Heterojunction hard carbon material, sodium ion battery negative electrode material and preparation method and application

Abstract

The application discloses a heterojunction hard carbon material, a sodium ion battery negative electrode material and a preparation method and application; the application uses cheap and easily obtained reed and lignite as raw materials, the reed is subjected to low-temperature pre-carbonization treatment, the lignite is subjected to acid washing pretreatment, a precursor suitable for swelling treatment is formed, then swelling treatment is carried out, the closed pore structure of the carbon material is realized, then plasma ball milling treatment is carried out, carbon coating is realized, then high-temperature hard carbonization treatment is carried out, the carbon layer rearrangement is realized, the pore structure of the hard carbon material is regulated and controlled, and rich closed pore structures are obtained. The hard carbon material has a heterojunction hard carbon coating structure inside, and can be applied to a sodium ion battery; the sodium ion battery negative electrode material uses the above-mentioned heterojunction hard carbon material, the first coulomb efficiency and the cycle stability are improved, the electrochemical performance of the sodium ion battery is improved, the preparation cost of the hard carbon material is effectively reduced, and the hard carbon material is suitable for industrialized production.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery materials, and particularly relates to a heterojunction hard carbon material, a sodium ion battery negative electrode material and a preparation method and application. BACKGROUND

[0002] With the gradual depletion of fossil energy and the continuous development of energy technology, the charging battery dominated by lithium ion batteries, with its excellent electrochemical performance, has become the most suitable technical means for portable energy storage. However, the resource amount of lithium element is small and unevenly distributed, which greatly limits the development of its large-scale application. Based on this, the research and development of charging batteries have gradually shifted to other metal ion batteries. Due to the similar electrochemical principles, and the abundant reserves and low cost of sodium element, sodium ion batteries have received widespread attention in recent years. Graphite has a narrow interlayer spacing and cannot form stable sodium intercalation compounds with sodium, resulting in poor sodium storage performance. Hard carbon has good comprehensive performance, and the precursor source is widely available and the production cost is low, so it is a good negative electrode material for sodium ion batteries. Hard carbon has a wide interlayer spacing and additional sodium storage sites, and has high specific capacity and good cycle stability, but the structure is complex, resulting in poor rate performance.

[0003] At present, the common precursors of hard carbon are high molecular polymers such as resin, cellulose, starch, sucrose, etc., as well as various nut shells, plant biomass raw materials, and petroleum chemical by-products and coal-based materials. There are the following shortcomings: 1. High molecular precursors are mainly chemical products extracted from biomass, including glucose, sucrose, starch, cellulose, and lignin, etc. However, they have poor electrical conductivity and are not conducive to the transmission of electrons, which is not suitable for the preparation of hard carbon materials; 2. Petroleum chemical by-products and coal-based materials mainly include coal, pitch, petroleum coke, etc., which have the advantages of low cost and high carbon yield. However, graphitization is easy to occur during high-temperature carbonization, which forms a highly ordered carbon layer structure and is not conducive to sodium ion storage. The above shortcomings result in high raw material prices and low carbon yield in the preparation of existing hard carbon materials. Compared with the above, biomass precursors are mainly agricultural and forestry plant waste such as lotus leaves, peanut shells, and pomelo peels. Using them as raw materials to prepare hard carbon materials can greatly reduce the cost.

[0004] However, during the pyrolysis process of preparing biomass carbon materials, carbon atoms are prone to agglomeration, and the active sites of the material are reduced. At present, coal-based hard carbon has the disadvantage of high raw material price, and biomass hard carbon has the disadvantages of large irreversible capacity and low first efficiency, which greatly limits its application in energy storage.

[0005] Therefore, it is urgent to provide a technology to overcome the shortcomings of biomass and coal-based materials, to prepare hard carbon materials by this technology, and to use them as negative electrode materials for sodium ion batteries to improve the electrochemical performance of the battery and increase the cost advantage of sodium ion batteries. SUMMARY

[0006] In view of the deficiencies and shortcomings of the prior art, the present application aims to provide a heterojunction hard carbon material, a sodium-ion battery negative electrode material, a preparation method and an application, by providing a mixed heterojunction hard carbon material and a preparation method thereof, using such a hard carbon material as a raw material to prepare a negative electrode sheet, and applying the negative electrode sheet in a sodium-ion battery, so as to reduce the cost of preparing a hard carbon material from a biomass precursor, improve the electrochemical performance of the sodium-ion battery, and increase the cost advantage of the sodium-ion battery.

[0007] To achieve the above technical purposes, the technical scheme of the present application is as follows:

[0008] The preparation method of the heterojunction hard carbon material comprises the following steps:

[0009] S1: The reed is washed multiple times with deionized water, air-dried, and then broken down to obtain reed yellow powder; the reed yellow powder is pretreated to obtain reed pre-carbonization powder; lignite is mechanically ball milled and sieved to obtain lignite black powder of a certain particle size, which is then acid-washed and pretreated to obtain lignite pre-ash removal powder;

[0010] S2: The reed pre-carbonization powder and the lignite pre-ash removal powder are sequentially subjected to mechanical ball milling and sieving to obtain intermediate reed carbon material and intermediate lignite material, respectively;

[0011] S3: The intermediate reed carbon material and the intermediate lignite material are sequentially mixed and ground, swelled, washed with deionized water, and dried to obtain mixed black powder; the mixed black powder is added to a plasma ball mill, and anhydrous ethanol is added for plasma ball milling and coating treatment to obtain carbonized precursor powder;

[0012] S4: The carbonized precursor powder is subjected to high-temperature carbonization treatment, and then ground and sieved to obtain the heterojunction hard carbon material.

[0013] Preferably, the number of times of deionized water washing in S1 is 3-6 times; the drying temperature is 50-180 DEG C; the drying time is 5-20 h; and the breaking time is 20 min-50 min;

[0014] Preferably, the atmosphere condition for pretreating the reed yellow powder in S1 is performed in a vacuum or an Ar2, N2 gas atmosphere; the pretreatment temperature is 300 DEG C-600 DEG C, and the time is 1 h-12 h; and the pretreatment temperature rising rate is 2 DEG C / min-12 DEG C / min;

[0015] Preferably, the acid pickling pretreatment in S1 includes: after mixing the lignite material and the mixed acid solution, impregnation, filtration, deionized water washing, and drying treatment; the mixed acid solution is: 2-15wt% hydrochloric acid and 5-25wt% hydrofluoric acid, the volume ratio of hydrochloric acid to hydrofluoric acid is 1:1-8, and the volume ratio of mixed acid to lignite powder is 5-30:1; the resistivity of the deionized water is not less than 18MΩcm; the impregnation time of the impregnation operation is 1-10h; the washing times of the deionized water washing are 3-6 times; the drying temperature is 50-180℃, and the drying time is 5-20h;

[0016] Preferably, the ball milling and sieving treatment in S2 is: the mechanical ball milling speed is 100-500rpm, the ball milling time is 5-60min, and the ball-to-powder mass ratio is 1:5-30; the sieving mesh number of the sieving treatment is 50-400;

[0017] Preferably, the mixing ratio of the mixing grinding, the swelling treatment, and the plasma ball milling coating in S3 is 0.5-3; the grinding time is 10-60min; the swelling treatment time is 3-20h; the pretreatment temperature is 25-250℃; the solution required by the swelling treatment is prepared by 0.5-12ml / L of solute and solvent; the solute is one or more of N-methyl morpholine-N-oxide, anhydrous ferric chloride, anhydrous aluminum chloride, methyl formate, trifluoromethanesulfonic acid, NaOH, KOH, LiOH, LiCl, NaCl, [BMIM]CI, HCI, H2SO4; the solvent is one or more of water, DMAc, solution, alcohol solution; the mass ratio of the mixed powder to the solution in the swelling treatment is 1:1-50;

[0018] Preferably, the washing times in S3 are 3-6 times; the drying temperature is 50-180℃, and the drying time is 5-20h;

[0019] Preferably, the plasma ball milling parameters in S3 are: the plasma discharge atmosphere is 5×103-1×105 argon, the dielectric barrier is plastic or ceramic, the dielectric constant of the dielectric barrier is 2-10, the thickness of the dielectric barrier is 3-6mm, the ball-to-powder ratio is 15:1-50:1, the ball milling time is 2h-12h, and the ball mill speed is 960-1400rpm;

[0020] Preferably, the high-temperature carbonization treatment in S4 controls the heating rate to be 2-12℃ / min, the carbonization temperature is 800-2000℃, and the carbonization time is 2-12h; the protective atmosphere is at least one of vacuum atmosphere, nitrogen, argon, or a mixture thereof;

[0021] Another object of the present application is to provide a sodium-ion battery negative electrode material, a preparation method and an application thereof, wherein the sodium-ion battery negative electrode material uses a heterojunction hard carbon material prepared by the above-mentioned preparation method of the heterojunction hard carbon material as a negative electrode active material; the heterojunction hard carbon material is prepared into a hard carbon negative electrode sheet, and is prepared into a sodium-ion battery, and the preparation method comprises the following steps:

[0022] The prepared heterojunction hard carbon material is mixed with conductive carbon black, styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) at a certain mass ratio, and a proper amount of deionized water is added and uniformly mixed, and the mixture is continuously stirred in a high-speed pulper to obtain a slurry; the slurry is uniformly coated on a copper foil and dried in a vacuum drying oven; finally, a hard carbon negative electrode sheet is prepared through rolling and punching; a sodium-ion battery is assembled in a glove box filled with argon and strictly controlled water and oxygen index, with the hard carbon negative electrode sheet as a working electrode, a metal sodium sheet as a counter electrode, a Celgard 2500 polypropylene-based three-layer film as a battery separator, and a 1.0M LiPF6 in EC solution as an electrolyte; and the assembled sodium-ion battery is left to stand for a certain period of time.

[0023] Preferably, the mass ratio of the heterojunction hard carbon material to conductive carbon black, styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) is 90:5:3:2; the temperature in the vacuum drying oven is 80℃, and the drying time is 12 hours; the water and oxygen index is less than 0.01ppm; and the standing time of the standing is 24 hours.

[0024] Preferably, the areal density of the negative electrode sheet prepared according to the above-mentioned preparation method of the heterojunction hard carbon material and the preparation method of the sodium-ion battery negative electrode material is 2mg / cm2~3mg / cm2; the first sodium storage charge specific capacity is 302.44mAhg-1, and the first coulombic efficiency is 89.32%.

[0025] The present application has the following advantages:

[0026] The preparation method of the heterojunction hard carbon material is simple, and uses cheap and readily available reed canary grass and lignite as raw materials; the reed canary grass is treated by low-temperature pre-carbonization, and the lignite is pretreated by acid washing to form a precursor suitable for swelling treatment; then the carbon material is treated by swelling to realize the closed pore structure of the carbon material; then the carbon material is treated by plasma ball milling to enhance the uniformity of the carbon coating; and then the carbon material is treated by high-temperature hard carbonization to realize the rearrangement of the carbon layer and control the pore structure of the hard carbon material, so that a rich closed pore structure is obtained. The heterojunction hard carbon material has a heterojunction hard carbon coating structure inside, and can be applied to a sodium-ion battery.

[0027] The sodium ion battery negative electrode material of the application uses the above-mentioned heterojunction hard carbon material, because the hard carbon material has few surface pores and defects and has rich closed pore structure inside, the first coulomb efficiency and cycle stability are improved, the electrochemical performance of the sodium ion battery is improved, the preparation cost of the hard carbon material is effectively reduced, the cost advantage of the sodium ion battery is increased, and the industrial production is suitable. BRIEF DESCRIPTION OF DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the application, the following will briefly introduce the drawings needed to be used in the description of the embodiments, and obviously, the drawings in the following description are only some embodiments of the application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of these drawings.

[0029] Figure 1 SEM atlas of the hard carbon material prepared for example 5;

[0030] Figure 2 is the first circle charge-discharge curve diagram of the hard carbon negative electrode material provided by example 5 of the application; DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the application will be described clearly and completely in the following with reference to the drawings in the embodiments of the application, and obviously, the described embodiments are only some embodiments of the application, not all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor belong to the protection scope of the application.

[0032] Example 1

[0033] This embodiment provides a heterojunction hard carbon material, and raw materials of the heterojunction hard carbon material include: bamboo, lignite;

[0034] Example 2

[0035] Based on the above-mentioned example 1, in this embodiment, a preparation method of the heterojunction hard carbon material is provided, which includes the following steps:

[0036] S1: the bamboo is washed with deionized water for multiple times, dried by air blowing, and then crushed to obtain a bamboo yellow powder; the bamboo yellow powder is pretreated to obtain a bamboo pre-carbonization powder; the lignite is mechanically ball milled and sieved to obtain a lignite black powder of a certain particle size, and then the lignite black powder is acid-washed and pretreated to obtain a lignite pre-ash removal powder;

[0037] S2: the bamboo pre-carbonization powder and the lignite pre-ash removal powder are mechanically ball milled and sieved in sequence respectively to obtain an intermediate bamboo carbon material and an intermediate lignite material respectively;

[0038] S3: sequentially mixing and grinding the intermediate bamboo charcoal material and the intermediate lignite material, swelling treatment, washing with deionized water and drying treatment to obtain a mixed black powder; adding the mixed black powder into a plasma ball mill, adding anhydrous ethanol for plasma ball milling coating treatment to obtain a carbonized precursor powder;

[0039] S4: high-temperature carbonization treatment of the carbonized precursor powder, then grinding and sieving to obtain the heterojunction hard carbon material.

[0040] Example 3

[0041] Based on the above-mentioned example 2, in this embodiment, preferably, the atmosphere condition of the pre-treatment of the bamboo yellow powder in S1 is carried out in a vacuum or Ar2, N2 gas atmosphere; the pre-treatment temperature is 300-600℃, and the time is 1-12h; the pre-treatment temperature rising rate is 2-12℃ / min;

[0042] In this embodiment, the acid pickling pre-treatment in S1 includes: mixing the lignite material and the mixed acid solution, then dipping, filtering, deionized water washing, and drying treatment;

[0043] In this embodiment, the mixed acid solution is: 2-15wt% hydrochloric acid and 5-25wt% hydrofluoric acid, the volume ratio of hydrochloric acid to hydrofluoric acid is 1:1-8, and the volume ratio of mixed acid to lignite powder is 5-30:1; the resistivity of the deionized water is not less than 18MΩcm; the dipping time of the dipping operation is 1-10h; the washing times of the deionized water washing is 3-6 times; the drying temperature is 50-180℃, and the drying time is 5-20h;

[0044] In this embodiment, the ball milling and sieving treatment in S2 is specifically: the mechanical ball milling speed is 100-500rpm, the ball milling time is 5-60min, the ball-to-material mass ratio is 1:5-30, and the sieving mesh number of the sieving treatment is 50-400;

[0045] In the embodiment, the mixing ratio of the mixing grinding in S3, the swelling treatment, and the plasma ball milling coating is 0.5-3; the grinding time is 10-60 min; the swelling treatment time is 3-20 h; the pretreatment temperature is 25-250℃; the solution required for the swelling treatment is prepared by mixing a solute and a solvent at a ratio of 0.5-12 ml / L; the solute is one or more of N-methylmorpholine-N-oxide, anhydrous ferric chloride, anhydrous aluminum chloride, methylal, triflic acid, NaOH, KOH, LiOH, LiCl, NaCl, [BMIM]CI, HCI, H2SO4; the solvent is one or more of water, DMAc, solution, alcohol solution; the mass ratio of the mixed powder to the solution in the swelling treatment is 1:1-50;

[0046] In the embodiment, the number of washing in S3 is 3-6 times; the drying temperature is 50-180℃, and the drying time is 5-20 h;

[0047] In the embodiment, the plasma ball milling parameters in S3 are as follows: the plasma discharge atmosphere is 5×103-1×105 argon, the dielectric barrier is plastic or ceramic, the dielectric constant of the dielectric barrier is 2-10, the thickness of the dielectric barrier is 3-6 mm, the ball-to-powder ratio is 15:1-50:1, the ball milling time is 2 h-12 h, and the ball milling speed is 960-1400 rpm;

[0048] In the embodiment, the high-temperature carbonization treatment in S4 controls the heating rate to be 2-12℃ / min, the carbonization temperature is 800-2000℃, and the carbonization time is 2-12 h; the protective atmosphere is at least one of vacuum atmosphere, nitrogen, argon, or a mixture thereof;

[0049] Embodiment 4

[0050] Based on the above embodiments 1-3, in the embodiment, a sodium ion battery negative electrode material is provided, which uses the heterojunction hard carbon material prepared in the above embodiments 1-3 as the negative active material of the sodium ion battery; the heterojunction hard carbon material is prepared into a hard carbon negative electrode sheet, and the preparation method comprises the following steps:

[0051] The heterojunction hard carbon material prepared in the above embodiments 1-3 is mixed with conductive carbon black, styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) at a mass ratio of 90:5:3:2, and an appropriate amount of deionized water is added and uniformly mixed, and a slurry is obtained by continuously stirring in a high-speed pulper; the slurry is uniformly coated on a copper foil, and is placed in a vacuum drying oven at 80℃ and dried for 12 hours; finally, a hard carbon negative electrode sheet is prepared through rolling and punching; the areal density of the hard carbon negative electrode sheet is 2-3 mg / cm2;

[0052] Example 5

[0053] Based on the above examples 1-4, in this embodiment, the application of sodium ion battery negative electrode material in sodium ion battery is provided, specifically, the hard carbon negative electrode sheet prepared by the above examples 1-4 is used as the working electrode, the metal sodium sheet is used as the counter electrode, the Celgard2500 polypropylene-based three-layer film is used as the battery separator, and the 1.0M LiPF6 in EC solution is used as the electrolyte. The sodium ion battery is assembled in the glove box filled with argon and strictly controlled to less than 0.01 ppm of water and oxygen index;

[0054] After the assembled lithium ion battery is placed for 24 hours, the performance test is carried out by using the LAND battery tester, the charge and discharge test voltage is 0-1.5V, and the current density is 0.1C (1C is 280mAhg -1 ). The charge and discharge curve of the hard carbon negative electrode is shown in Figure 2 , the first sodium storage specific capacity is 302.44mAhg -1 , and the first coulombic efficiency is 89.32%.

[0055] Example 6

[0056] Based on the above examples 1-5, in this embodiment, three kinds of hard carbon materials are provided, and the preparation method is the same as examples 1-5, the difference is that: the pretreatment temperature in S1 of the first kind is 300℃, the pre-carbonization time is 10 hours, and the heating rate is 12℃ / min;

[0057] The pretreatment temperature in S1 of the second kind is 400℃, the pre-carbonization time is 6 hours, and the heating rate is 8℃ / min; the pretreatment temperature in S1 of the third kind is 600℃, the pre-carbonization time is 1 hour, and the heating rate is 2℃ / min; the three kinds of hard carbon materials prepared are respectively prepared into hard carbon negative electrode sheets, and assembled into sodium ion batteries, and the specific preparation process remains the same as example 4.

[0058] The sodium storage specific capacity of the hard carbon negative electrode prepared by the first kind is 289.21mAhg-1, and the coulombic efficiency is 87.63%; the sodium storage specific capacity of the hard carbon negative electrode prepared by the second kind is 288.34mAhg-1, and the coulombic efficiency is 88.72%; the sodium storage specific capacity of the hard carbon negative electrode prepared by the third kind is 286.45mAhg-1, and the coulombic efficiency is 87.23%.

[0059] Example 7

[0060] Based on the above embodiment 1-embodiment 5, this embodiment provides three kinds of hard carbon materials, the preparation method is same as embodiment 1-embodiment 5, the difference is that: the first kind of mixed acid of acid mixed pretreatment in S1 is 10wt% hydrochloric acid and 10wt% hydrofluoric acid, the immersion time is 4h; the second kind of mixed acid of acid mixed pretreatment in S1 is 15wt% hydrochloric acid and 15wt% hydrofluoric acid, the immersion time is 2h; the third kind of mixed acid in step (5) is 15wt% hydrochloric acid and 25wt% hydrofluoric acid, the immersion time is 1h;

[0061] The three kinds of hard carbon materials prepared are respectively prepared into hard carbon negative electrode sheets, and are respectively assembled into sodium ion batteries, and the specific preparation process remains the same as that of embodiment 1-embodiment 5.

[0062] The sodium storage specific capacity of the first kind of prepared hard carbon negative electrode is 249.9mAhg-1, and the coulombic efficiency is 87.6%; the sodium storage specific capacity of the second kind of prepared hard carbon negative electrode is 242.6mAhg-1, and the coulombic efficiency is 88.2%, and the sodium storage specific capacity of the third kind of prepared hard carbon negative electrode is 249.5mAhg-1, and the coulombic efficiency is 87.3%.

[0063] Embodiment 8

[0064] Based on the above embodiment 1-embodiment 5, in this embodiment, three kinds of hard carbon materials are provided, and the preparation method is same as embodiment 1-embodiment 5, the difference is that: the mechanical ball milling time in S2 of the first kind is 40min, and the ball milling speed is 200rpm; the mechanical ball milling time in S2 of the second kind is 25min, and the ball milling speed is 400rpm; the mechanical ball milling time in S2 of the third kind is 10min, and the ball milling speed is 500rpm;

[0065] The three kinds of hard carbon materials are used as raw materials to prepare hard carbon negative electrode sheets, and are respectively assembled into sodium ion batteries, and the specific preparation process remains the same as that of embodiment 1-embodiment 5.

[0066] The sodium storage specific capacity of the first kind of prepared hard carbon negative electrode is 292.66mAhg-1, and the coulombic efficiency is 87.36%; the sodium storage specific capacity of the second kind of prepared hard carbon negative electrode is 293.53mAhg-1, and the coulombic efficiency is 87.13%, and the sodium storage specific capacity of the third kind of prepared hard carbon negative electrode is 292.24mAhg-1, and the coulombic efficiency is 86.87%.

[0067] Embodiment 9

[0068] Based on the above examples 1-5, in this embodiment, ten kinds of hard carbon materials are provided, the preparation method is consistent with examples 1-5, the difference is that: the mixing mass ratio of S3 in the first kind is 2:1; the mixing mass ratio of S3 in the second kind is 1:2; the swelling treatment of S3 in the third kind uses solute of methylal and N-methylmorpholine-N-oxide; the swelling treatment of S3 in the fourth kind uses solute of methylal and anhydrous ferric chloride; the swelling treatment of S3 in the fifth kind uses solute of methylal and triflic acid; the swelling treatment of S3 in the sixth kind uses solute of methylal and NaOH; the swelling treatment of S3 in the seventh kind uses solute of methylal and KOH; the ball milling speed of S3 in the eighth kind is 1100 rpm, and the ball milling time is 8h; the ball milling speed of S3 in the ninth kind is 1300 rpm, and the ball milling time is 4h; the ball milling speed of S3 in the tenth kind is 1400 rpm, and the ball milling time is 2h;

[0069] The preparation of hard carbon negative electrode sheets is carried out respectively with the ten kinds of hard carbon materials as raw materials, and sodium ion batteries are assembled respectively, and the specific preparation process remains consistent with examples 1-5.

[0070] The sodium storage specific capacity of the hard carbon negative electrode prepared in the first kind is 290.11 mAhg-1, and the coulombic efficiency is 87.73%; the sodium storage specific capacity of the hard carbon negative electrode prepared in the second kind is 287.63 mAhg-1, and the coulombic efficiency is 86.46%; the sodium storage specific capacity of the hard carbon negative electrode prepared in the third kind is 279.73 mAhg-1, and the coulombic efficiency is 85.36%; the sodium storage specific capacity of the hard carbon negative electrode prepared in the fourth kind is 275.44 mAhg-1, and the coulombic efficiency is 84.27%; the sodium storage specific capacity of the hard carbon negative electrode prepared in the fifth kind is 278.96 mAhg-1, and the coulombic efficiency is 85.27%; the sodium storage specific capacity of the hard carbon negative electrode prepared in the sixth kind is 269.54 mAhg-1, and the coulombic efficiency is 83.33%; the sodium storage specific capacity of the hard carbon negative electrode prepared in the seventh kind is 271.38 mAhg-1, and the coulombic efficiency is 84.73%; the sodium storage specific capacity of the hard carbon negative electrode prepared in the eighth kind is 282.45 mAhg-1, and the coulombic efficiency is 86.25%; the sodium storage specific capacity of the hard carbon negative electrode prepared in the ninth kind is 289.15 mAhg-1, and the coulombic efficiency is 84.16%; the sodium storage specific capacity of the hard carbon negative electrode prepared in the tenth kind is 278.16 mAhg-1, and the coulombic efficiency is 86.55%.

[0071] Example 10

[0072] Based on the above examples 1-5, in this embodiment, three kinds of hard carbon materials are provided, and the preparation method is the same as that of examples 1-5, the difference is that: the high temperature carbonization temperature of S4 in the first kind is 1000℃, the pre-carbonization time is 8 hours, and the heating rate is 12℃ / min; the pre-carbonization temperature of S1 in the second kind is 1600℃, the pre-carbonization time is 4 hours, and the heating rate is 8℃ / min; the pre-carbonization temperature of S1 in the third kind is 1800℃, the pre-carbonization time is 2 hours, and the heating rate is 5℃ / min; the three kinds of hard carbon materials are used as raw materials to prepare hard carbon negative electrode sheets, and are assembled into sodium ion batteries, and the specific preparation process is the same as that of examples 1-5

[0073] The specific capacity of the prepared hard carbon negative electrode of the first kind is 270.54 mAhg-1, and the coulombic efficiency is 84.45%; the specific capacity of the prepared hard carbon negative electrode of the second kind is 268.46 mAhg-1, and the coulombic efficiency is 82.11%; the specific capacity of the prepared hard carbon negative electrode of the third kind is 261.37 mAhg-1, and the coulombic efficiency is 81.56%;

[0074] Comparative example 1

[0075] This embodiment provides a kind of hard carbon material, and the preparation method is the same as that of examples 1-5, the difference is that: the low-temperature pre-carbonization step of reed bamboo is less, and the hard carbon material is used as raw material to prepare hard carbon negative electrode sheet, and is assembled into sodium ion battery, and the specific preparation process is the same as that of examples 1-5.

[0076] The hard carbon material is used as raw material to prepare hard carbon negative electrode sheet, and is assembled into sodium ion battery, and the specific preparation process is the same as that of examples 1-5.

[0077] The specific capacity of the prepared hard carbon negative electrode of the first kind is 270.54 mAhg-1, and the coulombic efficiency is 84.45%; the specific capacity of the prepared hard carbon negative electrode of the second kind is 268.46 mAhg-1, and the coulombic efficiency is 82.11%; the specific capacity of the prepared hard carbon negative electrode of the third kind is 261.37 mAhg-1, and the coulombic efficiency is 81.56%;

[0078] Comparative example 2

[0079] This embodiment provides a kind of hard carbon material, and the preparation method is the same as that of examples 1-5, the difference is that: the swelling treatment step is less, and the hard carbon material is used as raw material to prepare hard carbon negative electrode sheet, and is assembled into sodium ion battery, and the specific preparation process is the same as that of examples 1-5.

[0080] The specific capacity of the prepared hard carbon negative electrode of the first kind is 270.54 mAhg-1, and the coulombic efficiency is 84.45%; the specific capacity of the prepared hard carbon negative electrode of the second kind is 268.46 mAhg-1, and the coulombic efficiency is 82.11%; the specific capacity of the prepared hard carbon negative electrode of the third kind is 261.37 mAhg-1, and the coulombic efficiency is 81.56%;

[0081] Comparative example 3

[0082] The embodiment provides a hard carbon material, a preparation method of which is same with that in Embodiment 1-Embodiment 5, except that: the plasma ball milling is changed into ordinary mechanical ball milling, the mechanical ball milling time is 30 min, the ball milling rotating speed is 300 rpm, and the ball-to-material mass ratio is 10:1; the hard carbon material is used as raw material to prepare a hard carbon negative plate, and is assembled into a sodium ion battery, and the specific preparation process is same with that in Embodiment 1-Embodiment 5.

[0083] The specific surface area of the hard carbon material is 1 100 m2g-1, the sodium storage specific capacity of the hard carbon negative electrode prepared from the material is 260.15 mAhg-1, and the coulombic efficiency is 75.26%;

[0084] The hard carbon negative electrode materials prepared in Embodiment 6-Embodiment 10 and Comparative Examples 1-3 are assembled into sodium ion batteries, and the first charge specific capacity and the first cycle coulombic efficiency are tested, and the test results are shown in Table 1 and Table 2. Figure 2 and Table 1.

[0085] Table 1

[0086]

[0087]

[0088] In summary, from Table 1, it can be seen that in the embodiments, only the parameters of the steps are adjusted, and the first cycle charge specific capacity and the coulombic efficiency are not greatly affected, and the overall first cycle coulombic efficiency is more than 80%. From Embodiment 5 and Comparative Example 1, it can be seen that, without the low-temperature pre-carbonization step of the reed canary grass, the subsequent swelling is not complete, which leads to the fact that the carbon cannot be coated by plasma ball milling, and finally the coulombic efficiency is relatively low; based on Embodiment 5 and Comparative Example 2, it can be seen that, without the swelling treatment, the final carbon structure will be affected, and the sodium embedding and extraction will be affected; based on Embodiment 5 and Comparative Example 3, it can be seen that, without the plasma ball milling, the uniformity of the carbon coating will be finally affected, and the first cycle coulombic efficiency is low.

[0089] The preferred embodiments disclosed above are only used to help explain the present application. The preferred embodiments do not describe all the details, and the application is not limited to the specific embodiments described. Obviously, many modifications and changes can be made according to the content of the present application. The embodiments are selected and described in the present application in order to better explain the principles and practical applications of the present application, so that those skilled in the art can well understand and use the present application. The present application is limited by the claims and the entire scope and equivalents thereof.

Claims

1. A method for producing a hetero-junction hard carbon material, characterized by, The method comprises the following steps: S1: washing the bamboo reed with deionized water multiple times, drying by air blowing, and then crushing to obtain a yellow bamboo reed powder; pretreating the yellow bamboo reed powder to obtain a bamboo reed pre-carbonization powder; mechanically ball-milling and sieving lignite to obtain a black lignite powder of a certain particle size, and then acid-washing and pretreating the black lignite powder to obtain a lignite pre-ash removal powder; S2: sequentially performing mechanical ball-milling and sieving treatment on the bamboo reed pre-carbonization powder and the lignite pre-ash removal powder to obtain an intermediate bamboo reed carbon material and an intermediate lignite material, respectively; S3: sequentially performing mixing and grinding, swelling treatment, washing with deionized water, and drying treatment on the intermediate bamboo reed carbon material and the intermediate lignite material to obtain a mixed black powder; adding the mixed black powder into a plasma ball mill, and adding anhydrous ethanol to perform plasma ball-milling coating treatment to obtain a carbonization precursor powder; S4: performing high-temperature carbonization treatment on the carbonization precursor powder, and then performing grinding and sieving to obtain the heterojunction hard carbon material.

2. The method for preparing heterojunction hard carbon material according to claim 1, characterized in that, In the S1, the number of deionized water washing is 3-6 times; the drying temperature is 50-180 DEG C; the drying time is 5-20 h; the crushing time is 20 min-50 min; in the S1, the pretreatment of the yellow bamboo reed powder is performed in a vacuum, Ar or N2 atmosphere; the pretreatment temperature is 300 DEG C-600 DEG C, and the time is 1 h-12 h; the heating rate of the pretreatment is 2 DEG C / min-12 DEG C / min; the acid-washing pretreatment in the S1 comprises the following steps: mixing the lignite material and a mixed acid solution, impregnating, filtering, washing with deionized water, and drying treatment; the mixed acid solution is a mixed acid solution with a concentration of 2-15 wt% hydrochloric acid and 5-25 wt% hydrofluoric acid, and the volume ratio of hydrochloric acid to hydrofluoric acid is 1:1-8; the resistivity of the deionized water in the acid-washing pretreatment is not less than 18 MΩ·cm; the impregnation time of the impregnation operation is 1-10 h; the number of washing with deionized water in the acid-washing pretreatment is 3-6 times; and the drying temperature is 50-180 DEG C, and the drying time is 5-20 h.

3. The method of claim 1, wherein the hetero-junction hard carbon material is prepared by the steps of: preparing a mixture of a carbon source and a metal source; and annealing the mixture at a temperature of 800-1,200°C in an inert gas atmosphere. In the S2, the mechanical ball-milling and sieving treatment is as follows: the mechanical ball-milling speed is 100-500 rpm, the ball-milling time is 5-60 min, the ball-to-material mass ratio is 1:5-30, and the sieving mesh number of the sieving treatment is 50-400.

4. The method of claim 1, wherein the hetero-junction hard carbon material is prepared by the steps of: preparing a mixture of a carbon source and a metal source; and annealing the mixture at a temperature of 800-1,200°C in an inert gas atmosphere. The S3 grinding time is 10-60 min; the swelling treatment time is 3-20 h; the solution required for the swelling treatment is prepared by dissolving a solute in a solvent at a ratio of 0.5-12 ml / L; the solute is one or more of N-methylmorpholine-N-oxide, anhydrous ferric chloride, anhydrous aluminum chloride, methylal, triflic acid, NaOH, KOH, LiOH, LiCl, NaCl, [BMIM]Cl, HCl, H2SO4; the solvent is one or more of water, DMAc solution, alcohol solution; the mass ratio of the mixed powder to the solution in the swelling treatment is 1:1-50; the number of washing in S3 is 3-6 times; the drying temperature is 50-180℃, and the drying time is 5-20 h; the plasma ball milling parameters in S3 are: the dielectric barrier is polytetrafluoroethylene or ceramic, the dielectric constant of the dielectric barrier is 2-10, the thickness of the dielectric barrier is 3-6 mm, the ball-to-material ratio is 15:1-50:1, the ball milling time is 2 h-12 h, and the ball mill rotation speed is 960-1400 rpm.

5. The method of claim 1, wherein the hetero-junction hard carbon material is prepared by a process comprising: The high-temperature carbonization treatment in S4 controls the heating rate to be 2-12℃ / min, the carbonization temperature to be 800-2000℃, and the carbonization time to be 2-12 h; the protective atmosphere is vacuum atmosphere, nitrogen, argon or a mixture of nitrogen and argon.

6. A hetero-junction hard carbon material, characterized by: The heterojunction hard carbon material is prepared by the method in any one of claims 1-5.

7. A sodium-ion battery anode material, characterized in that, The heterojunction hard carbon material in claim 6 is used as a negative active material; the heterojunction hard carbon material is prepared into a hard carbon negative electrode sheet, and a sodium ion battery is prepared, the preparation method comprising the following steps: The prepared heterojunction hard carbon material is mixed with conductive carbon black, butadiene styrene rubber and carboxymethyl cellulose at a certain mass ratio, and an appropriate amount of deionized water is added and uniformly mixed, and a slurry is obtained by continuously stirring in a high-speed pulper; the slurry is uniformly coated on a copper foil and dried in a vacuum drying oven; finally, a hard carbon negative electrode sheet is prepared through rolling and punching; a sodium ion battery is assembled in an argon-filled glove box with strictly controlled water and oxygen index, using the obtained hard carbon negative electrode sheet as a working electrode, a metal sodium sheet as a counter electrode, a Celgard 2500 polypropylene-based three-layer film as a battery separator, and 1.0 M LiPF6 in EC solution as an electrolyte; the assembled sodium ion battery is left to stand for several hours.

8. The sodium-ion battery anode material of claim 7, wherein, The mass ratio of the heterojunction hard carbon material to conductive carbon black, butadiene styrene rubber and carboxymethyl cellulose is 90:5:3:2; the temperature in the vacuum drying oven is 80℃, and the drying time is 12 hours; the water and oxygen index is less than 0.01 ppm; the standing time is 24 hours. The mass ratio of the heterojunction hard carbon material to conductive carbon black, butadiene styrene rubber and carboxymethyl cellulose is 90:5:3:2; the temperature in the vacuum drying oven is 80℃, and the drying time is 12 hours; the water and oxygen index is less than 0.01 ppm; the standing time is 24 hours.

9. A sodium-ion battery, characterized in that, The negative electrode material of the battery is the sodium ion battery negative electrode material of claim 7 or 8, and the area density of the negative electrode sheet is 2 mg / cm 2 ~ 3 mg / cm 2 ; the specific capacity of the first sodium storage charge is 302.44 mAh g -1 , and the first coulombic efficiency is 89.32%.

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