CN103956475A - Method for preparing lithium titanate of lithium ion battery cathode material - Google Patents

Abstract

The invention relates to a method for preparing lithium titanate, a negative electrode material of a lithium ion battery. Titanium source, dispersant, and deionized water are mixed to form a titanium-containing solution, hydrolyzed under stirring, and the product is collected by centrifugation; the lithium-containing solution is added to the collected product And mix evenly, then carry out hydrothermal reaction, the precipitate obtained is the lithium titanate precursor of nanostructure, wherein Li and Ti molar ratio is 4:5～5:1; Calcining at a low temperature in an atmosphere of a reducing gas to obtain lithium titanate, a negative electrode material for a nitrogen-doped nanoscale lithium ion battery. Compared with the prior art, the present invention has low equipment requirements and is easy to industrialized production, and the lithium titanate material prepared by the present invention has both the advantages of nanostructure and doping modification, and at the same time improves the ionic conductivity of the material And electronic conductivity, so that the material has excellent specific capacity performance and cycle performance.

Description

A method for preparing lithium titanate, a negative electrode material for lithium ion batteries

technical field

The invention belongs to the technical field of chemical power sources, and in particular relates to a method for preparing lithium titanate, a negative electrode material of a lithium ion battery.

Background technique

At present, the anode materials of commercial lithium-ion batteries are mainly carbon-based materials. Although the cost of carbon anode materials is low, they still have disadvantages such as poor safety performance, low initial charge and discharge efficiency, and thermal runaway at high temperatures. Lithium titanate (Li ₄ Ti ₅ O ₁₂ ) with a spinel structure has the advantages of "zero strain effect" in which the volume does not change during the intercalation and extraction of lithium ions, and a chemical diffusion coefficient that is an order of magnitude larger than that of carbon anode materials. It is considered to be one of the most promising anode materials. However, low electronic conductivity is currently the main obstacle restricting the application of Li ₄ Ti ₅ O ₁₂ in power batteries. It is particularly important to improve the conductivity of Li ₄ Ti ₅ O ₁₂ and improve the high-current charge and discharge performance of Li ₄ Ti ₅ O ₁₂ .

The current main ways of Li ₄ Ti ₅ O ₁₂ modification are: (1) Ion doping: through the doping of other elements, the valence structure of the material surface is changed, electron holes are formed, and the conductivity of the material is improved to improve its electrical conductivity. chemical properties. Journal of the American Chemical Society (Journal of the American Chemical Society) 130 (2008) 14930-14931 uses a simple high-temperature solid-phase synthesis to prepare a nitrogen-doped lithium titanate material in an ammonia atmosphere. CN201310359192.0 discloses a preparation method of a titanium nitride-coated lithium titanate material, which adopts a high-temperature solid-phase method and sinters at a high temperature in a nitrogen-containing reducing atmosphere to obtain the material. High-temperature solid-phase doping makes the material particles agglomerate, which makes the contact between the material and the electrolyte insufficient, ion transmission is difficult, and the high-current discharge effect is poor. (2) Nanometerization: It can shorten the diffusion path of Li ⁺ , reduce the diffusion resistance of Li ⁺ , slow down the polarization of the electrode, and increase the contact area between the electrode active material and the electrolyte, so that the Li ⁺ de/intercalation reaction can proceed smoothly. more fully. Hydrothermal synthesis is a simple method for synthesizing nanomaterials, which has been widely used in the field of nanomaterials. Journal of Materials Chemistry (Journal of Materials Chemistry) 19 (2009) 5980-5984 uses TiO ₂ colloid and LiOH as reaction raw materials, in ethanol/water mixed solution, hydrothermally prepares lithium titanate microspheres with mesoporous structure, and has excellent material properties , but the process is complex and requires high equipment.

The Chinese patent with the application number 201310432347.9 discloses a preparation method of lithium titanate. Titanium source, lithium source, inorganic additives, organic additives and water are made into a slurry; then atomized and dried into powder in an atomizing dryer; Finally, under the nitrogen-hydrogen mixed gas atmosphere, the atomized and dried powder is roasted at a temperature above 700 degrees for 5-10 hours and cooled to obtain lithium titanate. The method is easy for large-scale production, and the reducing atmosphere is easy to generate a small amount of Ti ³⁺ , which improves the conductivity of the material. However, when the process is sintered above 700 degrees, even if there are nanoparticles, the material particles tend to become larger during high-temperature sintering, and it is difficult to achieve the high rate performance of nanomaterials.

Contents of the invention

The purpose of the present invention is to provide a method for preparing lithium titanate, a negative electrode material for lithium ion batteries, in order to overcome the defects in the above-mentioned prior art. Diffusion path, thereby improving its performance during high-rate discharge to meet the current demand for lithium-ion batteries.

The purpose of the present invention can be achieved through the following technical solutions:

A method for preparing lithium titanate, an anode material for lithium ion batteries, comprising the following steps:

(1) Mix the titanium source, dispersant, and deionized water to form a titanium-containing solution, hydrolyze it under stirring, and collect the product by centrifugation;

(2) Add lithium-containing solution to the product collected in step (1) and mix uniformly, then carry out hydrothermal reaction, and the precipitate obtained is a nanostructured lithium titanate precursor, wherein the molar ratio of Li to Ti is 4:5 ~5:1;

(3) Calcining the lithium titanate precursor obtained in step (2) at a low temperature in an atmosphere of a nitrogen-containing reducing gas to obtain lithium titanate, a negative electrode material for a nitrogen-doped nanoscale lithium ion battery.

The titanium source in step (1) is selected from one or more of tetrabutyl titanate, tetraethyl titanate, titanium isopropoxide, titanium tetrachloride or titanyl sulfate.

The dispersant described in step (1) is selected from ethanol, ethylene glycol or cyclohexane.

The ratio of the titanium source to the dispersant is 0.002mol:1L-5mol:1L, and the volume ratio of the dispersant to deionized water is 10:1-1000:1. If the ratio of titanium source to dispersant is too low, the production cost will be increased, and if it is too high, the titanium source will be hydrolyzed too quickly, and the particle size of the produced material will increase.

As a preferred embodiment, the ratio of the titanium source to the dispersant is 0.005 mol:1L˜0.05 mol:1L, and the ratio of absolute ethanol to deionized water is 400:1˜600:1.

The lithium-containing solution described in step (2) is prepared by dissolving a lithium-containing compound in deionized water, and the lithium-containing compound is lithium hydroxide, lithium acetate, lithium nitrate, lithium carbonate or lithium chloride.

The concentration of lithium in the lithium-containing solution is 0.1-1 mol/L.

The temperature during the hydrothermal reaction in step (2) is 80-180° C., and the time for the hydrothermal reaction is 10-72 hours. If the temperature is too low, the water heating time will increase, which is not conducive to industrial production; if the temperature is too high, the requirements for production equipment will be higher.

As a preferred embodiment, the hydrothermal temperature is 130-150° C., and the hydrothermal time is 14-24 hours.

The nitrogen-containing reducing gas described in step (3) is ammonia or the mixed gas of ammonia, nitrogen, argon and hydrogen, the heating rate of calcination is 2-10°C/min, the temperature of calcination is 350-600°C, and the calcination The time is 2 to 10 hours. If the heating rate is too fast, the calcination temperature is too high, and the calcination time is too long, it will cause the material to agglomerate and it is difficult to maintain the nanostructure, while the heating rate is too slow, the calcination temperature is too low, and the calcination time is too short, which will lead to poor crystallinity of the material and affect performance.

As a preferred embodiment, the heating rate is 3°C/min, the calcination temperature is 500-550°C, and the calcination time is 5-7 hours.

The negative electrode material lithium titanate of the lithium ion battery prepared in step (3) has a spinel structure.

Mix lithium titanate, the lithium ion battery negative electrode material synthesized by the method of the present invention, with conductive carbon black and binder polyvinylidene fluoride (PVDF) in a mass ratio of 80:10:10, coat the copper foil, and dry Afterwards, it was cut into negative pole pieces and dried under vacuum at 100°C for 24 hours. With metal lithium as the counter electrode, the electrolyte LiPF ₆ salt is dissolved in a mixed solution of ethylene carbonate (EC)/dimethyl carbonate (DMC)/ethyl methyl carbonate (EMC) with a mass ratio of 1:1:1 to form Electrolyte, the concentration of the electrolyte is 1mol/L, assembled into a button cell in an argon glove box. The electrochemical performance test was carried out with Wuhan Landian CT2001A battery tester, and the charging and discharging voltage range was 1.0V-2.5V (vs. Li ⁺ /Li).

Compared with the prior art, the present invention prepares the nanostructured lithium titanate precursor through the traditional hydrothermal method, and then calcines it at a low temperature in an atmosphere of nitrogen-containing reducing gas, and the lower calcining temperature will not cause nano-precursor particles The overgrowth of nanostructures is maintained, while nitrogen doping is achieved in an atmosphere of nitrogen-containing reducing gas. The nanostructure can increase the contact area between the material and the electrolyte, shorten the diffusion path of lithium ions inside the material, and facilitate the conduction of ions inside the material; nitrogen doping can change the valence structure of the material surface, form electron holes, and improve the Conductivity, thereby improving the high-rate discharge performance of the material. The prepared material of the present invention combines the advantages of nanostructure and nitrogen doping modification, improves the high-rate discharge performance of the material, and can meet the current requirements for fast charging and discharging of power batteries.

Description of drawings

Fig. 1 is the SEM figure of lithium ion battery negative electrode material lithium titanate that embodiment 1 makes;

Fig. 2 is the capacity retention performance curve graph of the negative electrode material lithium titanate of lithium ion battery that embodiment 1 and comparative example 1 make under different rate;

FIG. 3 is a graph showing cycle performance curves of lithium titanate, a lithium ion battery negative electrode material prepared in Example 1, at different rates.

Detailed ways

The method for preparing lithium-ion battery negative electrode material lithium titanate can adopt the following steps:

(1) Mix the titanium source, dispersant, and deionized water to form a titanium-containing solution, hydrolyze it under stirring, and collect the product by centrifugation;

(2) Add the product obtained by centrifugation into the lithium-containing solution and mix evenly, and perform a hydrothermal reaction. The temperature of the hydrothermal reaction is 80-180° C., and the reaction time is 10-72 hours. The precipitate generated after the reaction is a nanostructure Lithium titanate precursor; wherein the molar ratio of Li to Ti is 4:5 to 5:1;

(3) The nanostructured lithium titanate precursor obtained in step (2) is heated to 350-600°C at a rate of 2-10°C/min in an atmosphere of a nitrogen-containing reducing gas, calcined for 2-10 hours, and then naturally Cool to room temperature to obtain nanoscale nitrogen-doped lithium ion battery negative electrode material lithium titanate.

In step (1), the titanium source is selected from one or more of tetrabutyl titanate, tetraethyl titanate, titanium isopropoxide, titanium tetrachloride or titanyl sulfate, and the dispersant is selected from ethanol, ethylene disulfide Alcohol or cyclohexane, the ratio of titanium source and dispersant in step (1) is 0.002mol:1L-5mol:1L, and the volume ratio of dispersant to deionized water is 10:1-1000:1.

The lithium-containing solution in step (2) is prepared by dissolving a lithium-containing compound in deionized water, and the lithium-containing compound is lithium hydroxide, lithium acetate, lithium nitrate, lithium carbonate or lithium chloride. The concentration of lithium in the lithium-containing solution is 0.1-1 mol/L.

The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

Example 1

Choose lithium hydroxide as the lithium source, tetrabutyl titanate as the titanium source, and ethanol as the dispersant. According to the molar ratio of Li and Ti as 1:1, mix 0.004mol tetrabutyl titanate, 20mL ethanol, and 2mL water evenly Form a titanium-containing solution, hydrolyze under stirring, and collect the hydrolyzate by centrifugation; add the hydrolyzate to the lithium-containing solution and mix evenly, wherein the lithium-containing solution is obtained by dissolving 0.004mol lithium hydroxide in 20mL water; react at 150°C for 14 hours to form nanostructures Lithium titanate precursor: the obtained lithium titanate precursor was heated up to 550°C at a rate of 3°C/min in an ammonia atmosphere and kept at a constant temperature for 6 hours, and then naturally cooled to room temperature to obtain the lithium titanate material of the present invention.

The SEM image of lithium titanate, the negative electrode material of nano-scale lithium-nitrogen doped ion battery prepared in this embodiment, is shown in Figure 1. From the figure, it can be seen that the material is a nano-sheet structure with an area of about 200nm, and its distribution is relatively large. uniform.

Example 2

Choose lithium acetate as the lithium source, tetraethyl titanate as the titanium source, and cyclohexane as the dispersant. According to the molar ratio of Li and Ti of 0.8:1, mix 0.004mol tetraethyl titanate, 20mL acetone, and 2mL water Uniformly form a titanium-containing solution, hydrolyze under stirring, and collect the hydrolyzate by centrifugation; add the hydrolyzate to the lithium-containing solution and mix evenly, wherein the lithium-containing solution is obtained by dissolving 0.0032mol lithium acetate in 20mL water; react at 80°C for 72h to form nanostructures Lithium titanate precursor; the obtained lithium titanate precursor is heated to 600°C at a rate of 5°C/min in a mixed atmosphere of ammonia and nitrogen and kept at a constant temperature for 2 hours, and then naturally cooled to room temperature to obtain lithium titanate of the present invention Material.

Example 3

Lithium nitrate was selected as the lithium source, titanium isopropoxide was used as the titanium source, and ethylene glycol was used as the dispersant. According to the molar ratio of Li and Ti being 5:1, 0.004mol titanium isopropoxide, 20mL ethylene glycol, and 2mL water were mixed Uniformly form a titanium-containing solution, hydrolyze under stirring, and collect the hydrolyzate by centrifugation; add the hydrolyzate to the lithium-containing solution and mix evenly, wherein the lithium-containing solution is obtained by dissolving 0.02mol lithium nitrate in 20mL water; react at 180°C for 12 hours to form nanostructured titanium Lithium titanate precursor; the obtained lithium titanate precursor was heated to 500°C at a rate of 5°C/min in an atmosphere of ammonia and argon and kept at a constant temperature for 8 hours, and then naturally cooled to room temperature to obtain the lithium titanate material of the present invention.

Example 4

Lithium carbonate is selected as the lithium source, titanium tetrachloride is used as the titanium source, and ethanol is used as the dispersant. According to the molar ratio of Li and Ti being 2:1, 0.004mol titanium tetrachloride, 20mL ethanol, and 2mL water are mixed evenly to form a titanium-containing The solution was hydrolyzed at room temperature under stirring, and the hydrolyzate was collected by centrifugation; the hydrolyzate was added to the lithium-containing solution and mixed evenly, and the lithium-containing solution was obtained by dissolving 0.004mol lithium carbonate in 20mL water; reacted at 200°C for 10h to generate a nanostructured lithium titanate precursor The obtained lithium titanate precursor was heated up to 400°C at a rate of 2°C/min in an ammonia atmosphere and kept at a constant temperature for 10 hours, and then naturally cooled to room temperature to obtain the lithium titanate material of the present invention.

Example 5

Lithium hydroxide was selected as the lithium source, tetrabutyl titanate was used as the titanium source, and ethylene glycol was used as the dispersant. According to the molar ratio of Li and Ti being 4:1, 0.004mol of tetrabutyl titanate, 20 mL of ethylene glycol, Mix 2mL of water evenly to form a titanium-containing solution, hydrolyze at room temperature under stirring, and collect the hydrolyzate by centrifugation; add the hydrolyzate to the lithium-containing solution and mix evenly, and the lithium-containing solution is obtained by dissolving 0.016mol lithium hydroxide in 20mL of water; react at 180°C 12h to generate a nanostructured lithium titanate precursor; the obtained lithium titanate precursor was heated to 600°C at a rate of 8°C/min in a mixed atmosphere of ammonia, nitrogen, and argon and kept at a constant temperature for 4 hours, and then naturally cooled to room temperature. The lithium titanate material of the present invention is obtained.

Example 6

Lithium chloride was selected as the lithium source, titanyl sulfate was used as the titanium source, and ethanol was used as the dispersant. According to the molar ratio of Li and Ti being 3:1, 0.004mol titanyl sulfate, 20mL ethanol, and 2mL water were mixed uniformly to form a titanium-containing solution. , hydrolyzed at room temperature under stirring, and the hydrolyzate was collected by centrifugation; the hydrolyzate was added to the lithium-containing solution and mixed evenly, and the lithium-containing solution was obtained by dissolving 0.016mol lithium chloride in 20mL water; reacted at 150°C for 48h to generate a nanostructured lithium titanate precursor The obtained lithium titanate precursor was heated to 600°C at a rate of 6°C/min in an ammonia atmosphere and kept at a constant temperature for 4 hours, and then naturally cooled to room temperature to obtain the lithium titanate material of the present invention.

Comparative example 1

Choose lithium hydroxide as the lithium source, tetrabutyl titanate as the titanium source, and ethanol as the dispersant. According to the molar ratio of Li and Ti as 1:1, mix 0.004mol tetrabutyl titanate, 20mL ethanol, and 2mL water evenly Form a titanium-containing solution, hydrolyze under stirring, and collect the hydrolyzate by centrifugation; add the hydrolyzate to the lithium-containing solution and mix evenly, wherein the lithium-containing solution is obtained by dissolving 0.004mol lithium hydroxide in 20mL water; react at 150°C for 14 hours to form nanostructures Lithium titanate precursor: the obtained lithium titanate precursor was heated up to 550°C at a rate of 3°C/min in an air atmosphere and kept at a constant temperature for 6 hours, and then naturally cooled to room temperature to obtain an undoped lithium titanate material.

Electrochemical performance test: Lithium titanate, conductive carbon black and binder polyvinylidene fluoride (PVDF), which were prepared in Example 1 and Comparative Example 1, were respectively mixed in a mass ratio of 80:10:10 Mix well, apply on copper foil, cut into negative pole pieces after drying, and vacuum dry at 100°C for 24 hours. With metal lithium as the counter electrode, the electrolyte LiPF ₆ salt is dissolved in a mixed solution of ethylene carbonate (EC)/dimethyl carbonate (DMC)/ethyl methyl carbonate (EMC) with a mass ratio of 1:1:1 to form Electrolyte, the concentration of the electrolyte is 1mol/L, assembled into a button cell in an argon glove box. The electrochemical performance test was carried out with Wuhan Landian CT2001A battery tester. The test results are shown in Figure 2 and Figure 3. The charging and discharging voltage range is 1.0V-2.5V (vs. Li ⁺ /Li). FIG. 2 is a graph showing the capacity retention performance curves of lithium titanate, a lithium ion battery negative electrode material prepared in Example 1 and Comparative Example 1, at different rates. It can be seen from FIG. 2 that the negative electrode material lithium titanate of the lithium ion battery of the present invention has an initial discharge specific capacity of 173.3mAh/g under the condition of a rate of 1C, which is close to the theoretical specific capacity. After the rate is increased to 2C, 5C, and 10C, the capacity is maintained at 165.1, 162.3, and 151.8mAh/g, respectively, after 20 cycles. However, lithium titanate, the anode material for lithium ion batteries prepared in Comparative Example 1, maintained capacities of 170.6, 163, 156.9, and 139.1 mAh/g at 1C, 2C, 5C, and 10C, respectively. Fig. 3 is a diagram of the cycle performance of lithium titanate, the negative electrode material of the lithium ion battery of the present invention, at the rate of 1C and 10C respectively, and the capacity retention rates are 95.8% and 90.3% respectively. The appeal results show that the material has excellent electrochemical performance.

In summary, the present invention relates to a method for preparing lithium titanate, a lithium ion negative electrode material, which realizes N doping and at the same time prepares a nanosheet structure. It can shorten the ion transmission path and improve the conductivity of the material at the same time, and increase the ion diffusion rate of the material. The prepared material has excellent specific capacity performance and cycle performance, and is relatively suitable for industrial production.

The above content is only a basic description of the concept of the present invention, and any equivalent transformation made according to the technical solution of the present invention shall fall within the scope of protection of the present invention.

Claims (9)

1. a method for preparing lithium ion battery negative electrode material lithium titanate, is characterized in that, the method may further comprise the steps: (1) Mix the titanium source, dispersant, and deionized water to form a titanium-containing solution, hydrolyze it under stirring, and collect the product by centrifugation; (2) Add lithium-containing solution to the product collected in step (1) and mix uniformly, then carry out hydrothermal reaction, and the precipitate obtained is a nanostructured lithium titanate precursor, wherein the molar ratio of Li to Ti is 4:5 ~5:1; (3) Calcining the lithium titanate precursor obtained in step (2) at a low temperature in an atmosphere of a nitrogen-containing reducing gas to obtain lithium titanate, a negative electrode material for a nitrogen-doped nanoscale lithium ion battery. 2. a kind of method preparing lithium ion battery negative electrode material lithium titanate according to claim 1 is characterized in that, the titanium source described in step (1) is selected from tetrabutyl titanate, tetraethyl titanate , titanium isopropoxide, titanium tetrachloride or one or more of titanium oxysulfate. 3. a kind of method for preparing lithium ion battery negative electrode material lithium titanate according to claim 1, is characterized in that, the dispersant described in step (1) is selected from ethanol, ethylene glycol or cyclohexane. 4. according to a kind of method for preparing lithium titanate of lithium ion battery negative electrode material described in any one in claim 1-3, it is characterized in that, the ratio relation of titanium source and dispersant is 0.002mol: 1L～5mol: 1L , the volume ratio of dispersant to deionized water is 10:1-1000:1. Preferably, the ratio of the titanium source to the dispersant is 0.005 mol:1L-0.05 mol:1 L, and the ratio of absolute ethanol to deionized water is 400:1-600:1. 5. a kind of method for preparing lithium ion battery negative electrode material lithium titanate according to claim 1, is characterized in that, the lithium-containing solution described in step (2) is made by dissolving lithium-containing compound in deionized water, The lithium-containing compound is lithium hydroxide, lithium acetate, lithium nitrate, lithium carbonate or lithium chloride. 6 . A method for preparing lithium titanate, a negative electrode material for lithium ion batteries, according to claim 5 , wherein the concentration of lithium in the lithium-containing solution is 0.1˜1 mol/L. 7. A method for preparing lithium titanate, a negative electrode material for lithium-ion batteries, according to claim 1, wherein the temperature during the hydrothermal reaction described in step (2) is 80 to 180° C., and the hydrothermal reaction The best time is 10 to 72 hours. Preferably, the hydrothermal temperature is 130-150° C., and the hydrothermal time is 14-24 hours. 8. A kind of method for preparing lithium ion battery negative electrode material lithium titanate according to claim 1, is characterized in that, the nitrogen-containing reducing gas described in step (3) is ammonia or ammonia and nitrogen, argon , a mixed gas of hydrogen, the calcining heating rate is 2-10°C/min, the calcining temperature is 350-600°C, and the calcining time is 2-10 hours. Preferably, the heating rate is 3°C/min, the calcination temperature is 500-550°C, and the calcination time is 5-7 hours. 9. A kind of method for preparing lithium titanate of lithium ion battery negative electrode material according to claim 1, is characterized in that, the lithium ion battery negative electrode material lithium titanate that step (3) makes is spinel type structure.