in the activated carbon, and then dried by suction filtration to obtain a black powdery solid particle, which is a biomass-derived ultra-high specific surface area activated carbon. And marked as: activated carbon 4#, activated carbon 5#, activated carbon 6#.

The concentration of the above hydrochloric acid aqueous solution is 1 M, and its pH value is 6-8.

Example 3:

Biomass-derived ultra-high specific surface area activated carbons were prepared in a similar manner to the above example, and were marked as: activated carbon 7#, activated carbon 8#, and activated carbon 9#.

2. Application:

Example 1:

1. Preparation of carbon-sulfur composite materials:

The activated carbon and sulfur prepared in Example 1 were mixed, wherein the mass ratios of activated carbon and sulfur were respectively set to 40:60, 30:70 and 20:80.

Then the mixture was heated in a sealed polytetrafluoroethylene reactor at 155°C for 12 hours, and after grinding, black palm shell activated carbon and sulfur composite materials were obtained, which were respectively marked as AC/S-60 and AC/S -70 and AC/S-80.

2. Preparation of electrode sheets:

According to the mass ratio of 8:1:1, the composite material of palm shell activated carbon and sulfur, conductive carbon black (Super P, as a conductive agent) and polyvinylidene fluoride (5% PVDF, as a binder) were mixed in N- Methylpyrrolidone (NMP, as a dispersant) solvent, ground and stirred to prepare a slurry. The slurry was coated on aluminum foil with a film applicator, and dried in a vacuum oven at 50 °C for 2 h, and the dried electrode sheet was taken out and punched into an electrode sheet with a diameter of 9 mm as a working electrode.

3. Battery assembly:

Assembly was performed in a glove box (Universal 2440/750, MIKROUNA) under an argon atmosphere (oxygen and water pressures < 1 ppm) using 2032-type coin cells. The electrolyte solution is a mixture of 1 M LiN (CF ₃ SO ₂ ) ₂ (LiTFSI) dissolved in dimethoxyethane (DME) and dioxolane (DOL), the negative electrode is metal lithium sheet, and the diaphragm is Celgard-2250 type polypropylene film.

Example 2:

The activated carbon prepared in Example 2 was mixed with sulfur, and assembled into a battery according to the method in Example 1.

Example 3:

The activated carbon prepared in Example 3 was mixed with sulfur, and assembled into a battery according to the method in Example 1.

3. Product characteristics:

Figure 1 shows the SEM image of the field emission scanning electron microscope SEM image of the biomass-derived ultra-high specific surface area activated carbon 5# sulfur-attached composite material prepared in Example 2 of the present invention, and the activated carbon has developed and abundant irregular pores , while no accumulation of bulk sulfur was found on the surface of the sulfur-attached composites, suggesting that sulfur was fully incorporated into the porous carbon matrix by capillary forces during heating.

Figure 2 shows the field emission transmission electron microscope TEM image of the biomass-derived ultra-high specific surface area activated carbon 5# sulfur-attached composite material prepared in Example 2 of the present invention. After 60% (w) of sulfur attached, the TEM of the composite material The images indicated that the amorphous sulfur phase components were trapped in the pores of the activated carbon matrix, and no large volume sulfur was observed in the composite, indicating that elemental sulfur was uniformly dispersed in the porous carbon matrix.

Fig. 3 has shown the X-ray diffraction XRD pattern of the super high specific surface area activated carbon 5# of biomass derivation prepared in the embodiment of the present invention 2 and the composite material after adding sulfur, and the XRD collection of illustrative plates of activated carbon shows about 25 ° and 43 °, and this Corresponding to (002) and (100) diffractograms of amorphous carbon. Figure 3 also shows that the activated carbon prepared in Example 2 has no obvious crystallization peaks related to sulfur in the XRD pattern of the composite material after sulfur addition, indicating that sulfur is in a highly dispersed state in the pores.

Figure 4 shows the X-ray photoelectron spectrum XPS diagram of the biomass-derived ultra-high specific surface area activated carbon 5# sulfur-attached composite material prepared in Example 2 of the present invention. The surface element composition of the prepared carbon material was analyzed by XPS. The prepared carbon material obviously contains three elements: N, S, and P. At the same time, the composite material after sulfur addition also contains a relatively high S element, thus proving that The S element was doped into the prepared composite material, and the sulfur was attached successfully, and the elemental sulfur was uniformly distributed in the skeleton of the porous carbon matrix.

Figures 5, 6 and 7 respectively show the electrochemical performance test curves of the biomass-derived ultra-high specific surface area activated carbon 5# prepared in Example 2 of the present invention after adding sulfur and applying the composite material to a lithium-sulfur battery.

Figure 5 shows the cyclic voltammetry curves. In the first cycle, two reduction peaks and one oxidation peak were observed, which is due to the multi-step reaction mechanism of sulfur and lithium. In the second cycle, the cathodic and anodic peaks are still evident, which is attributed to the polarization of the electrode material in the first cycle.

Figure 6 is a graph of the galvanostatic charge-discharge curve, which shows the typical voltage capacity of the composite electrode after sulfur addition to activated carbon at 200 mA/g during the initial two cycles. The discharge curve shows two typical voltage capacities at 2.3 and 2.1V. platform, which can be assigned to the two-step reaction of sulfur with lithium during discharge. For the composite electrode with sulfur attached to activated carbon, an initial discharge capacity of 945 mAh/g was obtained.

Figure 7 is the cycle curve, the cycle performance graph of the activated carbon/sulfur composite electrode at 200 mA/g, after 100 cycles, the discharge capacity is still maintained at 822 mAh/g, indicating good cycle stability. The Coulombic efficiency of the cell remained above 95% upon initial cycling.

In addition, when other conditions are the same, only changing the mass ratio of activated carbon and sulfur in the preparation of the working electrode, such as 40:60, 30:70 and 20:80, the performance of the lithium-sulfur battery is different. .

Due to the ultra-high specific surface area and large pore volume of porous carbon, the battery cycle performance and sulfur utilization rate have been significantly improved. However, a high carbon-sulfur mass ratio does not necessarily correspond to a high discharge specific capacity.

Figure 8 is a comparison chart of the cycle performance curves of lithium-sulfur batteries obtained when the amount of added sulfur is 40:60, 30:70 and 20:80, respectively. When the sulfur load is 60%, the initial discharge capacity of the battery can reach 945mAh/g at a high current density of 200mmA/g, and after 100 cycles, the discharge capacity is still maintained at 822mAh/g, and the coulombic efficiency of the battery can be maintained Above 95%, it shows that the cycle stability is good. For lithium-sulfur batteries with 70% and 80% sulfur attached, the discharge capacity is reduced, because the sulfur content is too high, the resistivity of the compound also increases correspondingly, which will cause the utilization rate of sulfur to decrease. To a certain extent, improving the conductivity of carbon-sulfur composites can increase the discharge specific capacity of the corresponding battery.

It can be seen that the present invention prepares palm shell activated carbon with superior performance at a suitable alkali-carbon ratio and heating temperature. After characterizing and testing the performance of activated carbon prepared under different proportions and different temperatures, the best performance conditions are obtained, and sulfur addition is carried out. applied to lithium-sulfur batteries.

Claims (9)

1. A preparation method of biomass-derived ultra-high specific surface area activated carbon, characterized in that it may further comprise the steps: 1) After carbonizing the palm shells in a nitrogen environment, they are pulverized to obtain carbonized palm shell powder; 2) Mix the carbonized palm shell powder with the activator, and then dry it at 100±10°C to obtain the palm shell powder containing the activator; 3) Place the palm shell powder containing the activator in a nitrogen atmosphere, activate it at a temperature of 800-1000°C, and cool it to obtain activated palm material; 4) The activated palm material was rinsed with hydrochloric acid aqueous solution and deionized water to neutrality, and then dried to obtain a biomass-derived ultra-high specific surface area activated carbon. 2. The preparation method according to claim 1, characterized in that: the temperature environment of the carbonization treatment in the step 1) is 500±20°C. 3. The preparation method according to claim 1, characterized in that: the activator in the step 2) is KOH. 4. The preparation method according to claim 3, characterized in that the mixing mass ratio of the carbonized palm shell powder and KOH in the step 2) is 3-5:1. 5. The preparation method according to claim 3, characterized in that: the activation time in the step 3) is 1 h. 6. The application of the biomass-derived ultra-high specific surface area activated carbon prepared by the method as claimed in claim 1 in lithium-sulfur batteries is characterized in that: firstly, the activated carbon and sulfur are mixed to carry out sulfur-attachment reaction to obtain palm shell A composite material of activated carbon and sulfur; then mix and dissolve the composite material of palm shell activated carbon and sulfur with conductive carbon black and polyvinylidene fluoride in nitrogen-methylpyrrolidone to form a mixed slurry; then coat the mixed slurry on aluminum foil After drying, it is made into the positive electrode material of lithium-sulfur battery. 7. The application according to claim 6, characterized in that: the mixing mass ratio of activated carbon and sulfur is 1:1.5-4. 8. The application according to claim 6 or 7, characterized in that the sulfur addition reaction is carried out at 155°C. 9. The application according to claim 6, characterized in that the mixing mass ratio of the composite material to conductive carbon black and polyvinylidene fluoride is 8:1:1.