Preparation method of microporous carbon positive electrode material, microporous carbon positive electrode and secondary battery

Abstract

The invention belongs to the related technical field of sulfur-based batteries, and discloses a preparation method of a microporous carbon positive electrode material, a microporous carbon positive electrode and a secondary battery, and the method comprises the following steps: mixing a carbon source precursor, a solid salt and potassium hydroxide, and carrying out ball milling; carrying out primary heat treatment on the ball-milled material in an inert atmosphere; pickling and drying the material subjected to primary heat treatment to obtain a microporous carbon material; and mixing the microporous carbon material with the positive electrode active material, and carrying out secondary heat treatment in an inert atmosphere to obtain the microporous carbon positive electrode material. According to the invention, the carbon source and the solid salt are mixed for heat treatment, and the molten salt is used as a template to prepare sheet-shaped microporous carbon, so that the positive electrode has a sheet-shaped structure, the cycling stability of the positive electrode can be improved, and the dynamic characteristics and rate capability of the battery can also be improved; kOH is added and primary heat treatment is carried out simultaneously, so that formation of more micropores can be assisted, the content of the positive electrode active material is increased, and the energy density is ensured.

Description

Technical Field

[0001] The present invention belongs to the technical field related to sulfur-based batteries, and more specifically, relates to a preparation method of a microporous carbon cathode material, a microporous carbon cathode, and a secondary battery. Background Art

[0002] The sulfur-based secondary battery is a battery system with sulfur or a sulfur-carbon composite material as the cathode. The theoretical energy density of sulfur is as high as about 2600 Wh / kg, and it has low price and is environmentally friendly. Therefore, this type of battery system has received extensive attention. However, the sulfur cathode is prone to nucleophilic reaction in commercial ester-based electrolytes and loses its electrochemical activity. In ether-based electrolytes, highly soluble polysulfides are easily formed, and the polysulfides will shuttle back and forth between the positive and negative electrodes under the action of an electric field and a concentration gradient (shuttle effect). Not only side reactions will occur on the negative electrode side, but also the continuous loss of the positive electrode active material will be caused. Therefore, the sulfur-based battery often has poor cycle stability and far fails to meet the usage standards of commercial batteries.

[0003] In order to improve the cycle stability of the sulfur-based secondary battery, on the positive electrode side, sulfur can often be fixed on the positive electrode by covalent bonds (chemical sulfur fixation), or sulfur can be confined in micropores by microporous carbon (<2 nm) (physical sulfur fixation). The former often has difficulty avoiding the volume change of sulfur during the redox process, while the latter can slow down the volume change. Therefore, the microporous carbon sulfur cathode is a very promising cathode material for sulfur-based secondary batteries.

[0004] The microporous carbon cathode has requirements for the pore size. Existing research shows that sulfur can be well fixed in ultra-micropores <0.5 nm and exhibits a single plateau of solid-solid conversion during charge and discharge. In addition to the requirements for the pore size of the micropores, there are also requirements for the pore volume of the micropores. Currently, the sulfur content of most microporous carbon sulfur cathode materials is not high, which reduces their competitiveness. In addition, due to the unique pore structure of microporous carbon, the diffusion kinetics of metal ions in the material is hindered, and the rate performance of the battery is often poor. Summary of the Invention

[0005] Aiming at the above defects or improvement requirements of the prior art, the present invention provides a preparation method of a microporous carbon cathode material, a microporous carbon cathode, and a secondary battery, which are used to solve the problem that the diffusion kinetics of metal ions in the existing microporous carbon cathode material is hindered and the rate performance of the battery is often poor.

[0006] To achieve the above object, according to the first aspect of the present invention, a preparation method of a microporous carbon cathode material is provided, including:

[0007] Mix a carbon source precursor, a solid salt, and an alkali metal hydroxide, and then perform ball milling;

[0008] The ball-milled material is subjected to a primary heat treatment in an inert atmosphere;

[0009] The material after the primary heat treatment is pickled and dried to obtain a microporous carbon material;

[0010] The microporous carbon material is mixed with a positive electrode active material and subjected to a secondary heat treatment in an inert atmosphere to obtain a microporous carbon positive electrode material.

[0011] According to the method for preparing a microporous carbon positive electrode material provided by the present invention, the carbon source precursor is a mixture of melamine and p-dibenzaldehyde; wherein, the molar ratio of melamine to p-dibenzaldehyde is 10 / 1 to 1 / 100.

[0012] According to the method for preparing a microporous carbon positive electrode material provided by the present invention, the solid salt is a mixture of LiCl and KCl; wherein, the molar ratio of LiCl to KCl is 10 / 1 to 1 / 100.

[0013] According to the method for preparing a microporous carbon positive electrode material provided by the present invention, the mass ratio of the carbon source precursor to the solid salt is 1 / 5 to 1 / 200; the mass ratio of the carbon source precursor to the alkali metal hydroxide is 100 / 1 to 1 / 100.

[0014] According to the method for preparing a microporous carbon positive electrode material provided by the present invention, the primary heat treatment of the ball-milled material in an inert atmosphere is specifically: in an atmosphere of argon or nitrogen, heat treatment is carried out at a temperature of 100 to 1000 °C for 1 to 24 hours.

[0015] According to the method for preparing a microporous carbon positive electrode material provided by the present invention, the mass ratio of the microporous carbon material to the positive electrode active material is 1 / 0.1 to 1 / 10;

[0016] The secondary heat treatment is specifically: in an atmosphere of argon or nitrogen, heat treatment is carried out at a temperature of 200 °C to 500 °C for 2 to 8 hours.

[0017] According to the method for preparing a microporous carbon positive electrode material provided by the present invention, the positive electrode active material is a compound formed by one or more of sulfur, selenium, tellurium, and iodine.

[0018] According to the method for preparing a microporous carbon positive electrode material provided by the present invention, the positive electrode active material is selenium or a sulfur-selenium compound.

[0019] According to the second aspect of the present invention, there is provided a microporous carbon positive electrode prepared by the method for preparing a microporous carbon positive electrode material described in any one of the above.

[0020] According to the third aspect of the present invention, a secondary battery is provided, which includes the above-mentioned microporous carbon positive electrode, and further includes a negative electrode. The material of the negative electrode is one or more of lithium metal, sodium metal, zinc metal, magnesium metal, aluminum metal, iron metal, lithium copper alloy, lithium aluminum alloy, lithium silicon alloy, lithium silver alloy, graphite, hard carbon, silicon, and silicon carbide.

[0021] Generally speaking, compared with the prior art through the above technical solutions conceived by the present invention, the preparation method of the microporous carbon positive electrode material, the microporous carbon positive electrode, and the secondary battery provided by the present invention are as follows:

[0022] 1. Mixing a carbon source and a solid salt and performing heat treatment, and using the flaky structure formed by the cooling of the molten salt generated during the heat treatment as a template, a flaky microporous carbon can be prepared, so that the prepared positive electrode has a flaky structure, which can not only improve the cycle stability of the positive electrode, but also improve the kinetic characteristics and rate performance of the battery; in addition, adding an alkali metal hydroxide and performing primary heat treatment at the same time, using the physical and chemical effects of the alkali metal hydroxide, is more conducive to pore formation, and can assist in forming more micropores, thereby increasing the content of the positive electrode active material and ensuring the overall energy density of the battery;

[0023] 2. Using melamine and p-dibenzaldehyde as carbon sources is beneficial to the formation of micropores inside the material during the heat treatment process. The microporous carbon positive electrode formed by using melamine and p-dibenzaldehyde as carbon sources can ensure a sufficient content of active substances and the solid-solid transformation of the positive electrode;

[0024] 3. To ensure the overall energy density of the battery, it is often necessary to ensure that the content of the active element is 40% or more to be competitive. The content of the active element in the positive electrode prepared by the present invention can be as high as 50%. This content of the active element is the content in the micropores of the microporous carbon material rather than the surface content. Therefore, on the premise of ensuring a 40% content of the active element and solid-solid transformation, combined with the flaky structure, it is also beneficial to improve the kinetic characteristics of the positive electrode. Description of the Drawings

[0025] Figure 1 is the SEM image of the microporous carbon material without sulfur composite;

[0026] Figure 2 is the charge-discharge curve of the microporous carbon sulfur positive electrode in the lithium-sulfur battery;

[0027] Figure 3 is the cycle curve of the microporous carbon sulfur positive electrode in the lithium-sulfur battery;

[0028] Figure 4 is the discharge curve of the microporous carbon sulfur positive electrode in the sodium-sulfur battery;

[0029] Figure 5It is the cycling curve of the microporous carbon-sulfur cathode using NaFSI as the main electrolyte salt in a sodium-sulfur battery;

[0030] Figure 6 It is the discharge curve of the KB sulfur cathode using NaFSI as the main electrolyte salt in a sodium-sulfur battery;

[0031] Figure 7 It is the cycling curve of the microporous carbon-sulfur cathode using NaPF 6 as the main electrolyte salt in a sodium-sulfur battery;

[0032] Figure 8 It is the cycling curve of the SPAN cathode using NaPF 6 as the main electrolyte salt in a sodium-sulfur battery;

[0033] Figure 9 It is the cycling curve of a sodium-sulfur battery after mixing in a mass ratio of A / B = 1 / 5;

[0034] Figure 10 It is the charge-discharge curve of the microporous carbon / SeS 2 cathode in a sodium-sulfur battery;

[0035] Figure 11 It is the cycling curve of the microporous carbon / SeS 2 cathode in a sodium-sulfur battery;

[0036] Figure 12 It is the charge-discharge curve of the microporous carbon / Se 5 S 3 cathode in a sodium-sulfur battery;

[0037] Figure 13 It is the charge-discharge curve of the microporous carbon / S 8 Se 1 Te 1 cathode in a sodium-sulfur battery;

[0038] Figure 14 It is the charge-discharge curve of the microporous carbon / S 8 Se 1 Te 1 cathode in a sodium-sulfur battery. Detailed implementation manners

[0039] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0040] Please refer to Figure 1, this embodiment provides a method for preparing a microporous carbon cathode material, and the preparation method includes:

[0041] Mix the carbon source precursor, solid salt, and alkali metal hydroxide, and then perform ball milling;

[0042] Perform primary heat treatment on the ball-milled material in an inert atmosphere;

[0043] Pickle and dry the material after primary heat treatment to obtain a microporous carbon material;

[0044] Mix the microporous carbon material with the cathode active material, and perform secondary heat treatment in an inert atmosphere to obtain the microporous carbon cathode material.

[0045] In this embodiment, the carbon source is a carbon-containing compound, and the solid salt can be a chloride salt, which is in a solid state at room temperature. After mixing the two and performing heat treatment, the solid salt appears in a molten state during the heat treatment process. The molten salt can play the role of a "flake template" and help carbon form a nanosheet shape, so that the prepared microporous carbon cathode material has a flake structure, which is beneficial to reducing the diffusion resistance of the cathode active material in the microporous carbon material, thereby improving the battery kinetics performance and the battery rate performance. In addition, the role of adding the alkali metal hydroxide is to create pores and assist in forming more micropores (the definition of micropores is that the pore diameter is less than 2 nm), which is beneficial to increasing the content of the cathode active material and ensuring the overall energy density of the battery.

[0046] Specifically, the alkali metal hydroxide can be a strong alkaline activator, such as potassium hydroxide or sodium hydroxide. Taking potassium hydroxide as an example, the principle of pore formation assisted by the alkali metal hydroxide is as follows: Potassium hydroxide has both physical and chemical pore formation effects. Physical pore formation is achieved by removing potassium hydroxide through subsequent pickling to form pores; chemical pore formation is that during the preparation of microporous carbon, potassium hydroxide (KOH), as a strong alkaline activator, interacts with the carbon precursor through chemical reactions at high temperatures, and can form a rich pore structure, especially micropores (pore diameter < 2 nm). The specific reaction is as follows:

[0047] At high temperatures (usually 600 - 900 °C) and in an inert atmosphere (such as nitrogen), KOH first decomposes to generate K 2 O and H 2 O. The generated H 2 O further reacts with carbon to produce gases (such as H 2 and CO), promoting the oxidative etching of the carbon skeleton; in the presence of carbon oxidation product CO 2 ), K 2 O reacts with CO 2 to form potassium carbonate, which further decomposes at higher temperatures, releasing CO 2 gas and intensifying the etching of the carbon matrix;

[0048] KOH and its decomposition products (such as K 2 O, H 2 O) act as oxidants and react with carbon. These reactions selectively etch the disordered regions in the carbon structure, remove some carbon atoms and generate gases, thereby forming pores;

[0049] At high temperatures, the metallic potassium K generated by the decomposition of KOH inserts into the carbon layers. The insertion of potassium atoms causes the carbon layers to expand and increases the interlayer spacing. Subsequently, the residual potassium salts (such as K 2 CO 3 ) are removed by washing, further releasing pore space and forming a microporous structure;

[0050] Overall, KOH creates pores in carbon materials efficiently through a dual mechanism of chemical etching and physical intercalation.

[0051] Furthermore, solid salts are soluble in water, and alkali metal hydroxides are soluble in acids. Thus, the salts and alkalis in the material after the first heat treatment can be washed away by acid washing to obtain a microporous carbon material. After the first heat treatment, it can be cooled to room temperature before acid washing to avoid oxidation reactions at high temperatures. After cooling after the first heat treatment, a flaky template with a carbon material and an alkali metal hydroxide is obtained, and then the flaky template and the alkali metal hydroxide are removed by acid washing and drying to obtain a microporous carbon material.

[0052] In some specific embodiments, the carbon source precursor is a mixture of melamine and p - dibenzaldehyde; wherein, the molar ratio of melamine to p - dibenzaldehyde is 10 / 1 to 1 / 100. Melamine belongs to N - containing compounds, and the provided N atoms can catalyze the activity of electrochemical reactions; in addition, melamine and p - dibenzaldehyde can form a polymer through the Schiff base reaction, and pyrolyze into porous carbon under heating conditions, which can form more micropores in the microporous carbon material, facilitating ensuring the content of the positive electrode active material in the positive electrode material and improving the competitiveness of the battery.

[0053] In some specific embodiments, the solid salt is a mixture of LiCl and KCl; wherein, the molar ratio of LiCl to KCl is 10 / 1 to 1 / 100. These two salts can stably exist during the subsequent heat treatment process and play a "template" role to help carbon form the shape of nanosheets; at the same time, these two salts and the subsequent alkali metal hydroxides can be washed away (dissolved in water) finally without residue. Moreover, after mixing lithium chloride and potassium chloride, the melting point of the mixture as a whole will decrease, and the overall melting point will be less than the melting points of the individual salts. The two are mixed to form a eutectic melt, which is more conducive to the progress of the first heat treatment process.

[0054] Optionally, the highest temperature during the first heat treatment process can be greater than or equal to the overall melting point of the solid salt.

[0055] In some specific embodiments, the mass ratio of the carbon source precursor to the solid salt is 1 / 5 to 1 / 200; the mass ratio of the carbon source precursor to the alkali metal hydroxide is 100 / 1 to 1 / 100.

[0056] In some specific embodiments, the primary heat treatment of the ball-milled material in an inert atmosphere is specifically as follows: in an atmosphere of argon or nitrogen, heat treatment is carried out at a temperature of 100 to 1000 °C for 1 to 24 hours. Optionally, the primary heat treatment can be carried out by a stepwise heating method, that is, heating is carried out at a plurality of sequentially increasing temperatures while maintaining a preset time at each temperature to fully form a microporous structure. The primary heat treatment is mainly to allow the carbon source to undergo a pyrolysis reaction, and then the final temperature can reach the melting point temperature of the solid salt. Optionally, the specific process of the primary heat treatment is as follows: in an atmosphere of argon or nitrogen, first heat treatment is carried out at 100 - 200 °C for 3 - 5 hours, then at 300 - 500 °C for 1 - 3 hours, and finally at 600 - 800 °C for 1 - 3 hours.

[0057] In some specific embodiments, the mass ratio of the microporous carbon material to the positive electrode active material is 1 / 0.1 to 1 / 10;

[0058] The secondary heat treatment is specifically as follows: in an atmosphere of argon or nitrogen, heat treatment is carried out at a temperature of 200 °C to 500 °C for 2 to 8 hours.

[0059] In some specific embodiments, the positive electrode active material is a compound formed by one or more of sulfur, selenium, tellurium, and iodine. In this embodiment, in addition to the sulfur positive electrode, positive electrodes such as selenium positive electrodes, tellurium positive electrodes, and iodine positive electrodes are also applicable to the microporous carbon positive electrode.

[0060] Optionally, the positive electrode active material is selenium or a sulfur-selenium compound.

[0061] Furthermore, this embodiment provides a microporous carbon positive electrode, which is prepared by the preparation method of the microporous carbon positive electrode material described in any one of the above.

[0062] In some specific embodiments, this embodiment relates to a method of a microporous carbon positive electrode to achieve a solid-phase conversion reaction of a secondary battery and improve the cycle stability of the battery. This embodiment specifically adopts the following technical solutions:

[0063] Mix melamine and p-dibenzaldehyde in a molar ratio of 10 / 1 to 1 / 100 to obtain precursor A;

[0064] Mix LiCl and KCl in a molar ratio of 10 / 1 to 1 / 100 to obtain solid salt B;

[0065] Mix A and B in a mass ratio of 1 / 5 to 1 / 200, and then add KOH in a mass ratio of A to KOH of 100 / 1 to 1 / 100 for mixing, followed by ball milling for 1 to 24 hours;

[0066] The ball-milled material is subjected to a primary heat treatment in a tube furnace under an argon or nitrogen atmosphere at 0 to 1000 °C for 1 to 24 hours;

[0067] Wash the remaining solid salts in the material after the primary heat treatment with dilute hydrochloric acid aqueous solution, dry it, and then mix it with one or more of sulfur, selenium, tellurium, or iodine in a mass ratio of 1 / 0.1 to 1 / 10, and perform heat treatment at 200 °C to 500 °C for 2 to 8 hours in an argon or nitrogen atmosphere to obtain a microporous carbon positive electrode material.

[0068] Furthermore, this embodiment provides a secondary battery, which includes the above-mentioned microporous carbon positive electrode and also includes a negative electrode. The material of the negative electrode is one or more of lithium metal, sodium metal, zinc metal, magnesium metal, aluminum metal, iron metal, lithium copper alloy, lithium aluminum alloy, lithium silicon alloy, lithium silver alloy, graphite, hard carbon, silicon, and silicon carbon. The microporous carbon positive electrode and the negative electrode construct a sulfur-based secondary battery. Preferred negative electrodes are sodium metal and lithium metal.

[0069] To make the implementation schemes and effects of the present invention clearer, the present invention will be further explained below with reference to the accompanying drawings and specific embodiments.

[0070] Example 1:

[0071] In this example, a microporous carbon positive electrode is prepared by mixing A / B / KOH in a mass ratio of 1 / 10 / 1, followed by ball milling, heat treatment, pickling, drying, and then mixing the mixture with sulfur in a mass ratio of 1 / 8, and it is paired with a lithium metal negative electrode to form a lithium-sulfur battery.

[0072] Mix in a mass ratio of A / B / KOH = 1 / 10 / 1, after ball milling, perform heat treatment in an argon or nitrogen atmosphere at 150 °C for 4 hours, 400 °C for 2 hours, and 700 °C for 2 hours to prepare microporous carbon powder. The morphology is as Figure 1 shown. It can be seen that this microporous carbon presents a lamellar morphology. The microporous carbon with this morphological characteristic is beneficial for the diffusion of metal ions inside the material and can improve the kinetic characteristics of the material. Mix this sheet-like microporous carbon with sulfur in a mass ratio of 1 / 8 and then perform secondary heat treatment at 300 °C for 6 hours to obtain a microporous carbon positive electrode material. The prepared microporous carbon positive electrode is assembled with a lithium metal negative electrode to form a lithium-sulfur battery, using LB015 (1M LiPF 6with EC / DEC = 1 / 1 vol% + 5% wt FEC as the electrolyte. During the slurry preparation process, the cathode powder, conductive carbon Super P, and binder LA133 were mixed at a mass ratio of 8 / 1 / 1, and then water was added to form a slurry for slurry preparation and coating. Finally, under the condition that the loading of the cathode active material was 2 mg / cm 2 (the ratio of cathode powder to water was 6 / 25, and the slurry was ball-milled for 6 hours. This loading could be obtained by scraping with a 750-μm blade). Under this condition (the loading of the cathode active material in all examples was controlled to be 2 mg / cm 2 ), its charge-discharge curve at 0.1 A / g was as shown in Figure 2 . Its specific capacity was 513 mAh / g. Since sulfur was stored in the microporous carbon, there was no dissolution of polysulfides and no nucleophilic reaction occurred. Therefore, the battery had high cycle stability, as shown in Figure 3 . As shown, at 0.5 A / g, the capacity of this battery did not decay, indicating that this microporous carbon was a good carbon carrier. The capacity in all examples was calculated based on the whole of carbon + active elements.

[0073] Example 2:

[0074] In this example, a microporous carbon cathode prepared by mixing A / B / KOH at a mass ratio of 1 / 10 / 1, followed by ball-milling, heat treatment, pickling, and drying, and then mixing the mixture with sulfur at a mass ratio of 1 / 8. The sulfur content was obtained as 40% through later elemental analysis (EA) testing. It was paired with a sodium metal anode to form a sodium-sulfur battery, and the electrolyte was NaFSI / DME / TTE = 1 / 1.2 / 1.

[0075] The prepared microporous carbon-sulfur cathode was assembled with sodium metal to form a sodium-sulfur battery, and the electrolyte formula was NaFSI / DME / TTE = 1 / 1.2 / 1. As can be seen from Figure 4 , this cathode presented a single plateau and achieved solid-solid conversion in an ether-based electrolyte. As shown in Figure 5 , at 0.5 A / g, the capacity retention rate of this battery was 82% after 100 cycles.

[0076] Comparative Example 1:

[0077] In this example, KB (Ketjenblack) was used as the carbon carrier to form an existing KB-sulfur cathode. The sulfur content of the KB-sulfur cathode was 40%, and a sodium-sulfur battery was assembled.

[0078] Using the same electrolyte as in Example 2 and on the premise of the same cathode loading, as shown in Figure 6 , this cathode presented multiple discharge plateaus, which was different from the single plateau of the microporous carbon material, and sulfur was not well fixed in the carbon.

[0079] Example 3:

[0080] In this example, a microporous carbon cathode was prepared by mixing A / B / KOH in a mass ratio of 1 / 10 / 1, followed by ball milling, heat treatment, pickling, and drying, and then mixing the resulting mixture with sulfur in a mass ratio of 1 / 8. The sulfur content was 40%, and it was paired with a sodium metal anode to form a sodium-sulfur battery. The electrolyte was 1M NaPF 6 in EC / DEC = 1 / 1 vol% + 5% wt FEC.

[0081] By assembling the sodium-sulfur battery in the same way as in Example 2, the electrolyte was changed from ethers to esters, and the formulation was 1M NaPF 6 in EC / DEC = 1 / 1 vol% + 5% wt FEC. If sulfur is not fixed by the micropores, a nucleophilic reaction will occur and it will be difficult to exert its capacity. As Figure 7 shown, it can be found that not only can the capacity be exerted, but also its stability is relatively high. The capacity retention rate after 100 cycles is 93%, which may benefit from the small volume change of the microporous carbon-sulfur cathode.

[0082] Comparative Example 2:

[0083] In this comparative example, a commercially available chemically sulfur-fixed SPAN cathode, i.e., a sulfurized polyacrylonitrile cathode, was used to form a sodium-sulfur battery with sodium metal. The sulfur content was 40%, and the electrolyte was the same as in Example 3, which was 1M NaPF 6 in EC / DEC = 1 / 1 vol% + 5% wt FEC.

[0084] By assembling the battery in the same way as in Example 3, as Figure 8 shown, since this sulfur cathode fixes sulfur in the form of chemical bonds, it is difficult to avoid the volume change of the sulfur in the cathode during charge and discharge. Therefore, the cycle stability is relatively poor, and the capacity retention rate after 100 cycles is 63%.

[0085] Example 4:

[0086] A microporous carbon cathode was prepared by mixing A / B / KOH in a mass ratio of 1 / 5 / 1, followed by ball milling, heat treatment, pickling, and drying, and then mixing the resulting mixture with sulfur in a mass ratio of 1 / 8. The sulfur content was 40%, and it was paired with a sodium metal anode to form a sodium-sulfur battery. The electrolyte was 1M NaPF 6 in EC / DEC = 1 / 1 vol% + 5% wt FEC.

[0087] Changing A / B from 1 / 10 to 1 / 5 will reduce the specific surface area of this microporous carbon material, but as Figure 9 shown, after assembling into a sodium-sulfur battery in the same way as in Example 3, it can also achieve relatively high cycle stability of the battery.

[0088] Example 5:

[0089] In this example, after mixing in a mass ratio of A / B / KOH = 1 / 10 / 1, the mixture is ball-milled, heat-treated, pickled and dried, and then the mixture is combined with SeS 2 to prepare a microporous carbon cathode by mixing in a mass ratio of 1 / 8. SeS 2 has a content of 40%, and is paired with a sodium metal anode to form a sodium-sulfur battery. The electrolyte is 1M NaPF 6 in EC / DEC = 1 / 1 vol% + 5% wt FEC.

[0090] The electrical conductivity of selenium is higher than that of sulfur. Introducing selenium into the cathode for doping is beneficial to improving the kinetics of the electrode. By assembling the sodium-sulfur battery in the manner of Example 3, as Figure 10 shown, this cathode also exhibits capacity in the ester-based electrolyte, indicating that the active material is confined in the micropores. As Figure 11 shown, the cycle stability of this cathode is also ensured.

[0091] Example 6:

[0092] In this example, after mixing in a mass ratio of A / B / KOH = 1 / 10 / 1, the mixture is ball-milled, heat-treated, pickled and dried, and then the mixture is combined with Se 5 S 3 to prepare a microporous carbon cathode by mixing in a mass ratio of 1 / 8. Se 5 S 3 has a content of 40%, and is paired with a sodium metal anode to form a sodium-sulfur battery. The electrolyte is 1M NaPF 6 in EC / DEC = 1 / 1 vol% + 5% wt FEC.

[0093] Different from Example 5 is that the relative contents of sulfur and selenium are changed. In this example, the selenium content exceeds that of sulfur. By assembling the battery in the manner of Example 3, as Figure 12 shown, since the capacity of selenium is lower than that of sulfur, the battery capacity decreases and is lower than that of Example 5, but it can still be exerted. Therefore, the sulfur-selenium compound is also confined in the micropores.

[0094] Example 7:

[0095] In this example, after mixing in a mass ratio of A / B / KOH = 1 / 10 / 1, it is combined with S 8 Se 1 Te 1 to prepare a microporous carbon cathode by mixing in a mass ratio of 1 / 8. S 8 Se 1 Te 1 has a content of 40%, and is paired with a sodium metal anode to form a sodium-sulfur battery. The electrolyte is 1M NaPF 6 in EC / DEC = 1 / 1 vol% + 5% wt FEC.

[0096] The electrical conductivity of tellurium is higher than that of selenium. Therefore, doping with tellurium is beneficial to further improve the kinetics. Sulfur, selenium and tellurium are doped in a molar ratio of 8 / 1 / 1 to prepare a microporous carbon cathode, and a sodium-sulfur battery is assembled in the manner of Example 3, as Figure 13 shown, the capacity can be exerted and is higher than that of Example 6. As Figure 14 shown, the stability of this cathode in ester-based electrolytes is also relatively high.

[0097] Those skilled in the art can easily understand that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a microporous carbon positive electrode material, characterized in that: include: The carbon source precursor, the solid salt and the alkali metal hydroxide are mixed and then ball milled; The ball-milled material is subjected to a primary heat treatment in an inert atmosphere; The material after the initial heat treatment is pickled and dried to obtain a microporous carbon material; The microporous carbon material is mixed with a positive electrode active material and subjected to a secondary heat treatment in an inert atmosphere to obtain a microporous carbon positive electrode material.

2. The method for preparing a microporous carbon positive electrode material according to claim 1, characterized in that: The carbon source precursor is a mixture of melamine and p-benzaldehyde, wherein the molar ratio of melamine to p-benzaldehyde is 10 / 1 to 1 / 100.

3. The method for preparing a microporous carbon positive electrode material according to claim 1, characterized in that: The solid salt is a mixture of LiCl and KCl, wherein the molar ratio of LiCl to KCl is 10 / 1 to 1 / 100.

4. The method for preparing a microporous carbon positive electrode material according to claim 1, characterized in that: The mass ratio of the carbon source precursor to the solid salt is 1 / 5 to 1 / 200; the mass ratio of the carbon source precursor to the alkali metal hydroxide is 100 / 1 to 1 / 100.

5. The method for preparing a microporous carbon positive electrode material according to claim 1, characterized in that: The ball-milled material is subjected to a primary heat treatment in an inert atmosphere, specifically, a heat treatment at a temperature of 100 to 1000° C. for 1 to 24 hours in an argon or nitrogen atmosphere.

6. The method for preparing a microporous carbon positive electrode material according to claim 1, characterized in that: The mass ratio of the microporous carbon material to the positive electrode active material is 1 / 0.1 to 1 / 10; The secondary heat treatment is specifically: heat treatment at a temperature of 200° C. to 500° C. for 2 to 8 hours in an argon or nitrogen atmosphere.

7. The method for preparing a microporous carbon positive electrode material according to claim 1, characterized in that: The positive electrode active material is a compound formed by one or more of sulfur, selenium, tellurium and iodine.

8. The method for preparing a microporous carbon positive electrode material according to claim 7, characterized in that: The positive electrode active material is selenium or a sulfur-selenium compound.

9. A microporous carbon positive electrode, characterized in that: It is prepared by the preparation method of the microporous carbon positive electrode material described in any one of claims 1 to 8.

10. A secondary battery, characterized in that: The microporous carbon positive electrode comprises the microporous carbon positive electrode as described in claim 9 above, and also comprises a negative electrode, wherein the material of the negative electrode is one or more of lithium metal, sodium metal, zinc metal, magnesium metal, aluminum metal, iron metal, lithium copper alloy, lithium aluminum alloy, lithium silicon alloy, lithium silver alloy, graphite, hard carbon, silicon and silicon carbon.

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