A method for preparing hard carbon negative electrode material based on double cross-linking reaction of organophosphoric acid and Schiff base and its application in sodium battery

Abstract

A method for preparing a hard carbon negative electrode material based on a double cross-linking reaction of organophosphoric acid and Schiff base and its application in sodium batteries, the method comprising the following steps: step 1, cross-linking biomass and organophosphoric acid with C-O-P bonds; step 2, converting the material obtained in the first step into aldehyde groups (-CHO) by oxidation with an oxidizing acid; step 3, secondary cross-linking the -CHO of the material obtained in the second step with the -NH2 in the diamine compound by Schiff base reaction; step 4, carbonizing the material obtained in the third step at high temperature in an inert atmosphere, and assembling it into a sodium ion battery after cooling. Compared with the prior art, the present invention has the following advantages: (1) the operation method is simple and reliable, takes less time, and does not require the use of high-end instruments. (2) the improvement efficiency is excellent and can be mass-produced.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium ion batteries, and specifically relates to a method for preparing a hard carbon negative electrode material based on a double cross-linking reaction of organic phosphoric acid and Schiff base, and an application thereof in sodium batteries. Background Art

[0002] In recent years, there has been a worldwide consensus on reconstructing the energy system and pursuing sustainable development. Replacing traditional fossil fuels with renewable energy is considered an effective strategy to achieve this goal. However, due to the intermittent nature of renewable energy (such as wind and solar energy), energy storage systems are required in practical applications to alleviate time domain limitations and relieve grid pressure. Batteries, as a portable chemical energy storage device with high conversion efficiency, have played a key role in many fields in recent years. In large-scale energy storage solutions, sodium-ion batteries have attracted much attention due to their abundant sodium resources, good low-temperature performance, and high cost-effectiveness potential.

[0003] The development of high-performance sodium-ion batteries depends largely on the progress of electrode materials, especially the limited selection of negative electrode materials. Therefore, the development of new negative electrode materials that meet the special needs of sodium-ion batteries is crucial for their practical application. Among many carbon-based materials, hard carbon stands out as a candidate material for large-scale electrochemical energy storage. Hard carbon has a low operating voltage (<0.3V vs. Na + / Na), an appropriate interlayer spacing (>0.34nm), and numerous sodium adsorption sites demonstrate a high theoretical sodium storage capacity, which is expected to significantly improve the energy density of sodium-ion batteries. However, hard carbon anodes still face several key challenges, such as low reversible capacity, low initial Coulombic efficiency, poor rate performance, and limited long-term cycling stability. Therefore, developing a simple and effective hard carbon preparation strategy is of great significance for promoting the practical application of sodium-ion batteries. Summary of the Invention

[0004] The purpose of the present invention is to solve the problems of low reversible capacity, low first-cycle coulombic efficiency, and poor rate performance of hard carbon negative electrodes, and to provide a method for preparing hard carbon negative electrode materials based on a double cross-linking reaction of organic phosphoric acid and Schiff base and its application in sodium batteries, wherein organic phosphonic acid and organic amine are used as cross-linking agents in sequence to improve the micromorphology and electrochemical properties of biomass-derived hard carbon negative electrodes.

[0005] The purpose of the present invention is achieved through the following technical solutions:

[0006] A method for preparing a hard carbon negative electrode material based on a double cross-linking reaction of an organic phosphoric acid and a Schiff base, the method comprising:

[0007] Step 1: Biomass, organic phosphonic acid, and water are mixed in a mass ratio of 1:1 to 2:8, stirred at room temperature for 10 hours, filtered, and dried in an oven for 12 hours to obtain a first precursor. This step causes the first cross-linking reaction to occur within the biomass, generating a large number of COP groups.

[0008] Step 2: Precursor No. 1, an oxidizing acid, and water are mixed in a mass ratio of 1:1 to 2:8, stirred at room temperature for 10 hours, filtered, and dried in an oven for 12 hours to obtain precursor No. 2; in this step, precursor No. 1 is oxidized with an oxidizing acid to convert -OH to -CHO for the subsequent Schiff base reaction;

[0009] Step 3: The second precursor and the diamine compound undergo a Schiff base reaction to perform a second crosslinking. The second precursor, the diamine compound, and water are mixed in a mass ratio of 1:1 to 2:8, and a Schiff base reaction is performed at 80°C. After stirring for 10 hours, a large amount of -RC=N- groups are generated. The mixture is filtered and placed in an oven to dry for 12 hours to obtain the third precursor.

[0010] Step 4: Add the No. 3 precursor into an alumina crucible, place it in a tube furnace, introduce inert gas as a protective gas, carbonize at high temperature, and cool naturally to obtain an N / P co-doped hard carbon negative electrode material.

[0011] Furthermore, in step one, the biomass includes at least one of agricultural by-products such as sesame shells, almond shells, corn cobs, and corn stalks.

[0012] Furthermore, in step 1, the organic phosphonic acid includes at least one of aminotris(methylenephosphonic acid), ethylenediaminetetra(methylenephosphonic acid), phytic acid, and phosphonoacetic acid.

[0013] Furthermore, in step 2, the oxidizing acid includes at least one of nitric acid, perchloric acid, and periodic acid.

[0014] Furthermore, in step three, the diamine compound includes at least one of ethylenediamine, 1,2-diaminobenzene, diethylenetriamine, and triethylenetetramine.

[0015] Furthermore, in step 4, the high-temperature carbonization is specifically performed by heating from room temperature to 1200-1400° C. at a rate of 5° C. / min, and keeping the temperature for 2-3 hours.

[0016] An application of the hard carbon negative electrode material prepared by the above preparation method through a double cross-linking reaction in a sodium ion battery.

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] (1) Based on this double cross-linking effect, the cellulose chains widely present in biomass can be tightly arranged, and rich N / P elements can be in situ doped in the biomass, so that N / P co-doped hard carbon materials with lower specific surface area can be prepared in the subsequent high-temperature carbonization. Based on the synergistic effect of the above two points, the prepared hard carbon materials can have higher reversible capacity, initial coulombic efficiency, cycle stability and excellent rate performance.

[0019] (2) The operation is simple and effective, takes little time and requires few instruments.

[0020] (3) The improvement effect is excellent and can be achieved in large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The constant current charge and discharge diagram of the half-cell before and after double cross-linking in Example 1 is compared.

[0022] Figure 2 This is a comparison of the half-cell constant current charge and discharge diagram before and after double cross-linking in Example 2.

[0023] Figure 3 This is a comparison of the constant current charge and discharge diagram of the half-cell before and after double cross-linking in Example 3.

[0024] Figure 4 This is a half-cell rate performance diagram comparing before and after double cross-linking.

[0025] Figure 5 This is a comparison of the long cycle performance of the half-cell before and after double cross-linking.

[0026] The control group was a hard carbon negative electrode prepared without double cross-linking reaction. DETAILED DESCRIPTION

[0027] The technical solution of the present invention is further described below with reference to the accompanying drawings, but is not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention that does not depart from the spirit and scope of the technical solution of the present invention should be included in the scope of protection of the present invention.

[0028] In the present invention, biomass contains a large number of long cellulose chains, which can form POC bonds with the PO in the organic phosphonic acid, thereby achieving crosslinking through the organic phosphonic acid, and assembling the parallel cellulose long chains into a cellulose network. Subsequently, an oxidizing acid is used to oxidize the large number of -OH functional groups in the cellulose network into -CHO functional groups. The cellulose network is then placed in an aqueous solution of a diamine compound to undergo a Schiff base reaction, further achieving crosslinking between the chains.

[0029] Example 1:

[0030] Step 1: Mix aminotri(methylenephosphonic acid), almond shells, and water in a mass ratio of 1:1:8 in a beaker equipped with a magnetic stirrer. Stir at room temperature for 10 hours, filter, rinse with deionized water until neutral, and dry in an oven for 12 hours to obtain precursor No. 1.

[0031] Step 2: Mix precursor No. 1, nitric acid, and water in a beaker equipped with a magnetic stirrer in a mass ratio of 1:2:8. Stir at room temperature for 10 hours, filter, rinse with deionized water until neutral, and dry in an oven for 12 hours to obtain precursor No. 2.

[0032] Step 3: Mix precursor No. 2, ethylenediamine, and water in a mass ratio of 1:2:8 in a beaker equipped with a magnetic stirrer. Stir at 80°C for 10 hours, filter, rinse with deionized water several times, and dry in an oven for 12 hours to obtain precursor No. 3.

[0033] Step 4: Add 10g of precursor No. 3 into an alumina crucible, place it in a tube furnace, introduce argon as a protective gas, heat to 1200℃ at a rate of 5℃ / min, keep warm for 3h, and cool naturally to obtain N / P co-doped hard carbon material.

[0034] Example 2:

[0035] Step 1: Mix phytic acid, corn cobs, and water in a beaker equipped with a magnetic stirrer in a mass ratio of 1:1:8. Stir at room temperature for 10 hours, filter, rinse with deionized water until neutral, and dry in an oven for 12 hours to obtain precursor No. 1.

[0036] Step 2: Mix precursor No. 1, perchloric acid, and water in a beaker equipped with a magnetic stirrer in a mass ratio of 1:1:8. Stir at room temperature for 10 hours, filter, rinse with deionized water until neutral, and dry in an oven for 12 hours to obtain precursor No. 2.

[0037] Step 3: Mix precursor No. 2, 1,2-diaminobenzene, and water in a mass ratio of 1:1:8 in a beaker equipped with a magnetic stirrer. Stir at 80°C for 10 hours, filter, rinse with deionized water several times, and dry in an oven for 12 hours to obtain precursor No. 3.

[0038] Step 4: Add 10g of precursor No. 3 into an alumina crucible, place it in a tubular furnace, introduce argon as a protective gas, heat to 1300℃ at a rate of 5℃ / min, keep warm for 2h, and then cool naturally to obtain N / P co-doped hard carbon material.

[0039] Example 3:

[0040] Step 1: Mix ethylenediaminetetramethylenephosphonic acid, sesame shells and water in a mass ratio of 1:2:8 in a beaker equipped with a magnetic stirrer. Stir at room temperature for 10 hours, filter, rinse with deionized water until neutral, and dry in an oven for 12 hours to obtain precursor No. 1.

[0041] Step 2: Mix precursor No. 1, periodic acid, and water in a beaker equipped with a magnetic stirrer in a mass ratio of 1:2:8. Stir at room temperature for 10 hours, filter, rinse with deionized water until neutral, and dry in an oven for 12 hours to obtain precursor No. 2.

[0042] Step 3: Mix precursor No. 2, 1,2-diaminobenzene, and water in a mass ratio of 1:1:8 in a beaker equipped with a magnetic stirrer. Stir at 80°C for 10 hours, filter, rinse with deionized water several times, and dry in an oven for 12 hours to obtain precursor No. 3.

[0043] Step 4: Add 10g of precursor No. 3 into an alumina crucible, place it in a tubular furnace, introduce argon as a protective gas, heat to 1400℃ at a rate of 5℃ / min, keep warm for 2h, and then cool naturally to obtain N / P co-doped hard carbon material.

[0044] Comparative Example

[0045] The untreated biomass was washed with water to remove dust and ground into powder, and then directly placed in a tube furnace for high-temperature carbonization using the same process parameters as step 4 of Example 1.

[0046] The hard carbon materials prepared in the comparative example and the example were respectively used as negative electrode materials of sodium ion batteries and assembled into button batteries. The preparation method was as follows:

[0047] In 1000mg of water, add 180mg of sample, 10mg of Super P (conductive agent), and 10mg of carboxymethyl cellulose (binder), stir thoroughly for 30 minutes, evenly apply the mixed slurry on a flat copper foil, dry and slice to obtain the electrode; use 1mol / L NaPF6 diethylene glycol dimethyl ether solution as the electrolyte; use metallic sodium as the counter electrode.

[0048] Depend on Figures 1 to 3 It can be seen that the hard carbon negative electrodes prepared by the double cross-linking reaction in each embodiment have a larger reversible capacity and a higher first cycle coulombic efficiency (ICE) than those in the comparative example. Figure 4 This shows that Example 1 prepared by double cross-linking has significantly improved rate performance. Figure 5 This shows that the double cross-linking reaction also plays a significant role in improving the long-cycle performance of sodium-ion batteries.

Claims

1. A method for preparing a hard carbon negative electrode material based on a double cross-linking reaction of an organophosphoric acid and a Schiff base, characterized in that: The method is: Step 1: Mix organic phosphonic acid or phytic acid with biomass and water in a mass ratio of 1-2:1:8, stir at room temperature for 10 hours, filter, and dry in an oven for 12 hours to obtain precursor No. 1; Step 2: Precursor No. 1, oxidizing acid, and water are mixed in a mass ratio of 1:1 to 2:8, stirred at room temperature for 10 h, filtered, and dried in an oven for 12 h to obtain precursor No. 2; Step 3: Precursor No. 2, diamine compound, and water are mixed in a mass ratio of 1:1 to 2:8, and a Schiff base reaction is carried out at 80°C. After stirring for 10 hours, the mixture is filtered and dried in an oven for 12 hours to obtain precursor No.

3. Step 4: Add the No. 3 precursor into an alumina crucible, place it in a tube furnace, introduce inert gas as a protective gas, carbonize at high temperature, and cool naturally to obtain an N / P co-doped hard carbon negative electrode material.

2. The method for preparing a hard carbon negative electrode material based on a double cross-linking reaction of an organophosphoric acid and a Schiff base according to claim 1, characterized in that: In step 1, the biomass includes at least one of sesame shells, almond shells, corn cobs, and corn stalks.

3. The method for preparing a hard carbon negative electrode material based on a double cross-linking reaction of an organophosphoric acid and a Schiff base according to claim 1, characterized in that: In step 1, the organic phosphonic acid includes at least one of aminotris(methylenephosphonic acid), ethylenediaminetetra(methylenephosphonic acid), and phosphonoacetic acid.

4. The method for preparing a hard carbon negative electrode material based on a double cross-linking reaction of an organophosphoric acid and a Schiff base according to claim 1, characterized in that: In step 2, the oxidizing acid includes at least one of nitric acid, perchloric acid, and periodic acid.

5. The method for preparing a hard carbon negative electrode material based on a double cross-linking reaction of an organophosphoric acid and a Schiff base according to claim 1, characterized in that: In step 3, the diamine compound includes at least one of ethylenediamine and 1,2-diaminobenzene.

6. The method for preparing a hard carbon negative electrode material based on a double cross-linking reaction of an organophosphoric acid and a Schiff base according to claim 1, characterized in that: In step 4, the high-temperature carbonization is specifically carried out as follows: heating from room temperature to 1200-1400°C at a rate of 5°C / min, and keeping the temperature for 2-3 hours.

7. Use of a hard carbon negative electrode material prepared by the preparation method according to any one of claims 1 to 6 in a sodium ion battery.

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