Negative electrode material, preparation method thereof and application of negative electrode material in preparation of special-shaped battery

Abstract

The invention relates to a negative electrode material, a preparation method thereof and application of the negative electrode material in preparation of a special-shaped battery, and belongs to the technical field of battery materials. The preparation method comprises the following steps: firstly carrying out formylation modification on bamboo fibers, then carrying out a Schiff base reaction, introducing carboxylic acid lithium salt by utilizing C = N bond chemical bonding, and finally carrying out an in-situ reaction by utilizing isopropyl titanate and carboxylic acid lithium salt chemically bonded and grafted to the tail ends of the bamboo fibers, so as to form the lithium titanate active negative electrode material. The lithium carboxylate is bonded on the surface of the bamboo fiber through a chemical bond, can be better and uniformly dispersed on the surface of the bamboo fiber when reacting with isopropyl titanate, and is tightly attached to the bamboo fiber, so that after carbonization treatment, a carbon material formed by the bamboo fiber and a lithium titanate active negative electrode material can be better and tightly compounded, and the lithium titanate active negative electrode material can be more tightly compounded. And the carbon material and the lithium titanate active negative electrode material are dispersed more uniformly and play a better synergistic effect, so that the charge transfer resistance is reduced, and the initial coulombic efficiency, the first discharge capacity and the cycle stability are improved.

Description

Technical Field

[0001] The present invention relates to a negative electrode material, a preparation method thereof, and an application in the preparation of special-shaped batteries, belonging to the technical field of battery materials. Background Art

[0002] Lithium-ion batteries, with their advantages such as high specific energy and high specific power, have become the most frequently used mobile power sources for the general public in daily life, such as electronic and mechanical products like drones and electronic watches. General square lithium-ion batteries already have relatively mature research and applications in the existing processing market, with a high level of automation and can be processed by winding the electrode sheets. However, in wearable devices such as smart watches, the batteries assembled in different models have different specifications and standards. Such batteries cannot be processed by winding the electrode sheets, so they are classified as special-shaped lithium-ion batteries. The production process of special-shaped lithium-ion batteries requires several major processes such as electrode sheet coating, electrode sheet punching, electrode sheet bag making, electrode sheet stacking and welding, vacuum liquid injection, and formation. In addition, due to the small size, light weight, and limited power of the power source carried by micro-drones, the flight time and service efficiency are restricted. Shaping the lithium-ion battery into a special shape and conforming it to the fuselage can achieve the integration of load-bearing and power supply, and achieve the goals of further weight reduction, space saving, and improved endurance of the drone.

[0003] Therefore, with the rapid development of electronic and mechanical products such as drones and electronic watches, the demand for special-shaped lithium-ion batteries is gradually increasing. However, due to the miniaturization of volume and weight and the requirements for the service life of electronic and mechanical products, the discharge capacity and cycle performance of lithium-ion batteries can no longer meet the current development needs of special-shaped lithium-ion batteries. Among them, the negative electrode material used in the battery most restricts the overall performance of the lithium-ion battery. Therefore, it is necessary to develop a negative electrode material to meet the usage requirements of lithium-ion batteries in the field of special-shaped batteries. Summary of the Invention

[0004] The purpose of the present invention is to provide a negative electrode material, a preparation method thereof, and an application in the preparation of special-shaped batteries to meet the usage requirements of lithium-ion batteries in the field of special-shaped batteries.

[0005] The present invention provides a preparation method of a negative electrode material, comprising the following steps:

[0006] (1) Mix bamboo fiber and water and then perform steam explosion treatment to obtain pretreated bamboo fiber; the steam pressure during the steam explosion treatment is 1.8 - 1.9 MPa;

[0007] (2) React the pretreated bamboo fiber with periodate in an acidic environment to obtain aldehyde-grouped bamboo fiber;

[0008] (3) Perform a Schiff base reaction between the aldehyde groups in the aldehyde-functionalized bamboo fibers and the amino groups in lithium amino acid to obtain lithium salt grafted bamboo fibers; lithium amino acid is prepared by reacting 3-aminopropanesulfonic acid or 6-aminohexanoic acid with lithium hydroxide;

[0009] (4) After dropping the mixed solution into the dispersion of lithium salt grafted bamboo fibers, heat it to 130 - 150 °C and carry out a mixed reaction to obtain bamboo fibers with in-situ grown lithium titanate; the mixed solution is prepared by mixing isopropyl titanate and ethanol;

[0010] (5) Carbonize the bamboo fibers with in-situ grown lithium titanate to obtain the anode material.

[0011] Preferably, in step (1), the pressure holding time of the steam explosion treatment is 60 - 80 s, and the mass ratio of bamboo fibers to water is 1:1 - 1.5.

[0012] Preferably, in step (1), the length of the bamboo fibers is 2 - 5 mm; the diameter of the pretreated bamboo fibers is 2 - 3 μm, and the length is 0.02 - 0.05 mm.

[0013] Preferably, in step (2), the preparation method of the aldehyde-functionalized bamboo fibers is as follows: Mix the pretreated bamboo fibers, sodium periodate, and water with a mass ratio of 1:2 - 4:80 - 100 to obtain a reaction solution, adjust the pH of the reaction solution to 5.5 - 6 with dilute hydrochloric acid, then under light-shielding and stirring conditions, heat it to 50 - 60 °C and stir and react for 6 - 8 h to obtain the aldehyde-functionalized bamboo fibers.

[0014] Preferably, in step (3), the preparation method of lithium amino acid is as follows: Add 3-aminopropanesulfonic acid or 6-aminohexanoic acid and lithium hydroxide with a molar ratio of 1:1 to water, carry out a mixed reaction at 40 - 50 °C for 40 - 50 min, and evaporate to dryness to obtain lithium amino acid.

[0015] Preferably, in step (3), the method of the Schiff base reaction is as follows: Mix the aldehyde-functionalized bamboo fibers, lithium amino acid, glacial acetic acid, and solvent, carry out a mixed reaction at 45 - 55 °C for 3 - 5 h to obtain lithium salt grafted bamboo fibers; the mass ratio of the aldehyde-functionalized bamboo fibers, lithium amino acid, and glacial acetic acid is 1:2 - 4:20 - 30.

[0016] Preferably, in step (4), the mass fraction of the dispersion of lithium salt grafted bamboo fibers is 5 - 8%, the mass ratio of isopropyl titanate to ethanol is 15:180 - 200, and the time of the mixed reaction is 24 - 26 h.

[0017] Preferably, in step (5), the carbonization treatment is to first heat the bamboo fibers with in-situ grown lithium titanate to 300 - 400 °C in an inert atmosphere, hold the temperature for 2 - 3 h, and then continue to heat to 600 - 700 °C and hold the temperature for 5 - 6 h.

[0018] The present invention provides a negative electrode material, which is prepared by the method for preparing a negative electrode material as described above.

[0019] The present invention provides an application of the negative electrode material as described above in the preparation of a shaped battery.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] (1) In the present invention, aldehyde group modification is first carried out on bamboo fibers, and then through Schiff base reaction, lithium carboxylate is introduced by chemical bonding of C=N bonds. Finally, in-situ reaction is carried out using isopropyl titanate and lithium carboxylate chemically bonded to the terminal of bamboo fibers to form lithium titanate active negative electrode material. Since lithium carboxylate is chemically bonded to the surface of bamboo fibers, it can be better and evenly dispersed on the surface of bamboo fibers and closely adhere to bamboo fibers when reacting with isopropyl titanate. After carbonization treatment, the carbon material formed by bamboo fibers and the lithium titanate active negative electrode material can be better and closely compounded, and the carbon material and the lithium titanate active negative electrode material are more evenly dispersed, and the two can better play a synergistic role, reduce the charge transfer resistance, and improve the initial Coulomb efficiency, the first discharge capacity and the cycle stability.

[0022] (2) After chemically bonding 3-aminopropanesulfonic acid to the surface of bamboo fibers, the present invention can simultaneously introduce nitrogen element and sulfur element, and then carry out nitrogen doping and sulfur doping on the carbon material and lithium titanate. The doped nitrogen element and sulfur element can play a synergistic role with the carbon material and lithium titanate, thereby improving the initial Coulomb efficiency, the first discharge capacity and the cycle stability of the negative electrode material, and reducing the charge transfer resistance.

[0023] (3) Experimental results show that when the steam pressure of steam explosion treatment is too high or too low, the decomposition degree of bamboo fibers is too small or too large, which is not conducive to improving the electrochemical performance of the negative electrode material. When the steam pressure is too high, the decomposition degree of bamboo fibers is too large and the structure is damaged, which is not conducive to the grafting of lithium salts, and thus not conducive to the doping and introduction of nitrogen element and lithium element, resulting in poor electrochemical performance of the negative electrode material; when the steam pressure is too low, the decomposition degree of bamboo fibers is too small, resulting in inability to graft more lithium salts more evenly, thus not conducive to improving the electrochemical performance.

[0024] (4) The negative electrode material prepared by the present invention is applied to a lithium ion battery and has a high first discharge capacity at different rates, which is between 545 and 598 mAh / g, and the capacity retention rate after 1000 cycles at different rates is greater than 98.5%, indicating that the negative electrode material prepared by the present invention has high cycle stability. In addition, the test results of the initial Coulomb efficiency and the charge transfer resistance show that the negative electrode material prepared by the present invention has good initial Coulomb efficiency, which is between 95.3 and 96.4%, and the charge transfer resistance is between 97.2 and 129.6 Ω. Detailed implementation manners

[0025] The following embodiments are intended to further illustrate the content of the present invention rather than limit the protection scope of the present invention.

[0026] I. The specific embodiments of the preparation method of the negative electrode material of the present invention are as follows:

[0027] Example 1

[0028] The preparation method of the negative electrode material in this example includes the following steps:

[0029] (1) Mix bamboo fibers with a length of 2 - 5 mm and water in a mass ratio of 1:1, then add them to a steam explosion device. Keep the pressure at 1.8 MPa for 60 s and then release the pressure for steam explosion treatment. After cooling, washing with water, drying, and pulverizing, pre-treated bamboo fibers with a diameter of 2 - 3 μm and a length of 0.02 - 0.05 mm are obtained.

[0030] (2) Add pre-treated bamboo fibers, sodium periodate, and water in a mass ratio of 1:2:80 to a reaction kettle, stir evenly to obtain a reaction solution. Then add dilute hydrochloric acid to the reaction solution to adjust the pH of the reaction solution to 5.5. Then, under the conditions of light avoidance and stirring, heat to 50 °C and stir for 6 h. Cool to room temperature, filter, and wash the filtered solid with water and ethanol in sequence. After drying, aldehyde-functionalized bamboo fibers are obtained.

[0031] (3) Add aldehyde-functionalized bamboo fibers, lithium amino acid, and acetonitrile to a reaction kettle, stir evenly, then add glacial acetic acid, stir evenly and heat to 45 °C, stir and reflux for 3 h. Cool to room temperature, filter, and wash the filtered solid with acetonitrile, water, and ethanol in sequence. After drying, lithium salt-grafted bamboo fibers are obtained; the mass ratio of aldehyde-functionalized bamboo fibers, lithium amino acid, acetonitrile, and glacial acetic acid is 1:2:120:20; the preparation method of lithium amino acid is as follows: Add 6-aminohexanoic acid and lithium hydroxide in a molar ratio of 1:1 to water, heat to 40 °C, stir and react for 40 min, evaporate the water to dryness to obtain lithium amino acid.

[0032] (4) Stir lithium salt-grafted bamboo fibers and ethanol evenly to obtain a 5% lithium salt-grafted bamboo fiber dispersion; stir isopropyl titanate and ethanol in a mass ratio of 15:180 evenly to obtain a mixed solution; under stirring conditions, drop the mixed solution into the lithium salt-grafted bamboo fiber dispersion. After dropping, heat to 130 °C and stir for 24 h. Cool to room temperature, filter, and wash the filtered solid with acetone, water, and ethanol in sequence. After drying, bamboo fibers with in-situ grown lithium titanate are obtained.

[0033] (5) Heat the bamboo fibers with in-situ grown lithium titanate to 300 °C under a nitrogen atmosphere, hold for 2 h, then continue to heat to 600 °C and hold for 5 h to complete the carbonization treatment. After cooling and pulverizing, the negative electrode material is obtained.

[0034] Example 2

[0035] The preparation method of the negative electrode material in this example includes the following steps:

[0036] (1) Mix bamboo fibers with a length of 2 - 5 mm and water in a mass ratio of 1:1.2, add them to a steam explosion device, hold the pressure at 1.8 MPa for 70 s, then release the pressure for steam explosion treatment. After cooling, washing with water, drying, and pulverizing, pre-treated bamboo fibers with a diameter of 2 - 3 μm and a length of 0.02 - 0.05 mm are obtained.

[0037] (2) Add the pre-treated bamboo fibers, sodium periodate, and water with a mass ratio of 1:3:90 to a reaction kettle, stir evenly to obtain a reaction solution. Then add dilute hydrochloric acid to the reaction solution to adjust the pH of the reaction solution to 5.8. Then, under light-shielded and stirring conditions, heat to 55 °C and stir and react for 7 h. Cool to room temperature, filter, and wash the filtered solid successively with water and ethanol, and dry to obtain aldehyde-group grafted bamboo fibers.

[0038] (3) Add the aldehyde-group grafted bamboo fibers, lithium amino acid, and acetonitrile to a reaction kettle, stir evenly, then add glacial acetic acid, stir evenly and heat to 50 °C, stir and reflux for 4 h. Cool to room temperature, filter, and wash the filtered solid successively with acetonitrile, water, and ethanol, and dry to obtain lithium salt grafted bamboo fibers; the mass ratio of the aldehyde-group grafted bamboo fibers, lithium amino acid, acetonitrile, and glacial acetic acid is 1:3:130:25; the preparation method of lithium amino acid is as follows: Add aminocaproic acid and lithium hydroxide with a molar ratio of 1:1 to water, heat to 45 °C, stir and react for 45 min, evaporate the water to dryness to obtain lithium amino acid.

[0039] (4) Stir the lithium salt grafted bamboo fibers and ethanol evenly to obtain a 7% mass fraction lithium salt grafted bamboo fiber dispersion; stir the isopropyl titanate and ethanol with a mass ratio of 15:190 evenly to obtain a mixed solution; under stirring conditions, drop the mixed solution into the lithium salt grafted bamboo fiber dispersion. After the dropping is completed, heat to 140 °C, stir and react for 25 h. Cool to room temperature, filter, and wash the filtered solid successively with acetone, water, and ethanol, and dry to obtain bamboo fibers with in-situ grown lithium titanate.

[0040] (5) Heat the bamboo fibers with in-situ grown lithium titanate to 350 °C under a nitrogen atmosphere, hold for 2.5 h, then continue to heat to 650 °C and hold for 5.5 h to complete the carbonization treatment. After cooling and pulverizing, the negative electrode material is obtained.

[0041] Example 3

[0042] The preparation method of the negative electrode material of this example includes the following steps:

[0043] (1) Mix bamboo fibers with a length of 2 - 5 mm and water in a mass ratio of 1:1.5, then add them to a steam explosion device. Keep the pressure at 1.9 MPa for 80 s and then release the pressure for steam explosion treatment. After cooling, washing with water, drying, and pulverizing, pretreated bamboo fibers with a diameter of 2 - 3 μm and a length of 0.02 - 0.05 mm are obtained.

[0044] (2) Add the pretreated bamboo fibers, sodium periodate, and water with a mass ratio of 1:4:100 to a reaction kettle, stir evenly to obtain a reaction solution. Then add dilute hydrochloric acid to the reaction solution to adjust the pH of the reaction solution to 6. Then, under the conditions of light avoidance and stirring, heat it to 60 °C and stir and react for 8 h. Cool to room temperature, filter, and wash the filtered solid successively with water and ethanol, and then dry to obtain aldehyde - group grafted bamboo fibers.

[0045] (3) Add the aldehyde - group grafted bamboo fibers, lithium amino acid, and acetonitrile to a reaction kettle, stir evenly, then add glacial acetic acid, stir evenly and then heat to 55 °C, stir and reflux for 5 h. Cool to room temperature, filter, and wash the filtered solid successively with acetonitrile, water, and ethanol, and then dry to obtain lithium - salt grafted bamboo fibers; the mass ratio of the aldehyde - group grafted bamboo fibers, lithium amino acid, acetonitrile, and glacial acetic acid is 1:4:150:30; the preparation method of lithium amino acid is as follows: Add 6 - aminohexanoic acid and lithium hydroxide with a molar ratio of 1:1 to water, heat to 50 °C, stir and react for 50 min, evaporate the water to dryness to obtain lithium amino acid.

[0046] (4) Stir the lithium - salt grafted bamboo fibers and ethanol evenly to obtain a lithium - salt grafted bamboo fiber dispersion with a mass fraction of 8%; stir the isopropyl titanate and ethanol with a mass ratio of 15:200 evenly to obtain a mixed solution; under stirring conditions, drop the mixed solution into the lithium - salt grafted bamboo fiber dispersion. After the dropping is completed, heat to 150 °C, stir and react for 26 h. Cool to room temperature, filter, and wash the filtered solid successively with acetone, water, and ethanol, and then dry to obtain bamboo fibers with in - situ grown lithium titanate.

[0047] (5) Heat the bamboo fibers with in - situ grown lithium titanate to 400 °C in a nitrogen atmosphere, keep warm for 3 h, then continue to heat to 700 °C and keep warm for 6 h to complete the carbonization treatment. After cooling and pulverizing, the negative electrode material is obtained.

[0048] Example 4

[0049] The preparation method of the negative electrode material of this example includes the following steps:

[0050] (1) Mix bamboo fibers with a length of 2 - 5 mm and water in a mass ratio of 1:1, then add them to a steam explosion device. Keep the pressure at 1.8 MPa for 60 s and then release the pressure for steam explosion treatment. After cooling, washing with water, drying, and pulverizing, pretreated bamboo fibers with a diameter of 2 - 3 μm and a length of 0.02 - 0.05 mm are obtained.

[0051] (2) Add the pretreated bamboo fibers, sodium periodate, and water in a mass ratio of 1:2:80 to a reaction kettle, stir evenly to obtain a reaction solution. Then add dilute hydrochloric acid to the reaction solution to adjust the pH of the reaction solution to 5.5. Then, under the conditions of light avoidance and stirring, heat to 50 °C and stir for 6 h. Cool to room temperature, filter, and wash the filtered solid successively with water and ethanol, and then dry to obtain aldehyde-group grafted bamboo fibers.

[0052] (3) Add the aldehyde-group grafted bamboo fibers, lithium amino acid, and acetonitrile to a reaction kettle, stir evenly, then add glacial acetic acid, stir evenly and heat to 45 °C, stir and reflux for 3 h. Cool to room temperature, filter, and wash the filtered solid successively with acetonitrile, water, and ethanol, and then dry to obtain lithium salt grafted bamboo fibers; the mass ratio of the aldehyde-group grafted bamboo fibers, lithium amino acid, acetonitrile, and glacial acetic acid is 1:2:120:20; the preparation method of lithium amino acid is as follows: Add 3-aminopropanesulfonic acid and lithium hydroxide in a molar ratio of 1:1 to water, heat to 40 °C, stir and react for 40 min, evaporate the water to dryness to obtain lithium amino acid.

[0053] (4) Stir the lithium salt grafted bamboo fibers and ethanol evenly to obtain a lithium salt grafted bamboo fiber dispersion with a mass fraction of 5%; stir the isopropyl titanate and ethanol with a mass ratio of 15:180 evenly to obtain a mixed solution; under stirring conditions, drop the mixed solution into the lithium salt grafted bamboo fiber dispersion. After the dropping is completed, heat to 130 °C and stir and react for 24 h. Cool to room temperature, filter, and wash the filtered solid successively with acetone, water, and ethanol, and then dry to obtain bamboo fibers with lithium titanate grown in-situ.

[0054] (5) Heat the bamboo fibers with lithium titanate grown in-situ to 300 °C in a nitrogen atmosphere, keep warm for 2 h, then continue to heat to 600 °C and keep warm for 5 h to complete the carbonization treatment. After cooling and pulverizing, a negative electrode material is obtained.

[0055] Comparative Example 1

[0056] The difference between the preparation method of the negative electrode material in this comparative example and the preparation method of the negative electrode material in Example 1 is only that in the preparation method of the negative electrode material in this comparative example, the steam explosion treatment in step (1) is omitted, and the bamboo fibers with a length of 2 - 5 mm are directly pulverized to obtain pretreated bamboo fibers with a diameter of 2 - 3 μm and a length of 0.02 - 0.05 mm.

[0057] Comparative Example 2

[0058] The difference between the preparation method of the negative electrode material in this comparative example and the preparation method of the negative electrode material in Example 1 is only that the steam pressure during the steam explosion treatment in the preparation method of the negative electrode material in this comparative example is 2.5 MPa.

[0059] Comparative Example 3

[0060] The difference between the preparation method of the negative electrode material in this comparative example and the preparation method of the negative electrode material in Example 1 is only that the steam pressure during the steam explosion treatment in the preparation method of the negative electrode material in this comparative example is 1.2 MPa.

[0061] Comparative Example 4

[0062] The difference between the preparation method of the negative electrode material in this comparative example and the preparation method of the negative electrode material in Example 1 is only that step (3) is omitted in the preparation method of the negative electrode material in this comparative example, and the steps of step (4) are as follows: Add aldehyde-functionalized bamboo fibers, lithium amino acid, and ethanol into a reaction kettle, stir evenly to obtain a bamboo fiber dispersion. The mass ratio of aldehyde-functionalized bamboo fibers to lithium amino acid is 1:2, and the mass fraction of aldehyde-functionalized bamboo fibers in the bamboo fiber dispersion is 5%. The lithium amino acid is the same as that in Example 1; Stir evenly the isopropyl titanate and ethanol with a mass ratio of 15:180 to obtain a mixed solution; Drop the mixed solution into the bamboo fiber dispersion. After the dropping is completed, heat to 130 °C, stir and react for 24 h, cool to room temperature, filter, and wash the solid obtained by filtration successively with acetone, water, and ethanol, and dry to obtain bamboo fibers with lithium titanate grown in-situ.

[0063] Comparative Example 5

[0064] The preparation method of the negative electrode material in this comparative example includes the following steps:

[0065] (1) Mix bamboo fibers with a length of 2 - 5 mm and water at a mass ratio of 1:1, add them into a steam explosion device, keep the pressure for 60 s under the condition of a steam pressure of 1.8 MPa, then release the pressure for steam explosion treatment. After cooling, washing with water, drying, and pulverizing, obtain pretreated bamboo fibers with a diameter of 2 - 3 μm and a length of 0.02 - 0.05 mm.

[0066] (2) Stir the pretreated bamboo fibers, lithium acetate and ethanol evenly to obtain a pretreated bamboo fiber dispersion. The sum of the mass fractions of the pretreated bamboo fibers and lithium acetate in the pretreated bamboo fiber dispersion is 5%, and the mass ratio of the pretreated bamboo fibers to lithium acetate is 1:2. Stir the isopropyl titanate and ethanol with a mass ratio of 15:180 evenly to obtain a mixed solution. Drop the mixed solution into the pretreated bamboo fiber dispersion. After the dropping is completed, heat it to 130 °C, stir and react for 24 h, cool it to room temperature, filter, and wash the filtered solid successively with acetone, water and ethanol, and dry it to obtain bamboo fibers with lithium titanate grown in-situ.

[0067] (3) Heat the bamboo fibers with lithium titanate grown in-situ to 300 °C in a nitrogen atmosphere, keep it warm for 2 h, then continue to heat it to 600 °C and keep it warm for 5 h to complete the carbonization treatment. After cooling and pulverizing, the negative electrode material is obtained.

[0068] Comparative Example 6

[0069] The difference between the preparation method of the negative electrode material in this comparative example and the preparation method of the negative electrode material in Example 1 is only that in step (4) of the preparation method of the negative electrode material in this comparative example, "drop the mixed solution into the lithium salt grafted bamboo fiber dispersion under stirring conditions" is adjusted to "drop the lithium salt grafted bamboo fiber dispersion into the mixed solution under stirring conditions".

[0070] II. Specific examples of the negative electrode material of the present invention are as follows:

[0071] The negative electrode material of this example is prepared by the preparation method of any negative electrode material in Examples 1-4.

[0072] III. Specific examples of the application of the negative electrode material of the present invention in the preparation of special-shaped batteries are as follows:

[0073] The application of the negative electrode material of this example in the preparation of special-shaped batteries includes the following steps: Use the negative electrode material prepared by the preparation method of any negative electrode material in Examples 1-4 as the negative electrode material for lithium-ion batteries and apply it to lithium-ion batteries.

[0074] Effect Example

[0075] To evaluate the performance of the anode materials prepared in each example and comparative example when used in lithium-ion batteries, the anode material, polyvinylidene fluoride binder, and acetylene black conductive agent with a mass ratio of 8:1:1 were added to an agate mortar and ground evenly to obtain a mixture. Then, the mixture and N-methylpyrrolidone were stirred evenly to obtain a slurry. The slurry was coated on a copper foil and dried in a vacuum drying oven at 100 °C for 12 h. After cooling to room temperature, an anode sheet was obtained. Then, a polyethylene separator, a cathode sheet, an anode sheet, a gasket, a spring piece, an electrolyte, a negative electrode case, and a positive electrode case were assembled into a button battery. Next, the battery was subjected to constant current charge-discharge testing using a workstation. The voltage range during testing was 0.01 - 3.0 V. The charge-discharge capacities were tested under the conditions of 1C, 5C, and 10C, and the capacity retention rate after 1000 cycles was calculated. The initial Coulombic efficiency was calculated based on the charge-discharge capacity of the first cycle at a 0.2C rate. The initial Coulombic efficiency is equal to the ratio of the discharge capacity and charge capacity of the first cycle. Finally, electrochemical impedance testing was performed using an electrochemical workstation. The test frequency was 0.01 Hz - 25 kHz, and the scanning speed was 0.1 mV / s. The charge transfer resistance of the anode material was determined based on the electrochemical impedance spectrum.

[0076] Table 1 First discharge capacity, capacity retention rate, initial Coulombic efficiency, and charge transfer resistance of different anode materials at different rates

[0077]

[0078]

[0079] As can be seen from Table 1, the anode material prepared by the present invention is applied to a lithium-ion battery and has a high initial discharge capacity at different rates, which is between 545 and 598 mAh / g. Moreover, the capacity retention rate after 1000 cycles at different rates is greater than 98.5%, indicating that the anode material prepared by the present invention has high cycle stability. In addition, the test results of the initial Coulomb efficiency and charge transfer resistance show that the anode material prepared by the present invention has a good initial Coulomb efficiency, which is between 95.3 and 96.4%, and the charge transfer resistance is between 97.2 and 129.6 Ω. The above results show that the present invention first performs aldehyde group modification on bamboo fibers, then through the Schiff base reaction, introduces lithium carboxylate by chemical bonding of C=N bonds, and finally uses isopropyl titanate and lithium carboxylate chemically bonded to the terminal of bamboo fibers to carry out an in-situ reaction to form a lithium titanate active anode material. Since lithium carboxylate is chemically bonded to the surface of bamboo fibers, it can be better uniformly dispersed on the surface of bamboo fibers and closely adhere to bamboo fibers when reacting with isopropyl titanate. After carbonization treatment, the carbon material formed by bamboo fibers and the lithium titanate active anode material can be better tightly compounded, and the carbon material and the lithium titanate active anode material are more uniformly dispersed, and the two can better play a synergistic role, reduce the charge transfer resistance, and improve the initial Coulomb efficiency, initial discharge capacity and cycle stability.

[0080] As can be seen from Examples 1-3 and Example 4, the anode material prepared using 3-aminopropanesulfonic acid has higher initial Coulomb efficiency, initial discharge capacity and cycle stability, and smaller charge transfer resistance than the anode material prepared using aminohexanoic acid. This may be because after 3-aminopropanesulfonic acid is chemically bonded to the surface of bamboo fibers, nitrogen and sulfur elements can be introduced simultaneously, and then nitrogen doping and sulfur doping are carried out on the carbon material and lithium titanate. The doped nitrogen and sulfur elements can play a synergistic role with the carbon material and lithium titanate, thereby improving the initial Coulomb efficiency, initial discharge capacity and cycle stability of the anode material and reducing the charge transfer resistance.

[0081] As can be seen from Example 1 and Comparative Example 1, steam explosion treatment of bamboo fibers can perform plastic modification on bamboo fibers, shorten the fiber length of bamboo fibers, cause partial fibrillation, and reduce the degree of polymerization, so that bamboo fibers can be better aldehyde group modified, introduce more aldehyde groups, and then graft more lithium salts, thereby doping more nitrogen and lithium elements and improving the electrochemical performance of the anode material.

[0082] As can be seen from Example 1 and Comparative Examples 2-3, when the steam pressure for steam explosion treatment is too high or too low, the degree of bamboo fiber decomposition is too small or too large, which is not conducive to improving the electrochemical performance of the anode material. When the steam pressure is too high, the degree of bamboo fiber decomposition is too large and the structure is damaged, which is not conducive to the grafting of lithium salts, and thus not conducive to the doping and introduction of nitrogen and lithium elements, resulting in poor electrochemical performance of the anode material; when the steam pressure is too low, the degree of bamboo fiber decomposition is too small, resulting in the inability to graft more lithium salts more uniformly, thus not conducive to improving the electrochemical performance.

[0083] As can be seen from Example 1 and Comparative Examples 4-5, when the lithium salt is replaced by physical mixing in the form of chemical grafting, the electrochemical performance of the anode material becomes worse, and the electrochemical performance of the anode material prepared in Comparative Example 5 is the worst. From the above results, it can be seen that when using lithium amino acid, due to the doping of nitrogen element, the electrochemical performance of the anode material can be further improved.

[0084] As can be seen from Example 1 and Comparative Example 6, when the lithium salt grafted bamboo fiber dispersion is added dropwise to the mixed solution, the electrochemical performance of the prepared anode material becomes worse. This may be because the dispersion of the lithium salt grafted bamboo fiber is poor. When it is added dropwise to the mixed solution, the lithium salt grafted bamboo fiber cannot participate in the reaction in time and quickly, resulting in the uneven and incomplete reaction of the lithium element grafted on the bamboo fiber and the titanium element in the mixed solution, affecting the electrochemical performance of the anode material. When the mixed solution is added to the lithium salt grafted bamboo fiber dispersion, since the lithium salt grafted bamboo fiber dispersion is in a state of rapid agitation, the titanium element in the mixed solution can participate in the reaction more quickly and fully, and then form uniformly loaded lithium titanate, improving the electrochemical performance of the anode material.

Claims

1. A method for preparing a negative electrode material, characterized in that: The following steps are involved: (1) Mixing bamboo fiber and water and subjecting them to steam explosion treatment to obtain pretreated bamboo fiber; the steam pressure during the steam explosion treatment is 1.8-1.9 MPa; (2) reacting the pretreated bamboo fiber with periodate in an acidic environment to obtain aldehyde-modified bamboo fiber; (3) The aldehyde group in the aldehyde-modified bamboo fiber and the amino group in the amino acid lithium are subjected to a Schiff base reaction to obtain lithium salt-grafted bamboo fiber; the amino acid lithium is prepared by reacting 3-aminopropanesulfonic acid or aminocaproic acid with lithium hydroxide; (4) adding the mixed solution dropwise to the lithium salt grafted bamboo fiber dispersion and heating it to 130-150° C. to react with the mixture to obtain bamboo fibers with in-situ growth of lithium titanate; the mixed solution is prepared by mixing isopropyl titanate and ethanol; (5) The bamboo fiber with in-situ grown lithium titanate is carbonized to obtain the negative electrode material.

2. The method for preparing the negative electrode material according to claim 1, characterized in that: The holding time of the steam explosion treatment in step (1) is 60-80 seconds, and the mass ratio of bamboo fiber to water is 1:1-1.

5.

3. The method for preparing the negative electrode material according to claim 1, characterized in that: In step (1), the length of the bamboo fiber is 2-5 mm; the diameter of the pretreated bamboo fiber is 2-3 μm, and the length is 0.02-0.05 mm.

4. The method for preparing the negative electrode material according to claim 1, characterized in that: The preparation method of the aldehyded bamboo fiber in step (2) is as follows: pretreated bamboo fiber, sodium periodate and water in a mass ratio of 1:2-4:80-100 are mixed to obtain a reaction solution, the pH of the reaction solution is adjusted to 5.5-6 with dilute hydrochloric acid, and then heated to 50-60° C. under light-proof and stirring conditions, and stirred for reaction for 6-8 hours to obtain the aldehyded bamboo fiber.

5. The method for preparing the negative electrode material according to claim 1, characterized in that: In step (3), the preparation method of amino acid lithium is as follows: 3-aminopropanesulfonic acid or aminocaproic acid and lithium hydroxide in a molar ratio of 1:1 are added to water, mixed and reacted at 40-50° C. for 40-50 minutes, and the water is evaporated to obtain amino acid lithium.

6. The method for preparing the negative electrode material according to claim 1, characterized in that: In step (3), the Schiff base reaction method is as follows: aldehyde-modified bamboo fiber, amino acid lithium, glacial acetic acid and solvent are mixed, and mixed and reacted at 45-55° C. for 3-5 hours to obtain lithium salt grafted bamboo fiber; the mass ratio of aldehyde-modified bamboo fiber, amino acid lithium and glacial acetic acid is 1:2-4:20-30.

7. The method for preparing the negative electrode material according to claim 1, characterized in that: In step (4), the mass fraction of the lithium salt grafted bamboo fiber dispersion is 5-8%, the mass ratio of isopropyl titanate to ethanol is 15:180-200, and the mixing reaction time is 24-26 hours.

8. The method for preparing the negative electrode material according to claim 1, characterized in that: In step (5), the carbonization treatment is to heat the bamboo fiber with in-situ grown lithium titanate to 300-400°C in an inert atmosphere, keep it warm for 2-3 hours, and then continue to heat it to 600-700°C and keep it warm for 5-6 hours.

9. A negative electrode material prepared by the method for preparing a negative electrode material according to any one of claims 1 to 8.

10. Use of the negative electrode material according to claim 9 in preparing special-shaped batteries.

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