CN107230780B - Lithium titanate composite electrode material and preparation method thereof - Google Patents

Abstract

The invention belongs to the technical field of battery materials, and particularly relates to a lithium titanate electrode material and a preparation method thereof. A coating layer is coated outside a lithium titanate negative electrode material, and the coating layer is ferrocene. The lithium titanate electrode material prepared by the method has good rate capability, can effectively inhibit gas generation of the material, has a first discharge specific capacity value of 170mAh/g, and is almost close to the theoretical specific capacity 175mAh/g of the material.

Description

A kind of lithium titanate composite electrode material and preparation method thereof

technical field

The invention belongs to the technical field of battery materials, and particularly relates to a lithium titanate composite electrode material and a preparation method thereof.

Background technique

The negative electrode material is one of the key materials of lithium-ion batteries. At present, most of the negative electrode materials used in lithium-ion batteries are lithium-inserted graphitized carbon materials. However, such materials have some problems in practical applications. Low, the volume changes during the charging and discharging process, and it is easy to form lithium dendrites, causing a short circuit, and the decomposition of the electrolyte poses a safety hazard. In contrast, lithium titanate with spinel structure has a theoretical capacity of 175mAh/g, and lithium ion insertion and de-intercalation has little effect on the material structure during charging and discharging, and is called a "zero-strain" material. The discharge platform is good, the platform capacity can reach more than 90% of the discharge capacity, the cycle performance is good, it does not react with the electrolyte, the preparation method is simple, and the cost is low. Therefore, at present, spinel-type lithium titanate has become an extremely promising negative electrode material for lithium-ion batteries due to its excellent safety properties and long cycle life.

Although lithium titanate has many outstanding advantages as an anode material for lithium ion batteries, and the chemical diffusion coefficient of lithium ions at room temperature is 2×10 ^-8 cm ² /s, which is an order of magnitude larger than that of carbon anodes, its intrinsic conductivity low, only 10 ^-9 S/cm, which is a typical insulator with poor conductivity, resulting in poor performance and rapid specific capacity decay during high-rate charge and discharge, and unsatisfactory high-current discharge performance. The electrical conductivity of the material can be improved by doping to obtain better fast charge-discharge performance and cycle performance. The Chinese invention patent "An yttrium-modified lithium titanate negative electrode material and its preparation method" (CN102780005A), this patent uses a solid-phase method to prepare a yttrium-modified lithium titanate negative electrode material, which has good electrochemical performance and Higher Coulombic efficiency. The Chinese invention patent "A lanthanum-doped lithium titanate negative electrode material and its preparation method" (CN 102637864A), the patent uses a solid-phase method to prepare a lanthanum-doped lithium titanate negative electrode material, and refines it by doping a trace amount of lanthanum. The crystal grains improve the electrochemical performance of lithium titanate. The above two methods of doping a single metal ion have achieved beneficial effects, but the problem of uneven mixing of raw materials is likely to occur when the solid-phase method is used for preparation, which affects the electrochemical performance. The Chinese invention patent "A preparation method of three-dimensional porous graphene-doped and coated lithium titanate composite negative electrode material" (CN102646810A), discloses a three-dimensional porous graphene-doped and coated lithium titanate composite material preparation method , the high-rate electrochemical performance of lithium titanate anode materials was effectively improved by doping carbon materials. However, the three-dimensional porous graphene material described in this patent is processed by hydrothermal method, which still cannot effectively suppress the stacking of graphene sheets and the agglomeration phenomenon during sintering, and will generate gas in practical applications, which will lead to The cycle performance is attenuated, which limits its performance to a certain extent.

Therefore, to develop a simple preparation method, excellent electrical conductivity, excellent electrochemical performance at high rates, and can effectively suppress gas generation of lithium titanate anode materials, lithium titanate composite anode materials with good electrochemical cycle stability are Technical problems in the field.

SUMMARY OF THE INVENTION

The purpose of the present invention is to solve the above-mentioned technical problems, and to provide a lithium titanate negative electrode material with good rate performance and effectively suppressing material gas production; the present invention also provides a preparation method of a lithium titanate negative electrode material.

For achieving the above object, the technical scheme adopted in the present invention is:

A lithium titanate composite electrode material, which is coated with a coating layer on the outside of the lithium titanate negative electrode material, and the coating layer is a mixture of carbon and iron oxide.

Further, the coating layer accounts for 1-3% of the total weight of the lithium titanate negative electrode material.

Further, the composition of the lithium titanate negative electrode material is: Li ₄ Ti _5-x Nb _x O _12-Y Br _Y . where 0<X<1, 0<Y<1.4.

A preparation method of the above-mentioned electrode material, comprising the following steps:

(1) According to the composition of the lithium titanate negative electrode material, calculate and weigh the required lithium acetate, tetrabutyl titanate and niobium hydroxide, and set the lithium acetate and cetyltrimethylammonium bromide to 0.3 according to the molar ratio. The ratio of -0.5:0.02-0.2:1 is dissolved in absolute ethanol, stirred and mixed evenly to obtain mixture A;

(2) The mixture A is heated to 70-90°C, and niobium hydroxide is slowly added dropwise to it under stirring conditions, and the dropwise addition time is 1-3h;

(3) Dissolve tetrabutyl titanate in absolute ethanol at a molar ratio of 0.2-0.5:1, and then add the reaction mixture obtained in step (2) to the mixture of tetrabutyl titanate under stirring conditions. In anhydrous ethanol solution, the obtained mixed liquid is stirred and evaporated under the condition of 80-90 ℃ to obtain gel;

(4) Add ferrocene to the above gel, and use a three-dimensional high-speed oscillating ball mill to ball-mill and mix the raw materials. The ball-milling time is 1-2 hours, and the oscillation frequency is 800-1100 rpm. , calcined for 24-36 h under the protection of inert gas, and cooled to obtain the composite lithium titanate electrode material.

Further, in step (1), lithium acetate and cetyl trimethyl ammonium bromide are dissolved in absolute ethanol according to a molar ratio of 0.3:0.1:1.

Further, in step (3), the molar ratio of tetrabutyl titanate to absolute ethanol is 0.3.

Further, in step (4), a dual-temperature zone rotary furnace is used for calcination, the rotating speed of the furnace tube is set to be less than 3 rpm, and the intermittent time is 1 minute.

The advantages and positive effects that the present invention has are:

(1) Through the co-doping method of metal ion Nb ⁵⁺ and non-metal ion Br ^- , the conductivity of lithium titanate bulk material is more effectively improved than single-ion doping, and the charge-discharge specific capacity and cycle performance are more significantly improved. promotion. .

(2) Co-coating with carbon and metal oxides, on the one hand, takes into account the advantages of carbon coating to improve electrical conductivity, and on the other hand, the role of metal oxide coating to strengthen the coating layer can not affect or even improve titanic acid. While the lithium body material is conductive, it can also block the contact between the electrolyte and the lithium titanate body material through a strong mixed coating layer, inhibit the decomposition of the electrolyte, and reduce the generation of gas. Compared with single carbon coating and single metal oxide coating, the mixed coating of carbon and metal oxide has more obvious advantages in improving the electrochemical performance of lithium titanate anode material.

(3) The raw material is sintered in a double-temperature zone rotary furnace, and the prepared electrode material has better uniformity, the particle size of the material is more uniform, and the phenomenon of agglomeration is avoided.

(4) Adding a small amount of cetyltrimethylammonium bromide in the preparation process can improve the cycle performance and the first discharge specific capacity of the lithium titanate negative electrode material. The electrode material prepared by the present invention has the first discharge specific capacity value. It is 170mAh/g, which is almost close to the theoretical specific capacity of the material.

Description of drawings

Fig. 1 Electron microscope image of uncoated electrode material (Comparative Example 1);

Fig. 2 Electron microscope image of the material obtained in Example 1;

Fig. 3 Electron microscope image of the material obtained in Example 2;

Fig. 4 Electron microscope image of the material obtained in Example 3.

Detailed ways

Below by embodiment, the present invention is specifically described and illustrated:

Example 1

A lithium titanate composite electrode material, the coating layer is ferrocene, the coating layer accounts for 1% of the total weight of the lithium titanate negative electrode material, and the composition of the lithium titanate negative electrode material is: Li ₄ Ti _4.9 Nb _0.1 O _{11.97Br0.03 .}

The preparation method of this material includes the following steps:

(1) According to the composition of the lithium titanate negative electrode material, calculate and weigh the required lithium acetate, tetrabutyl titanate and niobium hydroxide, and set the lithium acetate and cetyltrimethylammonium bromide to 0.3 according to the molar ratio. : Dissolve in absolute ethanol in a ratio of 0.02:1, stir and mix evenly to obtain mixture A;

(2) The mixture A was heated to 70°C, and niobium hydroxide was slowly added dropwise to it under stirring conditions, and the dropwise addition time was 3h;

(3) Dissolve tetrabutyl titanate in absolute ethanol in a molar ratio of 0.2:1, and then add the reaction mixture obtained in step (2) to anhydrous tetrabutyl titanate under stirring conditions. In the ethanol solution, the obtained mixed liquid was stirred and evaporated at 90°C to obtain a gel;

(4) Add ferrocene to the above gel, use a three-dimensional high-speed oscillating ball mill to ball-mill and mix the raw materials, the ball-milling time is 1 hour, the oscillation frequency is 1100 rpm, and then calcined at 600 ° C under the protection of inert gas 36h, cooling to obtain the lithium titanate electrode material.

A lithium ion battery was prepared by using the lithium titanate material prepared in this example as an active material. Using N-methylpyrrolidone (NMP) as a solvent, the lithium titanate material prepared in Example 2, the conductive agent acetylene black and the binder polyvinylidene fluoride (PVDF) were stirred and mixed uniformly in a mass ratio of 8:1:1 The slurry was then prepared, and then coated on Al foil, dried, and then cold-pressed and punched into small discs with a diameter of 14 mm. The prepared small disc is used as the negative electrode, the lithium metal sheet is used as the counter electrode, the Celgard 2400 microporous polypropylene film is used as the separator, and the 1M LiPF6/(EC+DEC) (1:1, volume ratio) solution is used as the electrolyte assembly. into a 2032 button half battery.

The cyclic voltammetry test and the constant current charge-discharge test were then carried out. The results showed that the first discharge specific capacity reached 169mAh/g. After 500 cycles at 1C rate, the electrochemical performance of the material basically did not decay, and the stability was good.

Example 2

A lithium titanate composite electrode material, the coating layer is ferrocene, the coating layer accounts for 3% of the total weight of the lithium titanate negative electrode material, and the lithium titanate negative electrode material is composed of: Li ₄ Ti _4.1 Nb _0.9 O _{10.4Br 1.6} .

The preparation method of this material includes the following steps:

(1) According to the composition of the lithium titanate negative electrode material, calculate and weigh the required lithium acetate, tetrabutyl titanate and niobium hydroxide, and dissolve the lithium acetate and cetyltrimethylammonium bromide according to the molar ratio as Dissolve in absolute ethanol in a ratio of 0.5:0.2:1, stir and mix evenly to obtain mixture A;

(2) The mixture A was heated to 90°C, and niobium hydroxide was slowly added dropwise to it under stirring for 1 h;

(3) Dissolve tetrabutyl titanate in absolute ethanol at a molar ratio of 0.5:1, and then add the reaction mixture obtained in step (2) to anhydrous tetrabutyl titanate under stirring conditions. In the ethanol solution, the obtained mixed liquid was stirred and evaporated at 80°C to obtain a gel;

(4) Add ferrocene to the above gel, and use a three-dimensional high-speed oscillating ball mill to ball-mill and mix the raw materials. The ball-milling time is 2 hours, the oscillation frequency is 800 rpm, and then calcined at 800 ° C under the protection of inert gas. 24h, cooling to obtain the lithium titanate electrode material.

A lithium ion battery was prepared by using the lithium titanate material prepared in this example as an active material. The preparation method is the same as in Example 1.

The cyclic voltammetry test and the constant current charge-discharge test were then carried out. The results showed that the first discharge specific capacity reached 168mAh/g, and the electrochemical performance of the material was basically unchanged after 500 cycles at a rate of 1C, and the stability was good.

Example 3

A lithium titanate composite electrode material, the coating layer is ferrocene, the coating layer accounts for 2% of the total weight of the lithium titanate negative electrode material, and the lithium titanate negative electrode material is composed of: Li ₄ Ti _4.5 Nb _0.5 O _{11Br 1} .

The preparation method of this material includes the following steps:

(1) Calculate and weigh the required lithium acetate, tetrabutyl titanate and niobium hydroxide according to the composition of the lithium titanate negative electrode material, and set the lithium acetate and cetyltrimethylammonium bromide to 0.4 according to the molar ratio. : The ratio of 0.1:1 is dissolved in absolute ethanol, stirred and mixed evenly to obtain mixture A;

(2) The mixture A was heated to 80°C, and niobium hydroxide was slowly added dropwise to it under stirring conditions, and the dropwise addition time was 2h;

(3) Dissolve tetrabutyl titanate in absolute ethanol at a molar ratio of 0.4:1, and then add the reaction mixture obtained in step (2) to anhydrous tetrabutyl titanate under stirring conditions. In the ethanol solution, the obtained mixed liquid was stirred and evaporated at 85°C to obtain a gel;

(4) Add ferrocene to the above gel, and use a three-dimensional high-speed oscillating ball mill to ball-mill and mix the raw materials. The ball-milling time is 1.5 hours, the oscillation frequency is 1000 rpm, and then calcined at 750 ° C under the protection of inert gas. 32h, cooling to obtain the lithium titanate electrode material.

A lithium ion battery was prepared by using the lithium titanate material prepared in this example as an active material. The preparation method is the same as in Example 1.

The cyclic voltammetry test and the constant current charge-discharge test were then carried out. The results showed that the first discharge specific capacity reached 170mAh/g, and the electrochemical performance of the material was basically unchanged after 500 cycles at a rate of 1C, and the stability was good.

Comparative Example 1

No, the corresponding steps are removed in the preparation process, and other steps and compositions are the same as in Example 3.

A lithium ion battery was prepared by using the lithium titanate material prepared in this example as an active material. The preparation method is the same as in Example 1.

Then, cyclic voltammetry test and constant current charge-discharge test were carried out. The results showed that the first discharge specific capacity reached 151mAh/g, and the capacity retention rate of the material after 500 cycles at 1C rate was 77%.

Comparative Example 2

No niobium doping was performed, and corresponding steps were removed in the preparation process, and other steps and compositions were the same as those in Example 3.

A lithium ion battery was prepared by using the lithium titanate material prepared in this example as an active material. The preparation method is the same as in Example 1.

The cyclic voltammetry test and the constant current charge-discharge test were then carried out. The results showed that the first discharge specific capacity reached 155mAh/g, and the capacity retention rate of the material after 500 cycles at 1C rate was 68%.

Comparative Example 3

Cetyltrimethylammonium bromide is not used in the preparation process, and its composition and preparation process are the same as in Example 3.

A lithium ion battery was prepared by using the lithium titanate material prepared in this example as an active material. The preparation method is the same as in Example 1.

Then, cyclic voltammetry test and constant current charge-discharge test were carried out. The results showed that the first discharge specific capacity reached 158mAh/g, and the capacity retention rate of the material after 500 cycles at 1C rate was 70%.

It can be seen from Figures 1-4 that the surfaces of the materials prepared in Examples 1-3 of the present invention have a uniform coating layer.

Flatulence test: The lithium titanate negative electrode material prepared by the above-mentioned Example 1-3 and Comparative Example 1-3 was used as the negative electrode material, and the commercial ternary electrode material was the positive electrode material, which were respectively made into the positive and negative electrode sheets of the battery, and then The above-mentioned positive and negative electrode sheets and separators were wound into a battery cell, injected with electrolyte, and assembled into a soft-pack battery to investigate its flatulence behavior and electrochemical performance. The results show that after 2000 times of charging and discharging at a high rate of 5C, the flatulence phenomenon of the pouch battery prepared by using the materials of Examples 1-3 is obviously suppressed, and the thickness expansion of the pouch battery is about 5% on average, which is significantly smaller than that of Comparative Example 1. -3 20% of the pouch battery assembled as negative electrode material.

Claims (6)

1. A lithium titanate composite electrode material is characterized in that a coating layer is coated outside a lithium titanate negative electrode material, and the coating layer is a mixture of carbon and iron oxide;

the method comprises the following steps:

(1) according to the composition of the lithium titanate negative electrode material, calculating and weighing required lithium acetate, tetrabutyl titanate and niobium hydroxide, wherein the molar ratio of the lithium acetate to the hexadecyl trimethyl ammonium bromide is 0.3-0.5: dissolving in anhydrous ethanol at a ratio of 0.02-0.2:1, stirring and mixing to obtain mixture A;

(2) heating the mixture A to 70-90 ℃, slowly dripping the niobium hydroxide into the mixture A under the stirring condition, wherein the dripping time is 1-3 h;

(3) dissolving tetrabutyl titanate in absolute ethyl alcohol according to the molar ratio of 0.2-0.5:1, then adding the reaction mixture obtained in the step (2) into an absolute ethyl alcohol solution of tetrabutyl titanate under the condition of stirring, and stirring and evaporating the obtained mixed liquid at the temperature of 80-90 ℃ to obtain gel;

(4) adding ferrocene into the gel, performing ball milling and mixing on the raw materials by adopting a three-dimensional high-speed oscillation ball mill for 1-2 hours at a shimmy frequency of 800-1100 r/min, calcining for 24-36 hours at the temperature of 600-800 ℃ under the protection of inert gas, and cooling to obtain the lithium titanate composite electrode material.

2. The electrode material as claimed in claim 1, wherein the coating layer comprises 1-3% by weight of the lithium titanate negative electrode material.

3. The electrode material as claimed in claim 1, wherein the composition of the lithium titanate negative electrode material is: li₄Ti_5-xNb_xO_12-yBr_yWherein x is more than 0 and less than 1, and y is more than 0 and less than 1.

4. The electrode material as claimed in claim 1, wherein the lithium acetate and cetyltrimethylammonium bromide in step (1) are dissolved in anhydrous ethanol in a molar ratio of 0.3:0.1: 1.

5. The electrode material according to claim 1, wherein the molar ratio of tetrabutyl titanate to absolute ethyl alcohol in step (3) is 0.3.

6. The electrode material according to claim 1, wherein the calcination is performed in step (4) by using a rotary kiln with two temperature zones, wherein the rotation speed of the kiln tube is set to be less than 3 rpm, and the intermittent time is set to be 1 minute.

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