CN103078087B - A kind of preparation method of lithium titanate/carbon nano tube composite cathode material - Google Patents

Abstract

The invention discloses a preparation method of a lithium titanate/carbon nanotube composite negative electrode material, belonging to the technical field of battery materials. The present invention adopts the chemical vapor deposition method to grow carbon nanotubes on the surface of lithium titanate. Compared with directly doping carbon nanotubes in lithium titanate, it has the characteristics of uniform dispersion and strong binding force. At the same time, the grown carbon nanotubes are easier to The network structure formed on the surface of lithium titanate plays an important role in improving the structural stability of the battery under high-rate discharge conditions. In the present invention, the lithium-ion battery utilizes the high conductivity of carbon nanotubes and the network structure formed to increase the contact probability with lithium titanate, reduce internal resistance, and reduce polarization. At the same time, the larger specific surface area of carbon nanotubes is also It can improve the liquid absorption and retention capacity of the negative electrode material, thereby improving the high-rate discharge capacity of the battery and the cycle capacity of the battery.

Description

A preparation method of lithium titanate/carbon nanotube composite negative electrode material

technical field

The invention relates to a preparation method of a lithium ion battery negative electrode material, in particular to a preparation method of a lithium titanate/carbon nanotube composite negative electrode material, which belongs to the technical field of battery materials.

Background technique

Lithium-ion battery is a new type of energy storage battery developed in recent years. It has attracted people's attention for its advantages of long cycle life, stable working voltage platform, low price and no pollution. It has been widely used in electric vehicles, wind energy storage, etc. Energy, mobile power stations and other fields.

At present, graphite-based materials are mostly used for the negative electrodes of lithium-ion batteries, but the defects of graphite-based negative electrode materials, such as poor cycle life and low safety, limit their wide application in the battery field. Spinel-type lithium titanate is a zero-strain material, which has the advantages of good cycle performance, no reaction with electrolyte, stable charge and discharge voltage platform, high safety, low price and easy preparation. It is a long-life, high-safety material. ideal anode material for batteries. However, the spinite-type lithium titanate material itself has low electronic conductance and ion conductance, and the capacity decays rapidly during high-current charge and discharge, and the rate performance is poor, which affects its application under high-current charge-discharge conditions, so the rate performance is improved. Become the key to the practical process of lithium titanate.

At present, there are two main ways to improve the rate performance of Li ₄ Ti ₅ 0 ₁₂ : one is to prepare lithium titanate into nano-lithium titanate material; the other is to dope conductive metal and carbon materials. Chinese patent (publication number: CN101630732A) discloses that the sol-gel method is used to mix a certain proportion of carbon nanotube dispersion liquid with titanium, lithium compound and doping element solution, and then heat and dry to obtain the gel precursor. A method for preparing lithium titanate composites coated with carbon nanotubes with a particle size of nanometers by lower sintering. Similarly, the Chinese patent (application number: 201110000627.3) also discloses a method of directly doping carbon nanotubes in lithium titanate to prepare negative electrode composite materials, thereby improving the battery rate performance. However, in the composite negative electrode material prepared by the above method, carbon nanotubes and lithium titanate are simply mixed together, and the distribution uniformity and binding force of carbon nanotubes on the surface of lithium titanate are poor, which greatly improves the rate performance of the battery. very limited.

Chinese patent (notification number: CN101969112A) discloses a method for preparing negative electrode materials. After mechanically mixing the negative electrode material and the catalyst at a mass ratio of 100: (0.1 to 5), they are added to a heating reaction device and passed through a carbon source gas. And by using the protective gas as the carrier gas, heat it up to 400-900°C and keep it warm for 1-72 hours, then cool it down to form a mixture of negative electrode materials, catalysts and carbon nanotubes; then mix the mixture with the oxidant in a mass ratio of 1:(1 ~100) into a reaction kettle, add water and stir to form a paste; then heat the paste to 50-400°C and react for 1-20 hours to obtain a composite negative electrode material coated with carbon nanotubes on the surface. However, the reaction process of this method is complicated, and the stability of the obtained negative electrode material is poor. The oxidation step will destroy the stable structure of lithium titanate itself, and ultimately affect the cycle performance of the battery.

Contents of the invention

The purpose of the present invention is to provide a preparation method of lithium titanate/carbon nanotube composite negative electrode material, so as to improve the rate performance and cycle performance of the battery.

In order to achieve the above object, the technical solution adopted in the present invention is:

A method for preparing a lithium titanate/carbon nanotube composite negative electrode material, the specific steps are as follows: add catalyst powder with a particle size of 30 to 100 nm into lithium titanate powder with a particle size of 0.3 to 10 μm and mix evenly, and mix the mixed powder in Heating to 600-800°C under a hydrogen atmosphere, then passing acetylene gas at a temperature of 800-1200°C, and then keeping the temperature constant for 24-48 hours, cooling the product after constant temperature to room temperature under the protection of an inert gas, and removing the catalyst.

The catalyst is iron, cobalt, nickel, iron nitrate, nickel nitrate, iron chloride or nickel chloride.

The weight ratio of the lithium titanate powder to the catalyst is lithium titanate powder:catalyst=10:(0.1-1).

The inert gas is nitrogen, argon or helium.

The lithium titanate powder can be prepared by conventional methods, or it can be commercially available. The present invention only provides a specific method for preparing lithium titanate powder, the steps are as follows: according to the molar ratio of lithium:titanium:dispersant=1:(1.2~2):(3~8) take lithium source, titanium source and Dispersant, after mixing, ball mill until the powder particle size is 0.5~5μm, dry, and under the protection of inert gas, calcinate the dried powder at 600~1000℃ for 1~48 hours, and ball mill the calcined powder until the particle size is 0.3~ Lithium titanate powder with a thickness of 10 μm is obtained.

Described lithium source is lithium carbonate, lithium acetate, lithium nitrate or lithium hydroxide.

The titanium source is titanium dioxide.

Described dispersant is dehydrated alcohol.

Beneficial effects of the present invention:

The present invention adopts the chemical vapor deposition method to grow carbon nanotubes on the surface of lithium titanate. Compared with directly doping carbon nanotubes in lithium titanate, it has the characteristics of uniform dispersion and strong binding force. At the same time, the grown carbon nanotubes are easier to The formation of a network structure on the surface of lithium titanate plays an important role in improving the structural stability of the battery under high-rate discharge conditions.

The lithium-ion battery of the present invention improves the contact probability with lithium titanate by utilizing the high conductivity of carbon nanotubes and the network structure formed therein, reduces internal resistance, reduces polarization, and at the same time, the larger specific surface area of carbon nanotubes can Improve the liquid absorption and liquid retention capacity of the negative electrode material, thereby improving the high rate discharge capacity of the battery and the cycle capacity of the battery.

In short, the composite anode material prepared by growing carbon nanotubes on the surface of lithium titanate by chemical vapor deposition can not only improve the conductivity and high rate discharge capacity of lithium titanate, but also improve the liquid absorption capacity and cycle stability of the battery. , which plays a good role in promoting the wide application of lithium titanate negative electrode materials; and the preparation method is simple, fast, good in stability and low in cost, and is suitable for large-scale production and application.

Description of drawings

Fig. 1 is the electron microscope picture that the embodiment of the present invention 1 prepares negative electrode material;

Fig. 2 is the rate discharge figure of lithium-ion battery in embodiment 1;

Fig. 3 is the cycle graph of the lithium ion battery in the embodiment and the comparative example.

Detailed ways

The present invention will be described in further detail below in conjunction with specific examples, but does not constitute any limitation to the present invention.

Example 1

In this example, the lithium titanate/carbon nanotube composite negative electrode material is prepared by the following method, and the specific steps are:

(1) Preparation of lithium titanate powder: According to the molar ratio of lithium: titanium: dispersant = 1:1.2:5, take lithium carbonate, titanium dioxide and absolute ethanol, mix them evenly and add them to the planetary ball mill at a speed of 400 rpm/ Wet ball milling for 48 hours to obtain a powder with a particle size of 2 μm. The powder was dried at a constant temperature of 100°C for 2 hours, and the dried powder was calcined at 800°C for 12 hours under the protection of argon, and the calcined powder was cooled. Take it out at 100°C, put it into an ultra-fine ball mill and mill it at a speed of 1000 rpm for 120 minutes to obtain lithium titanate powder with a particle size of 1 μm;

(2) Add an iron catalyst with a particle size of 50 nm to the lithium titanate powder with a particle size of 2 μm in step (1) and mix to obtain a mixed powder. The weight ratio of the lithium titanate powder to iron is lithium titanate powder: iron =10:0.5, put the mixed powder into the quartz tube reactor, and feed hydrogen into the reactor, and raise the temperature in the reactor to 600 at a rate of 10°C/min during the process of feeding hydrogen. ℃, then pass acetylene gas at 800℃ for 100 minutes, keep the temperature for 24 hours, cool the product in the reactor to room temperature under nitrogen atmosphere after constant temperature, wash with concentrated sulfuric acid, distilled water, and dry at 80℃ for 6 hours The lithium titanate/carbon nanotube composite negative electrode material can be obtained by ball milling. The surface electron micrograph is shown in Figure 1.

The negative electrode material of the lithium ion in this example adopts the lithium titanate/carbon nanotube composite negative electrode material prepared above, the positive electrode material is battery lithium iron phosphate, and the electrolyte is 1.0mol/LLiPF ₆ /EC+DEC (V _EC : V _DEC =1:1) (EC: Ethylene Carbonate, DEC: Diethyl Carbonate), the diaphragm is Celgard2300 diaphragm from the United States, and the performance of the prepared 2.5AH lithium-ion battery is shown in Tables 1 and 2 below, the rate discharge diagram and the cycle curve. See Figure 2 and Figure 3 for details.

Example 2

In this example, the lithium titanate/carbon nanotube composite negative electrode material is prepared by the following method, and the specific steps are:

(1) Preparation of lithium titanate powder: Take lithium nitrate, titanium dioxide and absolute ethanol according to the molar ratio of lithium: titanium: dispersant = 1:2:3, mix them evenly and add them to the planetary ball mill at a speed of 400 rpm/ Wet ball milling at a rotating speed of 48 hours to obtain a powder with a particle size of 5 μm. The powder was dried at a constant temperature of 100 ° C for 3 hours, and the dried powder was calcined at 1000 ° C for 24 hours under the protection of nitrogen. The calcined powder was cooled to Take it out at 100°C, then put it into an ultra-fine ball mill and mill it at a speed of 2000 rpm for 300 minutes to obtain lithium titanate powder with a particle size of 3 μm;

(2) Add a cobalt catalyst with a particle size of 100 nm to the lithium titanate powder with a particle size of 3 μm in step (1) and mix to obtain a mixed powder. The weight ratio of the lithium titanate powder to cobalt is lithium titanate powder:cobalt =10:1, put the mixed powder into the quartz tubular reactor, and feed hydrogen into the reactor, and raise the temperature in the reactor to 800 °C at a rate of 20 °C/min during the process of feeding hydrogen ℃, then pass acetylene gas at 1000℃ for 200 minutes, and keep the temperature constant for 24 hours. The lithium titanate/carbon nanotube composite negative electrode material can be obtained by ball milling.

The negative electrode material of the lithium ion in this example adopts the lithium titanate/carbon nanotube composite negative electrode material prepared above, the positive electrode material is battery lithium iron phosphate, and the electrolyte is 1.0mol/LLiPF ₆ /EC+DEC (V _EC : V _DEC =1:1) (EC: ethylene carbonate, DEC: diethyl carbonate), the diaphragm is Celgard 2300 diaphragm from the United States, the performance of the prepared 2.5AH lithium-ion battery is shown in Table 1 below, and the cycle curve is shown in Figure 3.

Example 3

In this example, the lithium titanate/carbon nanotube composite negative electrode material is prepared by the following method, and the specific steps are:

(1) Preparation of lithium titanate powder: Take lithium acetate, titanium dioxide and absolute ethanol according to the molar ratio of lithium: titanium: dispersant = 1:2:8, mix them evenly and add them to the planetary ball mill at a speed of 400 rpm/ Wet ball milling at a rotating speed of 48 hours to obtain a powder with a particle size of 0.5 μm. The powder was dried at a constant temperature at 100°C for 4 hours, and the dried powder was calcined at 600°C for 48 hours under the protection of helium. The calcined powder Cool to 100°C and take it out, then put it into an ultra-fine ball mill and mill at a speed of 1500 rpm for 200 minutes to obtain lithium titanate powder with a particle size of 0.3 μm;

(2) Add a nickel catalyst with a particle size of 30 nm to the lithium titanate powder with a particle size of 0.3 μm in step (1) and mix to obtain a mixed powder. The weight ratio of the lithium titanate powder to nickel is lithium titanate powder: Nickel=10:0.1, the mixed powder is added in the quartz tubular reactor, and hydrogen gas is passed into the reactor, and the temperature in the reactor is raised to 600°C, then pass acetylene gas at 900°C for 50 minutes, keep the temperature constant for 48 hours, cool the product in the reactor to room temperature under a nitrogen atmosphere after constant temperature, then wash with concentrated sulfuric acid, distilled water, and dry at 60°C for 8 hours After ball milling, the lithium titanate/carbon nanotube composite negative electrode material can be obtained.

The negative electrode material of the lithium ion in this example adopts the lithium titanate/carbon nanotube composite negative electrode material prepared above, the positive electrode material is battery lithium iron phosphate, and the electrolyte is 1.0mol/LLiPF ₆ /EC+DEC (V _EC : V _DEC =1:1) (EC: ethylene carbonate, DEC: diethyl carbonate), the diaphragm is Celgard 2300 diaphragm from the United States, the performance of the prepared 2.5AH lithium-ion battery is shown in Table 1 below, and the cycle curve is shown in Figure 3.

Example 4

In this example, the lithium titanate/carbon nanotube composite negative electrode material is prepared by the following method, and the specific steps are:

(1) Preparation of lithium titanate powder: Take lithium hydroxide, titanium dioxide and absolute ethanol according to the molar ratio of lithium: titanium: dispersant = 1:1.2:8, mix them evenly and add them to a planetary ball mill at a speed of 400 rpm Wet ball milling at a rotational speed of 48 hours to obtain a powder with a particle size of 0.5 μm. The powder was dried at a constant temperature at 100° C. for 1 hour, and the dried powder was calcined at 700° C. for 30 hours under the protection of argon. The calcined Cool the powder to 100°C and take it out, then put it into an ultra-fine ball mill and mill it at a speed of 2000 rpm for 200 minutes to obtain a lithium titanate powder with a particle size of 1 μm;

(2) Add iron nitrate catalyst with a particle size of 50nm to the lithium titanate powder with a particle size of 1 μm in step (1) and mix to obtain a mixed powder. : ferric nitrate=10:0.3, the mixed powder is added in the quartz tubular reactor, and hydrogen gas is passed into the reactor, and the temperature in the reactor is lowered at a speed of 10 °C/min during the process of feeding hydrogen gas. Raise to 1000°C, then pass acetylene gas at 850°C for 300 minutes, keep the temperature for 1 hour, cool the product in the reactor after constant temperature to room temperature under nitrogen atmosphere, then wash with concentrated sulfuric acid, distilled water, and dry at 60°C After 8 hours, the lithium titanate/carbon nanotube composite negative electrode material was obtained by ball milling.

The negative electrode material of the lithium ion in this example adopts the lithium titanate/carbon nanotube composite negative electrode material prepared above, the positive electrode material is battery lithium iron phosphate, and the electrolyte is 1.0mol/LLiPF ₆ /EC+DEC (V _EC : V _DEC =1:1) (EC: ethylene carbonate, DEC: diethyl carbonate), the diaphragm is Celgard 2300 diaphragm from the United States, the performance of the prepared 2.5AH lithium-ion battery is shown in Table 1 below, and the cycle curve is shown in Figure 3.

Example 5

In this example, the lithium titanate/carbon nanotube composite negative electrode material is prepared by the following method, and the specific steps are:

(1) Preparation of lithium titanate powder: Take lithium hydroxide, titanium dioxide and absolute ethanol according to the molar ratio of lithium: titanium: dispersant = 1:1.2:3, mix them evenly and add them to the planetary ball mill at a speed of 400 rpm Wet ball milling at a rotational speed of 48 hours to obtain a powder with a particle size of 5 μm. The powder was dried at a constant temperature of 100 ° C for 4 hours, and the dried powder was calcined at 700 ° C for 30 hours under the protection of argon. The calcined powder Cool to 100°C and take it out, then put it into an ultra-fine ball mill and mill at a speed of 2000 rpm for 200 minutes to obtain lithium titanate powder with a particle size of 10 μm;

(2) Add nickel-iron chloride catalyst with a particle size of 80 nm to the lithium titanate powder with a particle size of 10 μm in step (1) and mix to obtain a mixed powder. The weight ratio of the lithium titanate powder to nickel chloride is titanium Lithium acid powder: nickel chloride=10:0.5, the mixed powder is added in the quartz tubular reactor, and hydrogen gas is passed into the reactor, and the speed of 10 ℃/min is reacted in the process of passing into hydrogen gas. The temperature in the reactor was raised to 800°C, and then acetylene gas was introduced at a temperature of 1000°C for 60 minutes, and the temperature was kept constant for 24 hours. After the constant temperature, the product in the reactor was cooled to room temperature under a nitrogen atmosphere, and then washed with concentrated sulfuric acid and distilled water. , Dry at 60°C for 8 hours and ball mill to obtain the lithium titanate/carbon nanotube composite negative electrode material.

The negative electrode material of the lithium ion in this example adopts the lithium titanate/carbon nanotube composite negative electrode material prepared above, the positive electrode material is battery lithium iron phosphate, and the electrolyte is 1.0mol/LLiPF ₆ /EC+DEC (V _EC : V _DEC =1:1) (EC: ethylene carbonate, DEC: diethyl carbonate), the diaphragm is Celgard 2300 diaphragm from the United States, the performance of the prepared 2.5AH lithium-ion battery is shown in Table 1 below, and the cycle curve is shown in Figure 3.

Comparative example 1

The positive electrode material of lithium ions in this comparative example is pure lithium titanate, and the electrolyte is 1.0mol/LLiPF ₆ /EC+DEC (V _EC : V _DEC = 1:1) (EC: ethylene carbonate, DEC: diethyl carbonate ), the separator is the American Celgard2300 separator, the performance of the prepared 2.5AH lithium-ion battery is shown in Table 1 below, and the cycle curve is shown in Figure 3.

Comparative example 2

In this comparative example, the lithium titanate/carbon nanotube composite negative electrode material is prepared by the following method, and the specific steps are:

(1) Preparation of lithium titanate powder: Take lithium hydroxide, titanium dioxide and absolute ethanol according to the molar ratio of lithium: titanium: dispersant = 1:1.2:3, mix them evenly and add them to the planetary ball mill at a speed of 400 rpm Wet ball milling at a rotational speed of 48 hours to obtain a powder with a particle size of 5 μm. The powder was dried at a constant temperature of 100 ° C for 10 hours, and the dried powder was calcined at 700 ° C for 30 hours under the protection of argon. The calcined powder Cool to 100°C and take it out, then put it into an ultra-fine ball mill and mill at a speed of 2000 rpm for 200 minutes to obtain lithium titanate powder with a particle size of 10 μm;

(2) Add nickel-iron chloride catalyst with a particle size of 80 nm to the lithium titanate powder with a particle size of 10 μm in step (1) and mix to obtain a mixed powder. The weight ratio of the lithium titanate powder to nickel chloride is titanium Lithium acid powder: nickel chloride=10:0.5, the mixed powder is added in the quartz tubular reactor, and hydrogen gas is passed into the reactor, and the speed of 10 ℃/min is reacted in the process of passing into hydrogen gas. The temperature in the reactor was raised to 800°C, and then acetylene gas was introduced at 1000°C for 60 minutes, and the temperature was kept constant for 24 hours. After the constant temperature, the product in the reactor was cooled to room temperature under a nitrogen atmosphere, and then according to the mass ratio product:concentrated hydrochloric acid , mixed acid of hydrofluoric acid = 1:50, mixed with water, stirred into a paste, heated to 300°C at a heating rate of 5°C/min and reacted for 5 hours, stirring once every 1 hour during the reaction, and then the paste Move the paste into the centrifugal washing equipment, continue to add water to wash at the speed of 300r/min until the pH of the slurry is neutral, centrifugal dehydration to make the moisture content lower than 40%, and then dry at 100°C until the moisture content is lower than 0.01% Instantly.

The lithium ion negative electrode material of this comparative example adopts the lithium titanate/carbon nanotube composite negative electrode material prepared above, the positive electrode material is battery lithium iron phosphate, and the electrolyte is 1.0mol/LLiPF ₆ /EC+DEC (V _EC : V _DEC =1:1) (EC: ethylene carbonate, DEC: diethyl carbonate), the diaphragm is Celgard 2300 diaphragm from the United States, the performance of the prepared 2.5AH lithium-ion battery is shown in Table 1 below, and the cycle curve is shown in Figure 3.

Comparison of lithium-ion battery rate performance in the embodiment and comparative examples of table 1

The comparison of lithium-ion battery cycle performance in the embodiment of table 2 and comparative example

Claims (4)

1. the preparation method of a lithium titanate/carbon nano tube composite cathode material, it is characterized in that: concrete steps are as follows: be in the lithium titanate powder of 0.3 ~ 10 μm, add the catalyst fines mixing that particle diameter is 30 ~ 100nm at particle diameter, mixed-powder is heated to 600 ~ 800 DEG C under an atmosphere of hydrogen, then at temperature is 800 ~ 1200 DEG C, pass into acetylene gas, constant temperature 24 ~ 48 hours again, product after constant temperature is cooled to room temperature under inert gas shielding, remove catalyst and namely obtain the lithium titanate/carbon nano tube composite cathode material forming carbon nanotube network on lithium titanate surface,

Described catalyst is iron, cobalt, nickel, ferric nitrate, nickel nitrate, iron chloride or nickel chloride;

Described lithium titanate powder and the weight ratio of catalyst are lithium titanate powder: catalyst=10:(0.1 ~ 1);

The preparation process of described lithium titanate powder is as follows: be lithium according to mol ratio: titanium: dispersant=1:(1.2 ~ 2): (3 ~ 8) get lithium source, titanium source and dispersant; being milled to particle size after mixing is 0.5 ~ 5 μm; dry; under inert gas shielding, dried powder is calcined 1 ~ 48 hour at 600 ~ 1000 DEG C, the powder after calcining is milled to granularity and is 0.3 ~ 10 μm and namely obtains lithium titanate powder.

2. the preparation method of lithium titanate/carbon nano tube composite cathode material according to claim 1, is characterized in that: described lithium source is lithium carbonate, lithium acetate, lithium nitrate or lithium hydroxide.

3. the preparation method of lithium titanate/carbon nano tube composite cathode material according to claim 1, is characterized in that: described titanium source is titanium dioxide.

4. the preparation method of lithium titanate/carbon nano tube composite cathode material according to claim 1, is characterized in that: described dispersant is absolute ethyl alcohol.