Preparation method and application of hard carbon negative electrode material for sodium ion battery

Abstract

The application relates to the technical field of battery electrode materials, in particular to a preparation method and application of a hard carbon negative electrode material for a sodium ion battery. The preparation method comprises the following steps: uniformly mixing resorcinol, a template agent and an ethanol aqueous solution, then adding a formaldehyde solution, and reacting to obtain a resin gel; in an inert atmosphere, the resin gel is heated at a specific heating rate, then is baked, and after acid washing and drying, a resin powder is obtained; the resin powder is mixed with g-C3N4 and is ground to obtain a mixed powder; in the inert atmosphere, the mixed powder is heated at a specific heating rate, is baked, and after cooling, a hard carbon negative electrode material is obtained. The hard carbon negative electrode material preparation method provided by the application has the advantages of simple process, and the hard carbon negative electrode material obtained by the method has the advantages of rich micropore structure, high reversible capacity and good cycle stability.

Description

TECHNICAL FIELD

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

[0002] The shortage of lithium resources and high cost are great difficulties that currently restrict the development of lithium ion batteries. Under this background, sodium ion batteries, which are similar in chemical properties to lithium batteries, have a significant cost advantage and are the most promising energy storage technology. Ordinary commercial graphite is difficult to match sodium ion batteries, while hard carbon has more sodium storage sites and can provide more capacity. Therefore, hard carbon is considered to be the most promising electrode material for sodium ion batteries.

[0003] The method for preparing a hard carbon negative electrode material in the prior art has the disadvantages of complex process flow, low reversible capacity and poor cycle stability of the prepared hard carbon negative electrode material. SUMMARY

[0004] In view of the above technical problems, the present application provides a preparation method and application of a hard carbon negative electrode material for a sodium ion battery. The method has a simple process flow, solves the problem of complex process flow in the prior art, and the hard carbon negative electrode material obtained by the method has a rich microporous structure, high reversible capacity and good cycle stability.

[0005] To solve the above technical problems, the present application adopts the following technical solutions:

[0006] In a first aspect, the present application provides a preparation method of a hard carbon negative electrode material for a sodium ion battery, comprising the following operations: S1, uniformly mixing resorcinol, a template agent and an ethanol aqueous solution, then adding a formaldehyde solution, and obtaining a resin gel by reaction, wherein the template agent is a carbonate of an alkali metal and / or a carbonate of an alkaline earth metal;

[0007] S2, in an inert atmosphere, heating the resin gel to 600-800 DEG C at a heating rate of 5-10 DEG C / min, taking out after heat preservation and calcination for 1-2h, acid washing and drying to obtain a resin powder;

[0008] S3, mixing and grinding the resin powder with g-C3N4 to obtain a mixed powder;

[0009] S4, in an inert atmosphere, heating the mixed powder to 1200-1500 DEG C at a heating rate of 5-10 DEG C / min, heat preservation for 2-3h, and cooling to obtain the hard carbon negative electrode material.

[0010] The hard carbon negative electrode material preparation method has the advantages of simple process and easy operation. The hard carbon negative electrode material obtained by the method has a large amount of pseudo-graphite structure and rich microporous structure. The structures promote the storage of sodium in the hard carbon negative electrode material, and give the hard carbon negative electrode material a high reversible capacity and excellent cycle stability.

[0011] In the hard carbon negative electrode material preparation method, the added alkali metal carbonate template agent or alkaline earth metal carbonate template agent can provide a matrix for the generation of phenolic resin, accelerate the formation of resin gel, and significantly improve the synthesis efficiency. The condition parameters of the first step of sintering can decompose the alkali metal carbonate template agent or alkaline earth metal carbonate template agent in the resin gel into a large amount of metal oxide and carbon dioxide, and release gas by sintering the resin gel. The escape of the gas promotes the preliminary formation of the microporous structure inside the resin powder. After a large amount of metal oxide and the remaining un-sintered template agent are removed by acid washing, the resin powder with rich microporous structure is obtained by drying. The rich microporous structure provides more sites for sodium filling, improves the storage capacity of sodium in the hard carbon negative electrode material, and further improves the reversible capacity of the sodium ion battery hard carbon negative electrode material. After the resin powder with rich microporous structure is mixed and ground with g-C3N4, the second step of sintering is carried out at a high sintering temperature under the protection of an inert atmosphere, which can fully carbonize the resin powder. At the same time, the synergistic effect of g-C3N4 and the condition parameters of the second step of sintering promotes the carbonization of the resin powder, ensures the formation of more pseudo-graphite domains inside the hard carbon negative electrode material, and the pseudo-graphite domains are the most important structure for the storage of sodium ions in the hard carbon negative electrode material. The carbon layers are curved or turbulent, and the curved or turbulent graphitized carbon layers are stacked and connected to form a highly twisted structure and exhibit many nanopores, which can ensure more sodium ions to be stored in the carbon layers of the pseudo-graphite domains in the form of insertion, thereby improving the sodium storage capacity of the hard carbon negative electrode material and the cycle stability of the hard carbon negative electrode material. At the same time, g-C3N4 is completely decomposed at a high temperature of 1000℃ or above and escapes in the form of gas, avoiding the generation of impurity atoms in the hard carbon negative electrode material product. Finally, the hard carbon negative electrode material with pseudo-graphite structure and microporous structure is obtained.

[0012] Preferably, the mass ratio of the template agent to resorcinol is (1-2):(3-5), and the amount of the template agent can ensure the increase of the content of the microporous structure of the hard carbon negative electrode material. The microporous structure corresponds to the "micropore filling mechanism" of the sodium storage of the hard carbon material (i.e., the filling of sodium ions in the microporous structure). When the microporous structure inside the hard carbon material is more abundant, the sites for sodium storage are naturally more, which shows an increase in the reversible capacity of the sodium ion battery. Therefore, increasing the content of the microporous structure of the hard carbon negative electrode material can improve the storage capacity of sodium in the hard carbon negative electrode material, and further improve the reversible capacity of the hard carbon negative electrode material.

[0013] Preferably, the mass concentration of the ethanol aqueous solution is 50%-60%.

[0014] Preferably, the mass concentration of the formaldehyde solution is 40%-60%.

[0015] Preferably, the volume ratio of the ethanol aqueous solution and the formaldehyde solution is (2-4):1.

[0016] Preferably, the carbonate of alkali metal includes at least one of lithium carbonate, sodium bicarbonate or potassium carbonate; the carbonate of alkaline earth metal includes at least one of magnesium carbonate, calcium carbonate or barium carbonate. The addition of the above-mentioned carbonate of alkali metal template or carbonate of alkaline earth metal template, after sintering and acid washing, can obtain resin powder with more uniform pores. When different templates are selected, hard carbon negative electrode materials with different pore sizes can be obtained.

[0017] The above-mentioned templates can be decomposed into corresponding metal oxides and carbon dioxide under high-temperature calcination, and the escaped carbon dioxide can promote the preliminary formation of the internal microporous structure of the resin powder. After the metal oxides are dissolved by acid washing, a large number of microporous structures are exposed, forming resin powder with rich microporous structures.

[0018] Preferably, the reaction condition in S1 is to react at 60-80℃ for at least 1h.

[0019] When the reaction time is less than 1h in the preparation of the resin gel, the resin gel cannot be formed. The added template provides a matrix for the formation of the gel, i.e., the resin gel is formed by wrapping the calcium carbonate. This method can greatly shorten the time for the formation of the resin gel. Without the addition of the template, it takes about 7h to form the resin gel. After the addition of the template, the resin gel can be formed within 3h, which accelerates the formation of the resin gel and significantly improves the synthesis efficiency.

[0020] Preferably, the inert atmosphere in S2 is provided by any one of nitrogen, helium, argon or neon.

[0021] Preferably, before the temperature rising, the resin gel is further subjected to crushing, washing with clean water and drying at 60-80℃ to remove the unreacted reactants and organic solvents mixed in the resin gel.

[0022] Preferably, in S2, the acid washing is performed by using 1-2mol / L dilute acid, and after the acid washing, the resin powder is obtained by filtering and drying at 60-80℃; the dilute acid includes any one of dilute sulfuric acid, dilute hydrochloric acid or dilute nitric acid.

[0023] In the present application, since the metal oxide and the residual un-calcined template agent are embedded in the resin structure, 1-2 mol / L dilute acid can completely dissolve the metal oxide and the un-calcined template agent in the resin structure, so as to remove the embedded metal oxide and template agent in the resin structure and expose a large number of microporous structures. After volatilizing the acid at 60-80℃, the resin powder with rich microporous structure is obtained.

[0024] Preferably, the mass ratio of the resin powder to g-C3N4 in S3 is 4-1:1.

[0025] The above-mentioned ratio can promote the formation of a large number of pseudo-graphite domains in the hard carbon negative electrode material, thereby providing sufficient space for the storage of sodium ions in the hard carbon.

[0026] Preferably, the inert atmosphere in S4 is provided by any one of nitrogen, helium, argon or neon.

[0027] Preferably, the cooling is cooling to room temperature.

[0028] In a second aspect, the present application also provides the application of the hard carbon negative electrode material prepared by the above-mentioned preparation method in the preparation of battery negative electrode materials.

[0029] The battery prepared from the hard carbon negative electrode material of the present application has extremely high reversible capacity and excellent cycle stability, and has high market application value. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 The preparation method flow chart of the hard carbon negative electrode material of the present application;

[0031] Figure 2 The micropore characterization chart of the hard carbon negative electrode material with different amounts of CaCO3 template, wherein (a) is the N2 adsorption / desorption isotherm chart, and (b) is the micropore distribution chart;

[0032] Figure 3 The high-resolution transmission electron microscope image of the hard carbon negative electrode material according to Example 1 of the present application;

[0033] Figure 4 The high-resolution transmission electron microscope image of the hard carbon negative electrode material according to Comparative Example 1 of the present application;

[0034] Figure 5 The high-resolution transmission electron microscope image of the hard carbon negative electrode material according to Comparative Example 2 of the present application;

[0035] Figure 6 The performance test chart of the battery prepared from the hard carbon negative electrode material according to Example 1 of the present application, wherein (a) is the first two cycles of charge-discharge curves, and (b) is the 100-cycle cycle curve at a current density of 200 mA g -1 . DETAILED DESCRIPTION

[0036] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to specific examples. It should be understood that the specific examples described herein are merely intended to explain the present application and should not be used to limit the present application.

[0037] The method for preparing the hard carbon negative material in the conventional technology has the defects of complex process flow, low reversible capacity and poor cycle stability of the hard carbon negative material.

[0038] Therefore, the present application provides a method for preparing a hard carbon negative material for a sodium ion battery, which aims to prepare a hard carbon negative material with rich microstructure through a simple process. The hard carbon negative material obtained by the method has both a large amount of pseudo-graphite structure and rich microporous structure, and the above-mentioned structures promote the storage of sodium in the hard carbon negative material, and endow the hard carbon negative material with extremely high reversible capacity and excellent cycle stability.

[0039] Figure 1 The flow chart of the method for preparing the hard carbon negative material of the present application.

[0040] The g-C3N4 used in the following examples is prepared by sintering melamine, and the specific operation is as follows: 4g of melamine powder is taken in a ceramic crucible, and the crucible is placed in a muffle furnace, and heated to 550℃ at a heating rate of 2℃ / min, and kept for 5h, and after cooling to room temperature, the crucible is taken out, and the obtained yellow powder is g-C3N4.

[0041] The present application will be further described below with reference to specific examples, but it should not be understood as limiting the scope of protection of the present application.

[0042] Example 1

[0043] The present application provides a method for preparing a hard carbon negative material for a sodium ion battery, which comprises the following operations:

[0044] S1, 3g of resorcinol and 0.5g of calcium carbonate are taken in a beaker, 10ml of 50% ethanol aqueous solution is added and stirred uniformly, and then 5ml of 40% formaldehyde solution is added, and magnetic stirring is carried out at 60℃ and a rotation speed of 800r / min for 1h to obtain a resin gel;

[0045] S2, the resin gel is crushed into a fine particle state, repeatedly washed clean with clean water, filtered, dried at 60 DEG C, uniformly ground, then placed in a corundum boat and put into a tube sintering furnace for first-step sintering, helium gas is introduced as a protective gas, heated to 600 DEG C at a rate of 5 DEG C / min, after 1h of heat preservation roasting, the product is taken out, washed with 1 mol / L dilute hydrochloric acid until the calcium carbonate is completely removed, filtered, dried at 60 DEG C, and then a resin powder is obtained;

[0046] S3, the resin powder and g-C3N4 are mixed and ground at a mass ratio of 1:1 to obtain a uniform mixture powder;

[0047] S4, the mixture powder is again placed in a corundum boat and put into a tube sintering furnace for second-step sintering, argon gas is introduced as a protective gas, heated to 1200 DEG C at a rate of 5 DEG C / min, heat preserved for 2h, the product is taken out after the furnace body is cooled to room temperature, and a black powder is obtained as the hard carbon negative electrode material.

[0048] Example 2

[0049] The embodiment of the present application provides a preparation method of a hard carbon negative electrode material for a sodium ion battery, which comprises the following operations:

[0050] S1, 3g of resorcinol and 1g of calcium carbonate are taken in a beaker, 15ml of 55% ethanol aqueous solution is added and stirred uniformly, then 5ml of 50% formaldehyde solution is added, and magnetic stirring is carried out at 70 DEG C and a rotation speed of 750r / min for 2h to obtain a resin gel;

[0051] S2, the resin gel is crushed into a fine particle state, repeatedly washed clean with clean water, filtered, dried at 70 DEG C, uniformly ground, then placed in a corundum boat and put into a tube sintering furnace for first-step sintering, argon gas is introduced as a protective gas, heated to 700 DEG C at a rate of 8 DEG C / min, after 1.5h of heat preservation roasting, the product is taken out, washed with 1 mol / L dilute sulfuric acid until the calcium carbonate is completely removed, filtered, dried at 70 DEG C, and then a resin powder is obtained;

[0052] S3, the resin powder and g-C3N4 are mixed and ground at a mass ratio of 1:1 to obtain a uniform mixture powder;

[0053] S4, the mixture powder is again placed in a corundum boat and put into a tube sintering furnace for second-step sintering, argon gas is introduced as a protective gas, heated to 1300 DEG C at a rate of 8 DEG C / min, heat preserved for 2.5h, the product is taken out after the furnace body is cooled to room temperature, and a black powder is obtained as the hard carbon negative electrode material.

[0054] Example 3

[0055] The embodiment of the present application provides a preparation method of a hard carbon negative electrode material for a sodium ion battery, which comprises the following operations:

[0056] S1, take 4g resorcinol, 1.5g calcium carbonate in a beaker, add 15ml 55% ethanol solution and stir evenly, then add 5ml 50% formaldehyde solution, under the condition of 70℃ and 750r / min, magnetic stirring for 2h to obtain resin gel;

[0057] S2, the resin gel is crushed into fine particles, washed repeatedly with clean water, filtered, dried at 70℃, ground uniformly, then placed in a corundum boat and put into a tube sintering furnace for first step sintering, neon gas is introduced as protective gas, heated to 700℃ at a rate of 8℃ / min, and kept for 1.5h, then taken out, washed with 1mol / L dilute sulfuric acid until the calcium carbonate is completely removed, filtered, dried at 70℃, and then resin powder is obtained;

[0058] S3, the resin powder and g-C3N4 are mixed and ground according to a mass ratio of 3:1 to obtain a uniform mixture powder;

[0059] S4, the mixture powder is placed in a corundum boat and put into a tube sintering furnace for second step sintering, neon gas is introduced as protective gas, heated to 1300℃ at a rate of 8℃ / min, and kept for 2.5h, then taken out after the furnace body is cooled to room temperature, and black powder is obtained, which is a hard carbon negative electrode material.

[0060] Example 4

[0061] The embodiment of the present application provides a preparation method of a hard carbon negative electrode material for a sodium ion battery, which comprises the following operations:

[0062] S1, take 5g resorcinol, 2g calcium carbonate in a beaker, add 20ml 60% ethanol solution and stir evenly, then add 5ml 60% formaldehyde solution, under the condition of 80℃ and 800r / min, magnetic stirring for 3h to obtain resin gel;

[0063] S2, the resin gel is crushed into fine particles, washed repeatedly with clean water, filtered, dried at 80℃, ground uniformly, then placed in a corundum boat and put into a tube sintering furnace for first step sintering, neon gas is introduced as protective gas, heated to 800℃ at a rate of 10℃ / min, and kept for 2h, then taken out, washed with 1mol / L dilute nitric acid until the calcium carbonate is completely removed, filtered, dried at 80℃, and then resin powder is obtained;

[0064] S3, the resin powder and g-C3N4 are mixed and ground according to a mass ratio of 4:1 to obtain a uniform mixture powder;

[0065] S4, the mixed powder is put into a corundum boat and placed in a tube sintering furnace for second-step sintering, neon gas is introduced as a protective gas, the temperature is raised to 1500℃ at a rate of 10℃ / min, and the temperature is kept for 3h, the furnace is cooled to room temperature, and then the black powder is taken out, which is a hard carbon negative electrode material.

[0066] Comparative Example 1

[0067] Compared with Example 1, no calcium carbonate is added, and the rest is the same as Example 1.

[0068] Comparative Example 2

[0069] Compared with Example 2, no g-C3N4 is added, and the rest is the same as Example 2.

[0070] Comparative Example 3

[0071] Commercial hard carbon negative electrode material of sodium ion battery.

[0072] Effect Example 1

[0073] 1) The micropore characterization of the hard carbon negative electrode material with different amounts of CaCO3 template is shown in the following table: Figure 2 .

[0074] Figure 2 The micropore characterization graphs of the hard carbon negative electrode material with different amounts of CaCO3 template, wherein (a) is the N2 adsorption / desorption isotherm graph, and (b) is the micropore distribution graph;

[0075] Figure 2 (a) The curve is the N2 adsorption / desorption isotherm, each calcium carbonate content corresponds to one adsorption and one desorption, Figure 2 (a) It can be seen that the N2 adsorption / desorption isotherm and the micropore distribution graph show a typical type I curve, which indicates that the sample (hard carbon negative electrode material) contains micropores inside. From Figure 2 b, it can be seen that the vertical coordinate corresponding to each group of samples is obviously larger near the horizontal coordinate of 0.6nm, indicating that the strength of the micropore structure near 0.6nm is obviously the strongest, and the greater the strength, the more micropores in the sample, and it indicates that the micropore size is mainly concentrated in 0.5nm-0.7nm Figure 2 b), and it also indicates that the amount of CaCO3 template has a relatively obvious effect on the micropore content inside the sample. When no CaCO3 is added, the number of micropores is significantly lower than that of the sample with 1g CaCO3 template and the sample with 2g CaCO3 template, and from Figure 2 b, it can be seen that the micropore content increases with the increase of the amount of CaCO3 template added.

[0076] 2) The microstructure of the hard carbon negative electrode material samples of Example 1 and Comparative Examples 1-2 was observed by high-resolution transmission electron microscopy. Figures 3-5 shown.

[0077] Figure 3 This is a high-resolution transmission electron microscope image of the hard carbon negative electrode material according to Example 1 of the present invention;

[0078] from Figure 3 It can be seen that the hard carbon negative electrode material of Example 1 has a large number of layered structures, namely pseudo-graphite areas, and the sample (hard carbon negative electrode material) also has abundant microporous structures wrapped by carbon layers (indicated by circles).

[0079] Figure 4 This is a high-resolution transmission electron microscope image of the hard carbon negative electrode material according to Comparative Example 1 of the present invention;

[0080] from Figure 4 It can be seen that the internal microstructure of the hard carbon negative electrode material of Comparative Example 1 (does not contain calcium carbonate) is mainly composed of stacked carbon layers, and there is no microporous structure. This shows that the CaCO3 template plays a key and indispensable role in the formation of micropores inside the hard carbon negative electrode material.

[0081] Figure 5 This is a high-resolution transmission electron microscope image of the hard carbon negative electrode material according to Comparative Example 2 of the present invention;

[0082] from Figure 5 As can be seen, the internal layered structure of the hard carbon negative electrode material in Comparative Example 2 is not obvious, which indicates that the pseudo-graphite region inside the hard carbon negative electrode material is significantly less. Therefore, Comparative Example 2 can prove that the addition of g-C3N4 can promote the improvement of the pseudo-graphitization degree of the hard carbon negative electrode material.

[0083] Effect Example 2

[0084] The hard carbon negative electrode materials obtained in Examples 1-4 and Comparative Examples 1-3 were used to prepare batteries, and the battery performance was tested. The results are shown in Table 1.

[0085] Table 1

[0086]

[0087] The above tests in Table 1 show that the electrode materials of Examples 1-4 have excellent electrochemical properties, while the electrochemical properties of Comparative Examples 1-3, such as the first-cycle discharge capacity, the first-cycle charge capacity, the first coulombic efficiency (ICE), and the capacity retention rate after 5000 cycles, are all inferior to those of Examples 1-4. This indicates that the addition of g-C3N4 and CaCO3 templates in the present invention can promote the formation of pseudo-graphite structure and microporous structure in the hard carbon negative electrode material.

[0088] Figure 6The performance test chart of the battery prepared from the hard carbon negative material according to Embodiment 1 of the present application, wherein (a) is the charge-discharge curve of the first two circles, (b) is the 100-cycle cycle curve at a current density of 200 mA g -1

[0089] From Figure 6 the charge-discharge curve of (a) and Figure 6 the cycle curve of (b), it can be seen that the battery prepared from the hard carbon negative material of Embodiment 1 has excellent reversible capacity and excellent cycle stability.

[0090] This shows that the pseudo-graphite structure and the microporous structure in the hard carbon negative material of the present application increase the storage of sodium in the hard carbon negative material, improve the "micropore filling" sodium storage mode of the hard carbon negative material, and improve the reversible capacity and cycle stability of the hard carbon negative material, and thus a sodium ion battery with excellent electrochemical performance can be obtained.

[0091] The above merely describes preferred embodiments of the present application but should not be used to restrict the present application, and any modification, equivalent replacement or improvement made within the spirit and principle of the present application should be included in the protection scope of the present application.​

Claims

1. A method for preparing a hard carbon anode material for a sodium-ion battery, characterized in that, The method comprises the following steps: S1, mixing resorcinol, a template agent and an ethanol aqueous solution uniformly, then adding a formaldehyde solution to obtain a resin gel through reaction; S2, in an inert atmosphere, heating the resin gel to 600-800℃ at a heating rate of 5-10℃ / min, keeping the temperature for 1-2h, then taking out the resin gel, acid washing and drying to obtain a resin powder; S3, mixing and grinding the resin powder with g-C3N4 to obtain a mixed powder; S4, in an inert atmosphere, heating the mixed powder to 1200-1500℃ at a heating rate of 5-10℃ / min, keeping the temperature for 2-3h, and cooling to obtain the hard carbon negative electrode material.

2. The production method according to claim 1, characterized by, The mass ratio of the template agent to resorcinol is (1-2):(3-5); and / or The mass concentration of the ethanol aqueous solution is 50%-60%; and / or The mass concentration of the formaldehyde solution is 40%-60%; and / or The volume ratio of the ethanol aqueous solution to the formaldehyde solution is (2-4):

1.

3. The preparation method according to claim 1, characterized in that The carbonate of alkali metal includes at least one of lithium carbonate, sodium bicarbonate or potassium carbonate; and the carbonate of alkali earth metal includes at least one of magnesium carbonate, calcium carbonate or barium carbonate.

4. The method of claim 1, wherein, The reaction condition in S1 is to react at 60-80℃ for at least 1h.

5. The preparation method according to claim 1, characterized in that The inert atmosphere in S2 is provided by any one of nitrogen, helium, argon or neon; and / or Before heating, the resin gel further comprises crushing, washing with water and drying at 60-80℃.

6. The method of claim 1, wherein, The acid washing in S2 adopts dilute acid washing with a concentration of 1-2mol / L, and the resin powder is obtained through filtering and drying at 60-80℃ after acid washing.

7. The production method according to claim 6, wherein The dilute acid includes any one of dilute sulfuric acid, dilute hydrochloric acid or dilute nitric acid.

8. The method of claim 1, wherein, The mass ratio of the resin powder to g-C3N4 in S3 is 4-1:

1.

9. The method of claim 1, wherein, The inert atmosphere in S4 is provided by any one of nitrogen, helium, argon or neon; and / or The cooling is cooling to room temperature.

10. Application of the hard carbon negative electrode material prepared by the preparation method in any one of claims 1-9 in preparation of a battery negative electrode material.

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