A porous hard carbon negative electrode material and its preparation method and sodium ion battery

Abstract

The present invention provides a porous hard carbon negative electrode material and its preparation method and sodium ion battery, relating to the technical field of sodium ion batteries; the preparation method comprises the following steps: a template, a hard carbon precursor, an activator and 1-ethyl-3-methylimidazole hydrogen sulfate are evenly ground to obtain a mixture; the mixture is heated to 700-900°C in an inert gas atmosphere to obtain a carbonized material; the carbonized material is subjected to secondary pore formation to obtain a porous carbonized material; the porous carbonized material is washed and dried, and then immersed in a polyoxometalate sodium salt solution to obtain a soaked material; the soaked material is washed and dried, and the dried material is heated to 1200-1400°C in an inert gas atmosphere to obtain a porous hard carbon negative electrode material. The present invention introduces active sites into the porous carbon material during the carbonization process, and then introduces polyoxometalate sodium salt on the active sites. The polyoxometalate skeleton in the polyoxometalate sodium salt can allow sodium ions to be transmitted in its micropores, thereby improving the gram capacity and coulombic efficiency of the material.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion batteries, and in particular to a porous hard carbon negative electrode material and a preparation method thereof, and a sodium ion battery. Background Art

[0002] Sodium-ion batteries came into being when the price of lithium carbonate remained high. Currently, many battery manufacturers have released sodium-ion battery products, but the sodium-ion battery supply chain is still immature. The main reason is that the material end is still in the development stage and not many can be mass-produced.

[0003] Among them, the most representative is the negative electrode material of sodium ion battery; because the hard carbon negative electrode material has a larger interlayer spacing, it is more suitable for sodium ions with a larger radius to be embedded and deintercalated therein. Therefore, the current negative electrode material of sodium ion battery is mainly hard carbon negative electrode material.

[0004] In the past two years, with the progress of research, porous carbon materials have emerged as negative electrode materials for sodium-ion batteries. Porous carbon materials create pores on carbon materials and use rich pore structures to promote the adsorption and storage of sodium ions, thereby increasing the capacity of negative electrode materials.

[0005] At present, the preparation method of porous carbon is generally to first carbonize the precursor at a certain temperature, clean out the impurities, and then introduce water vapor or air at a certain temperature for activation and secondary pore formation. Although the porous carbon prepared by this method improves the capacity of the negative electrode material to a certain extent, the pore structure produced by the secondary pore formation has inconsistent pore sizes. Among them, the pore structure with a smaller pore size increases the surface area of ​​the material, but because it is difficult for sodium ions to freely intercalate and deintercalate therein, this part of the pore structure not only cannot be effectively utilized, but also leads to a lower gram capacity of the negative electrode material. Summary of the Invention

[0006] The technical problem to be solved by the present invention is: in order to solve the problem of low gram capacity of porous hard carbon negative electrode materials in the prior art, the present invention provides a method for preparing porous hard carbon negative electrode materials. The preparation method introduces NS atoms into the porous hard carbon negative electrode material to form active sites, so that sodium ions are captured by more active sites, which helps to increase the gram capacity of the negative electrode material and solves the problem of low gram capacity of porous hard carbon negative electrode materials in the prior art.

[0007] The technical solution adopted by the present invention to solve its technical problem is:

[0008] A method for preparing a porous hard carbon negative electrode material comprises the following steps:

[0009] S1: Grinding the template, hard carbon precursor, activator and 1-ethyl-3-methylimidazolium hydrogen sulfate to obtain a mixture;

[0010] S2: heating the mixture to 700-900° C. in an inert gas atmosphere for carbonization to obtain a carbonized material;

[0011] S3: performing secondary pore formation on the carbonized material to obtain a porous carbonized material;

[0012] S4: washing and drying the porous carbonized material, and then soaking it in a sodium salt solution of polyoxometalate to obtain a soaked material;

[0013] S5: washing and drying the soaked material to obtain a dried material;

[0014] S6: heating the dried material to 1200-1400° C. in an inert gas atmosphere to obtain a porous hard carbon negative electrode material.

[0015] Optionally, the template is selected from at least one of potassium chloride and zinc chloride.

[0016] Optionally, the template is a mixture of potassium chloride and zinc chloride in a mass ratio of (3-7):7.

[0017] Optionally, the hard carbon precursor is selected from at least one of bamboo, coconut shell, starch, rice husk, walnut shell, anthracite, asphalt, and phenolic resin.

[0018] Optionally, the starch is selected from at least one of potato starch, corn starch, wheat starch, tapioca starch, pea starch, and sweet potato starch.

[0019] Optionally, the activator is sodium hydroxide.

[0020] Optionally, the sodium salt of polyoxometalate is selected from Na3XY 12 O 40 、Na4XY 12 O 40 At least one of; wherein X is selected from any one of P and Si; Y is selected from any one of Mo and W.

[0021] Optionally, in step S1 , the mass ratio of the template, the hard carbon precursor, the activator and 1-ethyl-3-methylimidazole hydrogen sulfate is (0.5-1.5):(5-8):(1-5):0.1.

[0022] Another object of the present invention is to provide a porous hard carbon negative electrode material, which is prepared by the method for preparing the porous hard carbon negative electrode material as described above.

[0023] Another object of the present invention is to provide a sodium ion battery comprising the porous hard carbon negative electrode material as described above.

[0024] The beneficial effects of the present invention are:

[0025] The preparation method of the porous hard carbon negative electrode material provided by the present invention introduces active sites into the porous carbon material by co-doping with NS during the carbonization process, and then introduces sodium polyoxometalate salts on the active sites with the help of the active sites formed by NS. The polyoxometalate skeleton in the sodium polyoxometalate salt can allow sodium ions to be transported in its micropores, which has a certain sodium supplementation effect on the hard carbon negative electrode material, thereby improving the gram capacity and coulombic efficiency of the material. DETAILED DESCRIPTION

[0026] The present invention will now be described in further detail. The embodiments described below are exemplary and intended to explain the present invention, but should not be construed as limiting the present invention. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort are intended to fall within the scope of protection of the present invention.

[0027] In order to solve the problem of low specific capacity of porous hard carbon negative electrode materials in the prior art, the present invention provides a method for preparing a porous hard carbon negative electrode material, which comprises the following steps:

[0028] S1: Grinding the template, hard carbon precursor, activator and 1-ethyl-3-methylimidazolium hydrogen sulfate to obtain a mixture;

[0029] S2: heating the mixture to 700-900° C. in an inert gas atmosphere for carbonization to obtain a carbonized material;

[0030] In this step, under high temperature conditions, the template agent quickly melts and evaporates to form a large number of pores; at the same time, the activator reacts with the carbon in the hard carbon precursor to generate a large amount of volatile gas, which further forms more pore structures through the volatile gas, and at the same time, the pores generated by the evaporation of the template agent are further enlarged, which helps to increase the pore diameter of the pores in the negative electrode material, increase the number of large-pore pores, and reduce the number of invalid micropores, thereby facilitating the transmission of sodium ions during the cycle, increasing the gram capacity of the negative electrode material, and improving its coulombic efficiency; and because 1-ethyl-3-methylimidazole hydrogen sulfate is uniformly mixed in the mixture, the 1-ethyl-3-methylimidazole sulfur The acid hydrogen salt serves as both a nitrogen source and a sulfur source, and can obtain a NS co-doped carbonized material. Since NS atoms have abundant active sites, they can enhance the polarity of the carbon material. When it is used as a negative electrode material, sodium ions will be captured by more active sites, which is more conducive to improving the gram capacity of the negative electrode material. In addition, since the present invention first mixes 1-ethyl-3-methylimidazole hydrogen sulfate with a template, a hard carbon precursor, and an activator before carbonizing, it is also helpful to introduce nitrogen atoms and sulfur atoms into the generated pores in situ during the pore generation process, thereby increasing the active sites in the pores, helping to promote the transmission of sodium ions in the pores, and improving the gram capacity and coulombic efficiency of the negative electrode material.

[0031] S3: Performing secondary pore formation on the carbonized material to obtain a porous carbonized material;

[0032] The pore structure on the negative electrode material is further increased by secondary pore formation. The present invention preferably includes placing the carbonized material in a rotary kiln after ultrasonic cleaning, impurity removal, and drying, and then activating and secondary pore formation while passing water vapor. This step can also be performed by other existing technologies for secondary pore formation, and the present invention does not specifically limit this step.

[0033] S4: washing and drying the porous carbonized material, and then soaking it in a sodium salt solution of polyoxometalate to obtain a soaked material;

[0034] Preferably, the porous carbonized material is washed 10 times with hydrochloric acid and deionized water, dried at 80° C., and then immersed in a 1M sodium polyoxometalate solution for 5-8 hours to obtain an immersed material;

[0035] Because micropores with smaller pore sizes are inevitably generated during carbonization and secondary pore formation, if these micropores are not treated, it is difficult for sodium ions to freely intercalate and deintercalate during the cycle, resulting in the inability to effectively utilize these micropores. Based on this, the present invention introduces sodium polyoxometalate salts into the negative electrode material by immersing the porous carbonized material in a sodium polyoxometalate solution, which can achieve a certain sodium supplementation effect, thereby helping to improve the coulombic efficiency of the negative electrode material. In addition, since the present invention introduces 1-ethyl-3-methylimidazole hydrogen sulfate into the negative electrode material, especially the negative electrode material NS atoms are introduced into the pore structure of the porous carbonized material. Therefore, after immersing the porous carbonized material in a sodium polyoxometalate solution, the active sites formed by NS can be used to introduce sodium polyoxometalate at the active sites, thereby introducing sodium polyoxometalate into the microporous structure that is originally not conducive to the transport of sodium ions. The polyoxometalate skeleton in the sodium polyoxometalate allows sodium ions to be transported in its micropores, so that these micropores can be effectively utilized, thereby improving the utilization rate of the micropores. For hard carbon negative electrode materials, it has a certain sodium supplementation effect, thereby improving the gram capacity and coulombic efficiency of the material.

[0036] S5: washing and drying the soaked material to obtain a dried material;

[0037] Preferably, in this step, the excess sodium polyoxometalate salt is washed with deionized water, and the obtained solid is filtered and dried to obtain a dried material;

[0038] S6: heating the dried material to 1200-1400° C. in an inert gas atmosphere to obtain a porous hard carbon negative electrode material.

[0039] The preparation method of the porous hard carbon negative electrode material provided by the present invention introduces active sites into the porous carbon material by co-doping with NS during the carbonization process, and then introduces sodium polyoxometalate salts on the active sites with the help of the active sites formed by NS. The polyoxometalate skeleton in the sodium polyoxometalate salt can allow sodium ions to be transported in its micropores, which has a certain sodium supplementation effect on the hard carbon negative electrode material, thereby improving the gram capacity and coulombic efficiency of the material.

[0040] The porous hard carbon negative electrode material prepared by the present invention has a rich pore structure, and the micropores with smaller pore sizes are also effectively utilized.

[0041] In the present invention, the template is preferably selected from at least one of potassium chloride and zinc chloride, and further preferably the template is a mixture of potassium chloride and zinc chloride in a mass ratio of (3-7):7.

[0042] The present invention uses at least one of potassium chloride and zinc chloride as a template, which can quickly melt and evaporate during the high-temperature carbonization process in step S2, thereby being able to serve as a self-sacrificial template to form a rich pore structure in the carbon material.

[0043] The preferred activator of the present invention is sodium hydroxide, so that it can react with the carbon material during the high-temperature carbonization process in step S2 to generate volatile gas. The volatile gas can increase the number of pore structures on the one hand, and combine with the template agent on the other hand to increase the pore size of the pore structure, increase the number of large-pore structures, and reduce the number of invalid micropores.

[0044] The hard carbon precursor of the present invention is preferably selected from at least one of bamboo, coconut shell, starch, rice husk, walnut shell, anthracite, asphalt, and phenolic resin; further preferably, the starch is selected from at least one of potato starch, corn starch, wheat starch, cassava starch, pea starch, and sweet potato starch.

[0045] It should be noted that when starch is selected as the hard carbon precursor, step S2 further includes heating the mixture to 160-300° C. in an inert gas atmosphere before carbonization to remove starch precursor tar.

[0046] The preferred sodium salt of polyoxometalate of the present invention is selected from Na3XY 12 O 40 、Na4XY 12 O 40 At least one of; wherein X is selected from any one of P and Si; Y is selected from any one of Mo and W.

[0047] In order to take into account the performance and economy of the porous hard carbon negative electrode material, the mass ratio of the template, hard carbon precursor, activator and 1-ethyl-3-methylimidazole hydrogen sulfate in step S1 of the present invention is preferably (0.5-1.5): (5-8): (1-5): 0.1.

[0048] The present invention provides a method for preparing a porous hard carbon negative electrode material. The prepared porous hard carbon negative electrode material has a rich pore structure, which is conducive to the embedding and extraction of sodium ions. The introduced NS atoms have abundant active sites and can enhance the polarity of the carbon material. When it is used as a negative electrode material, sodium ions will be captured by more active sites, which is more conducive to improving the gram capacity. With the help of the active sites formed by NS, sodium polyoxometalate salts are introduced on the active sites. The polyoxometalate skeleton in the sodium polyoxometalate salt can allow sodium ions to be transmitted in its micropores, which has a certain sodium supplementation effect on the hard carbon negative electrode material, thereby improving the coulombic efficiency of the material.

[0049] Another object of the present invention is to provide a porous hard carbon negative electrode material, which is prepared by the method for preparing the porous hard carbon negative electrode material as described above.

[0050] The porous hard carbon negative electrode material provided by the present invention introduces active sites into the porous carbon material by co-doping with NS during the carbonization process, and then introduces sodium polyoxometalate salts on the active sites with the help of the active sites formed by NS. The polyoxometalate skeleton in the sodium polyoxometalate salt can allow sodium ions to be transported in its micropores, which has a certain sodium supplementation effect on the hard carbon negative electrode material, thereby improving the gram capacity and coulombic efficiency of the material.

[0051] Another object of the present invention is to provide a sodium ion battery, which includes the porous hard carbon negative electrode material as described above.

[0052] The sodium ion battery provided by the present invention adopts the above-mentioned porous hard carbon negative electrode material, introduces active sites into the porous carbon material by co-doping with NS during the carbonization process, and then introduces polyoxometalate sodium salt on the active sites with the help of the active sites formed by NS. The polyoxometalate skeleton in the polyoxometalate sodium salt allows sodium ions to be transported in its micropores, which has a certain sodium supplementation effect on the hard carbon negative electrode material, thereby improving the gram capacity and coulombic efficiency of the material.

[0053] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, specific embodiments of the present invention are described in detail below.

[0054] Example 1

[0055] This embodiment provides a method for preparing a porous hard carbon negative electrode material, which comprises the following steps:

[0056] S1: Grind potassium chloride and zinc chloride in a mass ratio of 5:7 to obtain a template;

[0057] The template, potato starch, sodium hydroxide and 1-ethyl-3-methylimidazole hydrogen sulfate in a mass ratio of 1:6:3:0.1 were ground uniformly to obtain a mixture;

[0058] S2: placing the mixture in a rotary kiln, heating it to 250°C in a nitrogen atmosphere, keeping it warm for 6 hours, and removing the tar; heating the treated mixture to 800°C, keeping it warm for 4 hours, and carbonizing it to obtain a carbonized material;

[0059] S3: After ultrasonic cleaning, impurity removal, and drying, the carbonized material is placed in a rotary kiln again, and activated and secondary pore-forming is performed while passing water vapor to obtain a porous carbonized material;

[0060] S4: The prepared porous carbonized material was washed with hydrochloric acid and deionized water 10 times each, dried at 80 °C, and poured into 1M Na3PW 12 O 40Soaking in the solution for 5 hours to obtain a soaking material;

[0061] S5: Wash off excess Na3PW with deionized water 12 O 40 The obtained solid is filtered and dried to obtain a dried material;

[0062] S6: The dried material was placed in a tube furnace, heated to 1300° C. in a nitrogen atmosphere, and kept at this temperature for 5 h to obtain a porous hard carbon negative electrode material.

[0063] Example 2

[0064] This embodiment provides a method for preparing a porous hard carbon negative electrode material, which comprises the following steps:

[0065] S1: Grind potassium chloride and zinc chloride in a mass ratio of 5:7 to obtain a template;

[0066] Grind the template, rice husk, sodium hydroxide, and 1-ethyl-3-methylimidazole hydrogen sulfate in a mass ratio of 0.5:6:4:0.1 to obtain a mixture;

[0067] S2: placing the mixture in a rotary kiln, heating it to 700°C in a nitrogen atmosphere, and keeping it at that temperature for 6 hours to carbonize it to obtain a carbonized material;

[0068] S3: After ultrasonic cleaning, impurity removal, and drying, the carbonized material is placed in a rotary kiln again, and activated and secondary pore-forming is performed while passing water vapor to obtain a porous carbonized material;

[0069] S4: The prepared porous carbonized material was washed with hydrochloric acid and deionized water 10 times each, dried at 80 ° C, and poured into a 1M Na3PMo 12 O 40 Soaking in the solution for 5 hours to obtain a soaking material;

[0070] S5: Wash off excess Na3PMo with deionized water 12 O 40 The obtained solid is filtered and dried to obtain a dried material;

[0071] S6: The dried material was placed in a tube furnace, heated to 1200° C. in a nitrogen atmosphere, and kept at this temperature for 5 h to obtain a porous hard carbon negative electrode material.

[0072] Example 3

[0073] This embodiment provides a method for preparing a porous hard carbon negative electrode material, which comprises the following steps:

[0074] S1: Grind potassium chloride and zinc chloride in a mass ratio of 5:7 to obtain a template;

[0075] The template, wheat starch, sodium hydroxide and 1-ethyl-3-methylimidazole hydrogen sulfate in a mass ratio of 1.5:6:1:0.1 were ground uniformly to obtain a mixture;

[0076] S2: placing the mixture in a rotary kiln, heating it to 250°C in a nitrogen atmosphere, keeping it warm for 6 hours, and removing the tar; heating the treated mixture to 900°C, keeping it warm for 4 hours, and carbonizing it to obtain a carbonized material;

[0077] S3: After ultrasonic cleaning, impurity removal, and drying, the carbonized material is placed in a rotary kiln again, and activated and secondary pore-forming is performed while passing water vapor to obtain a porous carbonized material;

[0078] S4: The prepared porous carbonized material was washed with hydrochloric acid and deionized water 10 times each, dried at 80 ° C, and poured into 1M Na4SiMo 12 O 40 Soaking in the solution for 5 hours to obtain a soaking material;

[0079] S5: Wash off excess Na4SiMo with deionized water 12 O 40 The obtained solid is filtered and dried to obtain a dried material;

[0080] S6: The dried material was placed in a tube furnace, heated to 1400° C. in a nitrogen atmosphere, and kept at this temperature for 5 h to obtain a porous hard carbon negative electrode material.

[0081] Example 4

[0082] This embodiment provides a method for preparing a porous hard carbon negative electrode material, which comprises the following steps:

[0083] S1: Grind potassium chloride, potato starch, sodium hydroxide, and 1-ethyl-3-methylimidazole hydrogen sulfate in a mass ratio of 1:6:3:0.1 to obtain a mixture;

[0084] S2: placing the mixture in a rotary kiln, heating it to 250°C in a nitrogen atmosphere, keeping it warm for 6 hours, and removing the tar; heating the treated mixture to 800°C, keeping it warm for 4 hours, and carbonizing it to obtain a carbonized material;

[0085] S3: After ultrasonic cleaning, impurity removal, and drying, the carbonized material is placed in a rotary kiln again, and activated and secondary pore-forming is performed while passing water vapor to obtain a porous carbonized material;

[0086] S4: The prepared porous carbonized material was washed with hydrochloric acid and deionized water 10 times each, dried at 80 °C, and poured into 1M Na3PW 12 O 40 Soaking in the solution for 5 hours to obtain a soaking material;

[0087] S5: Wash off excess Na3PW with deionized water 12 O 40 The obtained solid is filtered and dried to obtain a dried material;

[0088] S6: The dried material was placed in a tube furnace, heated to 1300° C. in a nitrogen atmosphere, and kept at this temperature for 5 h to obtain a porous hard carbon negative electrode material.

[0089] Example 5

[0090] This embodiment provides a method for preparing a porous hard carbon negative electrode material, which comprises the following steps:

[0091] S1: Grind zinc chloride, corn starch, sodium hydroxide, and 1-ethyl-3-methylimidazolium hydrogen sulfate in a mass ratio of 1:6:3:0.1 to obtain a mixture;

[0092] S2: placing the mixture in a rotary kiln, heating it to 250°C in a nitrogen atmosphere, keeping it warm for 6 hours, and removing the tar; heating the treated mixture to 800°C, keeping it warm for 4 hours, and carbonizing it to obtain a carbonized material;

[0093] S3: After ultrasonic cleaning, impurity removal, and drying, the carbonized material is placed in a rotary kiln again, and activated and secondary pore-forming is performed while passing water vapor to obtain a porous carbonized material;

[0094] S4: The prepared porous carbonized material was washed with hydrochloric acid and deionized water 10 times each, dried at 80 °C, and poured into 1M Na3PW 12 O 40 Soaking in the solution for 5 hours to obtain a soaking material;

[0095] S5: Wash off excess Na3PW with deionized water 12 O 40 The obtained solid is filtered and dried to obtain a dried material;

[0096] S6: The dried material was placed in a tube furnace, heated to 1300° C. in a nitrogen atmosphere, and kept at this temperature for 5 h to obtain a porous hard carbon negative electrode material.

[0097] Comparative Example 1

[0098] This comparative example provides a method for preparing a negative electrode material, which comprises the following steps:

[0099] S1: placing potato starch in a rotary kiln, heating it to 250°C in a nitrogen atmosphere, keeping it warm for 6 hours, and removing tar; heating the treated potato starch to 800°C, keeping it warm for 4 hours, and carbonizing it to obtain a carbonized material;

[0100] S2: After ultrasonic cleaning, impurity removal, and drying, the carbonized material is placed in a rotary kiln again and activated and pore-forming while passing water vapor to obtain a porous carbonized material;

[0101] S3: washing the prepared porous carbonized material with deionized water 10 times and drying it at 80° C. to obtain a dried material;

[0102] S4: The dried material was placed in a tube furnace, heated to 1300° C. in a nitrogen atmosphere, and kept warm for 5 h to obtain the negative electrode material.

[0103] Comparative Example 2

[0104] This comparative example provides a method for preparing a negative electrode material, which comprises the following steps:

[0105] S1: Grind potassium chloride and zinc chloride in a mass ratio of 5:7 to obtain a template;

[0106] The template, potato starch and sodium hydroxide in a mass ratio of 1:6:3 were ground evenly to obtain a mixture;

[0107] S2: placing the mixture in a rotary kiln, heating it to 250°C in a nitrogen atmosphere, keeping it warm for 6 hours, and removing the tar; heating the treated mixture to 800°C, keeping it warm for 4 hours, and carbonizing it to obtain a carbonized material;

[0108] S3: After ultrasonic cleaning, impurity removal, and drying, the carbonized material is placed in a rotary kiln again, and activated and secondary pore-forming is performed while passing water vapor to obtain a porous carbonized material;

[0109] S4: The prepared porous carbonized material was washed with hydrochloric acid and deionized water 10 times each, dried at 80 °C, and poured into 1M Na3PW 12 O 40 Soaking in the solution for 5 hours to obtain a soaking material;

[0110] S5: Wash off excess Na3PW with deionized water 12 O 40 The obtained solid is filtered and dried to obtain a dried material;

[0111] S6: Place the dried material in a tube furnace, heat it to 1300° C. in a nitrogen atmosphere, and keep it warm for 5 hours to obtain the negative electrode material.

[0112] Comparative Example 3

[0113] This comparative example provides a method for preparing a negative electrode material, which comprises the following steps:

[0114] S1: Grind potassium chloride and zinc chloride in a mass ratio of 5:7 to obtain a template;

[0115] The template, potato starch, sodium hydroxide and 1-ethyl-3-methylimidazole hydrogen sulfate in a mass ratio of 1:6:3:0.1 were ground uniformly to obtain a mixture;

[0116] S2: placing the mixture in a rotary kiln, heating it to 250°C in a nitrogen atmosphere, keeping it warm for 6 hours, and removing the tar; heating the treated mixture to 800°C, keeping it warm for 4 hours, and carbonizing it to obtain a carbonized material;

[0117] S3: After ultrasonic cleaning, impurity removal, and drying, the carbonized material is placed in a rotary kiln again, and activated and secondary pore-forming is performed while passing water vapor to obtain a porous carbonized material;

[0118] S4: washing the prepared porous carbonized material with hydrochloric acid and deionized water 10 times each, and drying at 80° C. to obtain a dried material;

[0119] S5: The dried material was placed in a tube furnace, heated to 1300° C. in a nitrogen atmosphere, and kept at this temperature for 5 h to obtain the negative electrode material.

[0120] Comparative Example 4

[0121] This comparative example provides a method for preparing a negative electrode material, which comprises the following steps:

[0122] S1: Grind potassium chloride and zinc chloride in a mass ratio of 5:7 to obtain a template;

[0123] The template agent, potato starch and 1-ethyl-3-methylimidazole hydrogen sulfate in a mass ratio of 1:6:0.1 were ground uniformly to obtain a mixture;

[0124] S2: placing the mixture in a rotary kiln, heating it to 250°C in a nitrogen atmosphere, keeping it warm for 6 hours, and removing the tar; heating the treated mixture to 800°C, keeping it warm for 4 hours, and carbonizing it to obtain a carbonized material;

[0125] S3: After ultrasonic cleaning, impurity removal, and drying, the carbonized material is placed in a rotary kiln again, and activated and secondary pore-forming is performed while passing water vapor to obtain a porous carbonized material;

[0126] S4: The prepared porous carbonized material was washed with hydrochloric acid and deionized water 10 times each, dried at 80 °C, and poured into 1M Na3PW 12 O 40 Soaking in the solution for 5 hours to obtain a soaking material;

[0127] S5: Wash off excess Na3PW with deionized water 12 O 40 The obtained solid is filtered and dried to obtain a dried material;

[0128] S6: Place the dried material in a tube furnace, heat it to 1300° C. in a nitrogen atmosphere, and keep it warm for 5 hours to obtain the negative electrode material.

[0129] Comparative Example 5

[0130] This comparative example provides a method for preparing a negative electrode material, which comprises the following steps:

[0131] S1: Grind potato starch, sodium hydroxide, and 1-ethyl-3-methylimidazolium hydrogen sulfate in a mass ratio of 6:3:0.1 to obtain a mixture;

[0132] S2: placing the mixture in a rotary kiln, heating it to 250°C in a nitrogen atmosphere, keeping it warm for 6 hours, and removing the tar; heating the treated mixture to 800°C, keeping it warm for 4 hours, and carbonizing it to obtain a carbonized material;

[0133] S3: After ultrasonic cleaning, impurity removal, and drying, the carbonized material is placed in a rotary kiln again, and activated and secondary pore-forming is performed while passing water vapor to obtain a porous carbonized material;

[0134] S4: The prepared porous carbonized material was washed with hydrochloric acid and deionized water 10 times each, dried at 80 °C, and poured into 1M Na3PW 12 O 40 Soaking in the solution for 5 hours to obtain a soaking material;

[0135] S5: Wash off excess Na3PW with deionized water 12 O 40 The obtained solid is filtered and dried to obtain a dried material;

[0136] S6: Place the dried material in a tube furnace, heat it to 1300° C. in a nitrogen atmosphere, and keep it warm for 5 hours to obtain the negative electrode material.

[0137] The negative electrode materials prepared in the above embodiments and comparative examples were used as negative electrode active materials, mixed evenly with vinylidene fluoride (PVDF) (dissolved in N-methylpyrrolidone) and conductive carbon black in a mass ratio of 90:5:5, coated into electrode films, dried in a vacuum drying oven at 120°C for 12 hours, and rolled and punched to obtain hard carbon negative electrode sheets. A metal sodium sheet was used as the counter electrode, 1 mol / L NaPF6 (EC-DEC = 1:1) was used as the electrolyte, and the obtained hard carbon negative electrode sheets were assembled into 2430 button-type batteries in a glove box to test their electrochemical properties. The test voltage was (0-3) V and the current was 0.1C. The test results are shown in Table 1:

[0138] Table 1

[0139]

[0140] From the above data, it can be seen that the negative electrode materials prepared in each embodiment have high gram capacity and coulombic efficiency; Comparative Example 1 is pure hard carbon prepared by traditional methods, and its gram capacity and coulombic efficiency are the lowest; Comparative Example 2, compared with Example 1, has no NS heteroatom, which is equivalent to the lack of active sites. Although it is immersed in sodium polyoxometalate, the sodium polyoxometalate introduced into the microporous structure is reduced, and not only the gram capacity is significantly reduced, but the coulombic efficiency is also reduced; Comparative Example 3 contains heteroatoms but no sodium polyoxometalate, and its gram capacity is slightly reduced. , but its coulombic efficiency drops significantly, because the sodium polyoxometalate salt plays the role of sodium supplementation, and without sodium supplementation materials, the coulombic efficiency is greatly affected; Compared with Example 1, in Comparative Example 4, no activator is added in step S1, and the number of pores in the prepared negative electrode material is relatively small, and the number of microporous structures with smaller pore sizes is relatively large, so its sodium holding capacity is poor and its gram capacity is relatively small; Compared with Example 1, in Comparative Example 5, no template is added in step S1, and the number of pores in the prepared negative electrode material is relatively small, and the number of microporous structures with smaller pore sizes is relatively large, which also affects its gram capacity.

[0141] With the above-described preferred embodiments of the present invention as a guide, and with reference to the above description, relevant personnel are fully capable of making various changes and modifications without departing from the technical scope of this invention. The technical scope of this invention is not limited to the contents of the specification and must be determined according to the scope of the claims.

Claims

1. A method for preparing a porous hard carbon negative electrode material, characterized in that: The steps include: S1: Grinding the template, hard carbon precursor, activator and 1-ethyl-3-methylimidazolium hydrogen sulfate to obtain a mixture; S2: heating the mixture to 700-900° C. in an inert gas atmosphere for carbonization to obtain a carbonized material; S3: performing secondary pore formation on the carbonized material to obtain a porous carbonized material; S4: washing and drying the porous carbonized material, and then soaking it in a sodium salt solution of polyoxometalate to obtain a soaked material; S5: washing and drying the soaked material to obtain a dried material; S6: heating the dried material to 1200-1400° C. in an inert gas atmosphere to obtain a porous hard carbon negative electrode material; The sodium salt of polyoxometalate is selected from Na3XY 12 O 40 、Na4XY 12 O 40 At least one of; wherein X is selected from any one of P and Si; Y is selected from any one of Mo and W.

2. The method for preparing a porous hard carbon negative electrode material according to claim 1, wherein: The template is selected from at least one of potassium chloride and zinc chloride.

3. The method for preparing a porous hard carbon negative electrode material according to claim 2, wherein: The template is a mixture of potassium chloride and zinc chloride in a mass ratio of (3-7):

7.

4. The method for preparing a porous hard carbon negative electrode material according to claim 1, wherein: The hard carbon precursor is selected from at least one of bamboo, coconut shell, starch, rice husk, walnut shell, anthracite, asphalt and phenolic resin.

5. The method for preparing a porous hard carbon negative electrode material according to claim 4, wherein: The starch is selected from at least one of potato starch, corn starch, wheat starch, tapioca starch, pea starch and sweet potato starch.

6. The method for preparing a porous hard carbon negative electrode material according to claim 1, wherein: The activator is sodium hydroxide.

7. The method for preparing a porous hard carbon negative electrode material according to any one of claims 1 to 6, wherein: In step S1, the mass ratio of the template, the hard carbon precursor, the activator and 1-ethyl-3-methylimidazole hydrogen sulfate is (0.5-1.5): (5-8): (1-5): 0.

1.

8. A porous hard carbon negative electrode material, characterized in that: The porous hard carbon negative electrode material is prepared by the preparation method according to any one of claims 1 to 7.

9. A sodium ion battery, characterized in that: Comprising the porous hard carbon negative electrode material as claimed in claim 8.

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