Sodium ion battery negative electrode hard carbon material and preparation method and application thereof

Abstract

The invention provides a preparation method and application of sodium-ion battery negative electrode hard carbon, and the preparation method of the sodium-ion battery negative electrode hard carbon comprises the following steps: mixing a starch raw material and organic zinc, and carrying out two-stage pre-oxidation heat treatment in an oxygen-containing atmosphere. And then adding organic acid into the ground material, carrying out third-stage heat treatment in a protective atmosphere, and slowly cooling by adopting an annealing process. By adding the organic zinc material, the thermal stability of starch pre-carbonization can be improved, the effect of inhibiting expansion of the starch is achieved, the problem of structural damage caused by expansion due to the characteristics of starch raw materials is solved, zinc oxide generated by organic zinc pyrolysis in the pre-oxidation process serves as a template, a large number of mesopores are provided for the finally prepared hard carbon material, and sodium storage sites of the hard carbon material are increased; and the organic acid is added to dissolve the zinc oxide so that the zinc oxide can be more uniformly distributed in the hard carbon precursor, the pore structure of the hard carbon is stabilized by adding the organic acid, and the prepared hard carbon shows relatively high first coulombic efficiency and reversible specific capacity and is good in rate capability.

Description

Technical Field

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

[0002] Lithium-ion batteries dominate in the fields of consumer electronics and electric vehicles. However, large-scale lithium-based energy storage technologies have problems such as poor safety, poor low-temperature performance, and high costs. Sodium-ion batteries have a similar working principle to lithium-ion batteries, both being secondary rocking-chair type rechargeable batteries, and with the advantages of high abundance of sodium ions and low overall cost, they have become a useful supplement to the new generation of energy storage technologies. However, due to the essential differences between sodium ions and lithium ions, namely the larger ionic radius of sodium ions and the lower sodium-graphite intercalation thermodynamic stability, the graphite negative electrode that is maturely used in lithium-ion batteries cannot effectively be used as a sodium storage negative electrode material. Therefore, it is necessary to develop new sodium storage negative electrode materials for sodium-ion battery technology.

[0003] Hard carbon has the characteristics of disordered internal crystal arrangement and large interlayer spacing. It can store more charges under the same volume, and is conducive to the deintercalation and intercalation of Na+. Moreover, the precursors for synthesizing hard carbon have multiple sources and low costs, and are considered potential negative electrode materials for sodium-ion batteries, and have been widely studied in recent years. However, the complex raw material sources of hard carbon materials result in unfixed process routes, which to a certain extent restrict the development of sodium-ion batteries. Starch is one of the most abundant renewable biomaterials, with simple composition, high carbon content, and low cost, and is an excellent precursor for producing hard carbon. However, directly carbonizing starch usually results in a puffing phenomenon, losing its original near-spherical morphology. The obtained hard carbon has a large specific surface area, low initial Coulomb efficiency, low sodium storage capacity, and greatly occupies the production space, reducing production efficiency. It is not conducive to industrial production. When starch without stabilization treatment is heated to about 300 °C, due to the overlapping effect of the starch softening and dehydration processes, the starch granules are prone to foaming and fusing phenomena, thus forming an extremely fluffy foamed carbon material, losing its original near-spherical morphology, and greatly occupying the production space. In the past, a method of maintaining the temperature at 200-250 °C for more than 20 h in an air atmosphere was used to promote starch dehydration, so as to ensure that the starch does not foam and expand during high-temperature carbonization. However, this method takes too long and seriously affects industrial production efficiency. The method of adding cross-linking agents, metal oxides, dehydrating agents, and oxidizing agents can reduce the time for starch stabilization treatment to a certain extent, but such methods have high costs, complex processes, and are not conducive to the preparation of large-scale starch-based hard carbon. And the low initial charge-discharge efficiency of hard carbon is also a problem that needs to be solved.

[0004] In view of this, the present invention is specifically proposed. Summary of the Invention

[0005] The first object of the present invention is to provide a method for preparing a hard carbon material for the negative electrode of a sodium-ion battery. This method solves the problem of structural damage caused by expansion due to the characteristics of the starch raw material by mixing organic zinc and starch for two-stage pre-oxidation heat treatment, adding an appropriate amount of organic acid, and then performing one-stage heat treatment in an atmosphere.

[0006] The second object of the present invention is to provide a hard carbon material for the negative electrode of a sodium-ion battery prepared by the above preparation method. The hard carbon material obtained after adopting the solution of the present invention has a high capacity, a high first charge-discharge efficiency, and good rate performance.

[0007] In order to achieve the above objects of the present invention, the following technical solutions are specifically adopted:

[0008] The present invention provides a method for preparing a hard carbon material for the negative electrode of a sodium-ion battery, comprising the following steps:

[0009] First, pre-oxidize organic zinc and starch in an oxygen-containing atmosphere for a short time at a relatively low temperature in the first stage, then pre-oxidize in the oxygen-containing atmosphere for a longer time at a relatively high temperature in the second stage, and finally perform a third-stage high-temperature heat treatment and annealing treatment in a protective atmosphere, wherein the organic zinc is any one or a mixture of several of zinc gluconate, methyl zinc, zinc citrate, zinc acetate, zinc lactate, and zinc glycinate. The starch includes at least one of biomass starches such as oxidized starch, hydroxypropyl starch, corn starch, potato starch, rice starch, and mung bean starch.

[0010] Preferably, the protective atmosphere used is at least one of argon and nitrogen.

[0011] The reason for first mixing and pre-oxidizing organic zinc and starch in the solution of the present invention is to enhance the oxygen-containing functional groups during carbonization, effectively increase the thermal stability of pre-carbonized starch, and achieve the effect of inhibiting its expansion. In this way, the problem of starch foaming can be solved, and the physical and chemical structural characteristics of the starch-based material can be optimized to solve problems such as low capacity caused by structural damage due to the characteristics of the starch raw material.

[0012] Immediately afterwards, grinding the treated material and then adding an organic acid is to dissolve the zinc oxide generated by the pyrolysis of organic zinc during the pre-oxidation process as a template and make it more uniformly distributed in the hard carbon precursor. And the addition of the organic acid stabilizes the pore structure of the hard carbon. It improves the storage capacity and transmission path of sodium ions, and a high-performance starch-based hard carbon material can be prepared.

[0013] The reason why the two-stage heat treatment method can solve the problem of starch foaming is as follows: During the heat treatment in air, good gas discharge channels can be constructed inside the starch, which helps the timely discharge of water vapor during the carbonization of starch, avoids starch gelatinization, and inhibits the foaming phenomenon. Organic zinc is rich in oxygen functional groups, and zinc oxide generated during the pyrolysis of organic zinc can change the physicochemical properties of the mixture, absorb the heat accumulated inside the starch, control the temperature difference between the inside and outside of the starch, avoid local overheating and local foaming, and effectively increase the thermal stability of starch. The second-stage heat treatment carbonizes and completely pre-oxidizes the starch. Therefore, the combination of the two-stage heat treatment method finally achieves the effects of inhibiting starch foaming and increasing stability.

[0014] The thermal decomposition temperature of starch is between 200 and 260 °C. If the temperature is too low, the pre-oxidation is incomplete; if the temperature is too high, the starch inhibition strategy fails. Therefore, it is necessary to control within a suitable temperature range.

[0015] The temperature of the first-stage heat treatment for pre-oxidation is 190 - 300 °C, preferably 220 - 300 °C;

[0016] Preferably, the heating rate of the carbonization is 1 - 4 °C / min.

[0017] Preferably, the time of the first-stage heat treatment is 0.5 - 10 h, preferably 0.5 - 6 h;

[0018] The temperature of the second-stage heat treatment for pre-oxidation is 180 - 300 °C, preferably 230 - 300 °C;

[0019] Preferably, the time of the second-stage heat treatment is 2 - 15 h, preferably 4 - 12 h;

[0020] Preferably, the heating rate of the second-stage heat treatment is 2 - 10 °C / min.

[0021] The third-stage heat treatment is carried out in two stages. The first stage is the heating and holding process: the temperature of the heat treatment in a protective atmosphere in the third stage is 1200 - 1600 °C, the holding time is 1 - 10 h, and the heating rate is 1 - 10 °C / min. The atmosphere is one or more of argon and nitrogen. The second stage is the annealing treatment.

[0022] The reason why the third-stage heat treatment is carried out in two stages is that the temperature in the first stage achieves the purpose of pyrolytic carbonization, and from the second-stage annealing operation, the holding time in the first stage can be reduced and the structure can be made more stable.

[0023] Preferably, the co-preoxidation raw material includes at least one. The co-preoxidation of starch materials of the same kind ensures the uniformity and stability of the final material, can optimize the physical and chemical structural characteristics of the starch-based material, improve the storage capacity and transmission path of sodium ions, reduce the heat treatment time and optimize the cost, and can prepare high-performance starch-based hard carbon materials.

[0024] Preferably, in the mixed raw material, the content of the co-preoxidation raw material is 10-50 wt%, preferably 10-30 wt%.

[0025] Preferably, the content of oxygen in the oxygen-containing atmosphere is above 10 v%, preferably at least one of a mixture of oxygen, air, a mixture of oxygen-diluent gas, and a mixture of air-diluent gas;

[0026] Preferably, the diluent gas includes at least one of nitrogen and inert gas.

[0027] Preferably, the added organic acid includes citric acid, malic acid, tartaric acid, acetic acid, succinic acid, oxalic acid, phytic acid.

[0028] The present invention also provides a hard carbon material for the negative electrode of a sodium ion battery prepared by the above preparation method;

[0029] Preferably, in the hard carbon material for the negative electrode, the content of the starch-based negative electrode active material is above 50 wt%, more preferably, the content of the negative electrode active material is above 60 wt%, and further 70-90 wt%.

[0030] The hard carbon material for the negative electrode of a sodium ion battery prepared by the above preparation method of the present invention has good application in equipment drive.

[0031] The solution of the present invention is based on the above method of adding organic zinc carbonization + organic acid three-stage heat treatment, which can solve the foaming problem faced by the heat treatment of starch raw materials, provide a more uniformly distributed template, improve the capacity and initial efficiency of starch-based hard carbon, and has better technical effects. Description of the Drawings

[0032] Figure 1 It is the material after pre-oxidation in Example 1;

[0033] Figure 2 It is the SEM image of the material prepared in Example 1;

[0034] Figure 3 It is the SEM image of the material prepared in Example 2;

[0035] Figure 4 It is the charge-discharge curve of the material prepared in Example 1;

[0036] Figure 5 It is the rate performance graph of the material prepared in Example 1. Detailed implementation manners

[0037] The following will describe in detail the implementation scheme of the present invention in combination with embodiments. However, those skilled in the art will understand that the following embodiments are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. For those not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. For reagents or instruments whose manufacturers are not specified, they are all conventional products that can be obtained through commercial purchase.

[0038] Example 1

[0039] Step (1): Mix organic zinc with starch.

[0040] Mix zinc gluconate and corn starch in a mass ratio of 1:4 and add them to a stirring device for uniform stirring to obtain a premix.

[0041] Step (2): First-stage heat treatment.

[0042] Place the premix in a low-temperature sintering furnace. In an air (oxygen-containing atmosphere) environment, heat it up to 230 °C (marked as T1) at a heating rate of 2 °C / min, and keep it warm for 0.5 h. After the heat preservation ends, a pre-oxidized mixture (first-stage material) is obtained.

[0043] Step (3): Second-stage heat treatment.

[0044] Put the first-stage material into a low-temperature sintering furnace. In an air (oxygen-containing atmosphere) environment, heat it up to 250 °C (marked as T2) at a heating rate of 5 °C / min, and keep it warm for 6 h. After the heat preservation ends, a pre-oxidized mixture (second-stage material) is obtained.

[0045] Step (4): Add organic acid.

[0046] Add acetic acid solution to the pre-oxidized mixture (second-stage material) until it is completely wet

[0047] Step (5): Third-stage heat treatment.

[0048] After step 4, heat the second-stage material to 1520 °C (marked as T3) at a rate of 5 °C / min and keep it warm for 2 h, then cool it down to 800 °C at a rate of 2 °C / min, and then cool it naturally. Then grind and disperse the material to obtain a hard carbon negative electrode material.

[0049] Example 2

[0050] Step (1): Mix organic zinc with starch.

[0051] Mix zinc gluconate and potato starch in a mass ratio of 1:4 and add them to a stirring device for uniform stirring to obtain a premix.

[0052] Step (2): The first heat treatment.

[0053] Place the premix in a low-temperature sintering furnace. In an air (oxygen-containing atmosphere) environment, heat it up to 230 °C (marked as T1) at a heating rate of 2 °C / min, hold for 0.5 h, and after the holding is completed, obtain a pre-oxidized mixture (the first-stage material).

[0054] Step (3): The second heat treatment.

[0055] Put the first-stage material into a low-temperature sintering furnace. In an air (oxygen-containing atmosphere) environment, heat it up to 250 °C (marked as T2) at a heating rate of 5 °C / min, hold for 6 h, and after the holding is completed, obtain a pre-oxidized mixture (the second-stage material).

[0056] Step (4): Add organic acid.

[0057] Add the citric acid solution to the pre-oxidized mixture (the second-stage material) until it is completely wet.

[0058] Step (5): The third heat treatment.

[0059] After Step 4, heat the second-stage material to 1520 °C (marked as T3) at a rate of 5 °C / min and hold for 2 h, then cool it to 800 °C at a rate of 2 °C / min, and then cool it naturally. Then grind and disperse the material to obtain a hard carbon anode material.

[0060] Example 3

[0061] Step (1): Mix organic zinc with starch.

[0062] Mix zinc citrate and corn starch in a mass ratio of 1:4 and add them to a stirring device to stir evenly to obtain a premix.

[0063] Step (2): The first heat treatment.

[0064] Place the premix in a low-temperature sintering furnace. In an air (oxygen-containing atmosphere) environment, heat it up to 230 °C (marked as T1) at a heating rate of 2 °C / min, hold for 0.5 h, and after the holding is completed, obtain a pre-oxidized mixture (the first-stage material).

[0065] Step (3): The second heat treatment.

[0066] Put the first-stage material into a low-temperature sintering furnace. In an air (oxygen-containing atmosphere) environment, heat it up to 250 °C (marked as T2) at a heating rate of 5 °C / min, hold for 6 h, and after the holding is completed, obtain a pre-oxidized mixture (the second-stage material) Figure 1 It can be seen that no expansion occurs.

[0067] Step (4): Add organic acid.

[0068] Add acetic acid solution to the pre-oxidized mixture (second-stage material) until it is completely wetted.

[0069] Step (5): Third-stage heat treatment.

[0070] After Step 4, heat the second-stage material to 1520 °C (marked as T3) at a rate of 5 °C / min and hold for 2 h, then cool at a rate of 2 °C / min to 800 °C, and then cool naturally. Then grind and disperse the material to obtain the hard carbon anode material ( Figure 3 ).

[0071] Comparative Example 1

[0072] Step (1): Pre-carbonization.

[0073] Place corn starch in a muffle furnace and heat it to 230 °C (marked as T1) at a heating rate of 2 °C / min and hold for 6 h. After the holding is completed, a pre-oxidized product is obtained. Under this condition, the product expands severely during oxidation.

[0074] Step (2): Add organic acid.

[0075] Add citric acid solution to the pre-oxidized mixture (second-stage material) until it is completely wetted.

[0076] Step (3): Second-stage heat treatment.

[0077] After Step 2, heat the pre-carbonized material to 1520 °C (marked as T2) at a rate of 5 °C / min and hold for 2 h, then cool at a rate of 2 °C / min to 800 °C, and then cool naturally. Then grind and disperse the material to obtain the hard carbon anode material. The SEM image is shown in Figure 2 .

[0078] Comparative Example 2

[0079] Step (1): Mix organic zinc and starch.

[0080] Mix zinc gluconate and corn starch in a mass ratio of 1:4 and add them to a stirring device for uniform stirring to obtain a pre-mixture.

[0081] Step (2): First-stage heat treatment.

[0082] Place the pre-mixture in a low-temperature sintering furnace. In an air (oxygen-containing atmosphere) environment, heat it to 230 °C (marked as T1) at a heating rate of 2 °C / min and hold for 0.5 h. After the holding is completed, a pre-oxidized mixture (first-stage material) is obtained.

[0083] Step (3): Second-stage heat treatment.

[0084] Put a section of material into a low-temperature sintering furnace. In an air (oxygen-containing atmosphere) environment, heat it up to 250 °C (marked as T2) at a heating rate of 5 °C / min, hold for 6 h, and obtain a pre-oxidized mixture (two-section material) after the holding ends.

[0085] Step (4): Third-stage heat treatment.

[0086] After Step 3, heat the pre-carbonized material to 1520 °C (marked as T3) at a rate of 5 °C / min and hold for 2 h, then cool it at a rate of 2 °C / min to 800 °C, and then cool it naturally. Then grind and disperse the material to obtain a hard carbon anode material.

[0087] Comparative Example 3:

[0088] Example 1

[0089] Step (1): Mix organic zinc and starch.

[0090] Mix zinc gluconate and corn starch in a mass ratio of 1:4 and add them to a stirring device to stir evenly to obtain a pre-mixture.

[0091] Step (2): First-stage heat treatment.

[0092] Place the pre-mixture in a low-temperature sintering furnace. In an air (oxygen-containing atmosphere) environment, heat it up to 230 °C (marked as T1) at a heating rate of 2 °C / min, hold for 0.5 h, and obtain a pre-oxidized mixture (one-section material) after the holding ends.

[0093] Step (3): Second-stage heat treatment.

[0094] Put the one-section material into a low-temperature sintering furnace. In an air (oxygen-containing atmosphere) environment, heat it up to 250 °C (marked as T2) at a heating rate of 5 °C / min, hold for 6 h, and obtain a pre-oxidized mixture (two-section material) after the holding ends.

[0095] Step (4): Add organic acid.

[0096] Add acetic acid solution to the pre-oxidized mixture (two-section material) until it is completely wet.

[0097] Step (5): Third-stage heat treatment.

[0098] After Step 4, heat the two-section material to 1520 °C (marked as T3) at a rate of 5 °C / min and hold for 2 h, and then cool it naturally. Then grind and disperse the material to obtain a hard carbon anode material.

[0099] Experimental Example 1

[0100] Electrochemical test:

[0101] The prepared hard carbon anode materials (materials prepared in Example 1 and Comparative Examples 1-3), conductive carbon (super-p), and sodium carboxymethyl cellulose (CMC) were dissolved in deionized water at a mass ratio of 9:0.5:0.5 to form a uniform slurry. The slurry was evenly coated on an aluminum foil current collector and then placed in a drying oven at 120 °C for 12 h to obtain a hard carbon electrode sheet.

[0102] The hard carbon electrode sheet was punched into a disk with a diameter of 10 mm. A sodium metal sheet was used as the negative electrode side, and the hard carbon electrode sheet was used as the positive electrode side. The electrolyte was 1 M NaPF6 in diglyme. A CR2025 coin cell was assembled in a glove box filled with an argon atmosphere. The battery was subjected to electrochemical performance testing at a current density of 30 mA / g and a voltage range of 0.01-3 V. Table 1 shows the electrochemical performance parameters of the hard carbon synthesized under different conditions. It can be seen from Table 1 that the reversible capacity and the first charge-discharge efficiency of the hard carbon prepared by adding organic zinc and organic acid have been greatly improved. In Comparative Example 1, no co-preoxidation raw materials were added. In Comparative Example 2, no organic acid was added. In the third heat treatment stage of Comparative Example 3, there was no annealing treatment, so the effects could not meet the expectations.

[0103]

[0104] Table 1 Electrochemical parameter diagram of the hard carbon synthesized in the examples and comparative examples.

Claims

1. A preparation method of a hard carbon material for the negative electrode of a sodium-ion battery, characterized in that, It includes the following steps: First, mix the organozinc material with starch to form a mixed raw material, conduct two-stage heat treatment in an oxygen-containing atmosphere, then add an organic acid, and then conduct the third-stage heat treatment in a protective atmosphere.

2. The preparation method according to claim 1, characterized in that, The temperature of the first-stage heat treatment for pre-oxidation is 190 - 300 °C, the heating rate of carbonization is 1 - 4 °C / min, and the time of the first-stage heat treatment is 0.5 - 10 h.

3. The preparation method according to claim 2, characterized in that, The temperature of the first-stage heat treatment for pre-oxidation is 220 - 300 °C; the time of the first-stage heat treatment is 0.5 - 6 h; the temperature of the second-stage heat treatment for pre-oxidation is 180 - 300 °C, the time of the second-stage heat treatment is 2 - 15 h, and the heating rate of the second-stage heat treatment is 2 - 10 °C / min; the temperature of the second-stage heat treatment for pre-oxidation is 230 - 300 °C; the time of the second-stage heat treatment is 4 - 12 h.

4. The preparation method according to claim 1, wherein The added organic acids include citric acid, malic acid, tartaric acid, acetic acid, succinic acid, oxalic acid, and phytic acid.

5. The preparation method according to claim 1, wherein, The temperature of the heat treatment in the third-stage protective atmosphere is 1200 - 1600 °C, the holding time is 1 - 10 h, and the heating rate is 1 - 10 °C / min.

6. The preparation method according to claim 5, characterized in that, The starch includes at least one of oxidized starch, hydroxypropyl starch, corn starch, potato starch, rice starch, and mung bean starch; The starch in the mixed raw material includes one or more of corn starch, cassava starch, potato starch, rice starch, wheat starch, and mung bean starch.

7. The preparation method according to claim 6, characterized in that, In the mixed raw material, the content of organozinc is 10 - 50 wt%; the content of oxygen is above 10 v%, and the oxygen-containing atmosphere includes at least one of a mixture of oxygen, air, a mixture of oxygen - diluent gas, and a mixture of air - diluent gas; the diluent gas includes at least one of carbon dioxide gas, nitrogen gas, and inert gas.

8. The hard carbon material for the negative electrode of a sodium-ion battery prepared by the preparation method according to claim 1; characterized in that, In the negative hard carbon material, the content of the starch-based negative active material is above 50 wt%.

9. The hard carbon material for the negative electrode of a sodium-ion battery according to claim 8, wherein The content of the negative active material is 70 - 90 wt%.

10. Application of a negative hard carbon material for a sodium-ion battery and its preparation method in equipment drive.

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