CN111732122A - A lithium ion battery based on MIL-125 (Ti) lithium titanate negative electrode material and preparation method thereof - Google Patents

Abstract

The invention discloses a lithium titanate negative electrode material based on MIL-125 (Ti) for a lithium ion battery. In the negative electrode material, the metal-organic framework MIL-125(Ti) is firstly pyrolyzed into disc-shaped TiO ₂ as an initial template, and then the disc-shaped TiO ₂ is reacted with a lithium source to obtain a lithium titanate precursor through solvothermal reaction. The lithium titanate precursor is then calcined to obtain a lithium titanate negative electrode material. In the present invention, by introducing the metal-organic framework as the initial template, the obtained disc-shaped lithium titanate negative electrode material has a large specific surface area, so that the lithium titanate can be better combined with the electrolyte, and the transmission channel of lithium ions in the lithium titanate is increased. and lithium storage sites to improve the electronic conductivity and ionic conductivity, improve the output power density of the battery, and also improve the structural stability of the lithium titanate material, resulting in better cyclability, higher capacity and higher energy density. Large lithium titanate anode material.

Description

A lithium ion battery based on MIL-125 (Ti) lithium titanate anode material and its preparation backup method

technical field

The invention belongs to the technical field of battery materials, and in particular relates to a lithium titanate negative electrode material based on MIL-125 (Ti) for lithium ion batteries and a preparation method thereof.

Background technique

Lithium-ion batteries were successfully developed and commercialized by SONY in Japan at the beginning of the 20th century. After more than a century of exploration and development, the current lithium-ion batteries can reach 100-150W·h·kg ^-1 mass specific energy. , the volume specific energy can reach 240-253W·h·L ^-1 , which is higher than the traditional nickel-cadmium batteries and nickel-hydrogen batteries, and the average working voltage is as high as 3.6V, so lithium-ion batteries are considered to be the most promising in the future. one of the batteries. At present, commercial lithium-ion battery anode materials mainly use carbon materials, including graphite-like carbon materials and amorphous carbon materials. Although carbon anode materials have been successfully used in lithium-ion batteries, for the first time, they have low coulombic efficiency and large volume changes, and organic solvents will co-embedded graphite sheets along with lithium ions, resulting in the gradual exfoliation of graphite materials. In order to overcome the defects of carbon materials, people have begun to study various new anode materials to replace carbon materials. Among them, lithium titanate is one of the most attractive anode materials for lithium-ion batteries, which is worthy of in-depth research and discussion. The lithium titanate anode material has a stable structure and almost no volume change during charging and discharging. It is called a "zero-strain" material, so the cycle performance is very good, the service life is long, and the discharge platform is stable and the Coulombic efficiency is high. But at the same time, it also has disadvantages such as low specific capacity, poor conductivity, and poor rate performance.

At present, the synthesis methods of lithium titanate mainly include high-temperature solid-phase method, sol-gel method, microwave synthesis method, and hydrothermal/solvothermal method. The research of lithium titanate materials focuses on the improvement of composite modification and preparation process.

Lithium titanate anode material mainly has the following advantages: (1) good safety: the potential of lithium titanate is higher than that of metal lithium, and no lithium dendrites will be generated during the charging/discharging process; (2) it is applicable at normal temperature : The charge/discharge can be safely completed at minus 30℃-60℃; (3) Good cycle performance: It has the characteristics of "zero strain", and there will be no passivation reaction during the battery charge/discharge process (the formation of SEI film) ) occurs, and the capacity retention rate is still very high after tens of thousands of charge-discharge cycles; (4) It can ensure the rapid charge/discharge of the battery: compared with graphite electrodes, lithium titanate has a much higher ion mobility for battery operation. . However, it also has disadvantages such as low electrical conductivity and poor rate performance.

SUMMARY OF THE INVENTION

Aiming at the poor repeatability and rate performance of the lithium titanate negative electrode material, the invention provides a lithium titanate negative electrode material based on MIL-125 (Ti) for a lithium ion battery with simple process, high safety and good stability, and a preparation method thereof. .

In order to achieve the above object, the present invention provides the following technical solutions:

A lithium titanate anode material based on MIL-125(Ti) for lithium ion batteries, the metal-organic framework MIL-125(Ti) is used as an initial template to pyrolyze into disc-shaped TiO ₂ , and then the disc-shaped TiO ₂ The lithium titanate precursor is obtained by reacting with a lithium source through a solvothermal method, and finally the lithium titanate precursor is calcined to obtain a lithium titanate negative electrode material.

A preparation method of a lithium ion battery based on MIL-125 (Ti) lithium titanate negative electrode material, comprising the following steps:

(1) at first respectively take by weighing terephthalic acid and measure N, N-dimethylformamide, methanol and tetraisopropyl titanate in a beaker, after stirring and mixing, it is placed in a reactor to carry out solvothermal reaction; then centrifuge, wash, and dry to obtain white powder MIL-125(Ti); then pyrolyze the white powder MIL-125(Ti) in a resistance furnace to obtain white TiO ₂ powder;

(2) The lithium source and the white _TiO powder prepared in step (1) are placed in ethanol and stirred, and when the solution is stirred to be milky white, it is transferred to a reactor and placed in an oven for solvothermal reaction, and after cooling, centrifugation, washing and drying to obtain a lithium titanate precursor material;

(3) The lithium titanate precursor material prepared in step (2) is calcined in a resistance furnace to obtain a disc-shaped lithium titanate negative electrode material.

Preferably, in step (1), the MIL-125(Ti) is a titanium-containing metal-organic framework compound Ti ₈ O ₈ (OH) ₄ (O ₂ CC ₆ H ₄ -CO ₂ ) ₆ .

Preferably, in step (1), the temperature of the solvothermal reaction is 140-160° C., the reaction time is 23-25 hours, the drying temperature is 65-75° C., the drying time is 8-12 hours, and the temperature of pyrolysis is 370-120° C. 390℃, the pyrolysis time is 4.5-5.5 hours.

Preferably, the centrifugation conditions in step (1) are 3-4 times of centrifugation at a rotational speed of 7000-8000 rpm/5 minutes.

Preferably, the lithium source in step (2) is one or more of lithium nitrate, lithium acetate, lithium carbonate and lithium hydroxide.

Preferably, the molar ratio of lithium/titanium in the lithium source and the white TiO ₂ powder in step (2) is 0.84-0.92.

Preferably, the temperature of the solvothermal reaction in step (2) is 175-185° C., and the time is 17-19 hours.

Preferably, in step (2), the centrifugation conditions are 4-6 times of centrifugation at a rotational speed of 7000-8000 rpm/5 minutes, and the drying conditions are drying at 55-65° C. for 5-8 hours.

Preferably, in step (3), the calcination temperature of the lithium titanate precursor material is 650-750° C., and the calcination time is 6-10 hours.

Compared with the prior art, the advantages of the present invention are:

1. The lithium titanate negative electrode material based on MIL-125 (Ti) of the present invention is a disc-shaped lithium titanate negative electrode material with better cycle performance and better rate performance.

2. The present invention is simple and easy to implement, has high production efficiency, reduces production steps, and saves production costs. Compared with materials without modification, the battery capacity, rate performance and cycle performance are greatly improved.

3. The disc-shaped lithium titanate anode material obtained by solvothermal method has better particle distribution and morphology characteristics. At the same time, it has a larger specific surface area, can better combine with the electrolyte, and increase the transport channels and lithium storage sites of lithium titanate, thereby improving the cycle performance and rate performance of lithium ion batteries.

Description of drawings

Figure 1 shows a schematic diagram of the synthesis of disc-shaped lithium titanate

FIG. 2 shows the XRD pattern of lithium titanate (Li ₄ Ti ₅ O ₁₂ ).

Figure 3 shows the microscopic topography of (a) MIL-125(Ti), (b) TiO ₂ , (c) lithium titanate precursor and (d) lithium titanate.

Figure 4 shows the first charge-discharge curves of disk-shaped lithium titanate under hydrothermal and solvothermal conditions at 0.2C.

Figure 5 shows the cycle performance diagrams of the lithium titanate anode materials synthesized by the hydrothermal method and the solvothermal method.

Detailed ways

In order to further understand the content features and beneficial effects of the present invention, the present invention will be described in further detail below through specific examples and in conjunction with the accompanying drawings.

Example 1

In this embodiment, the hydrothermal preparation method of the lithium ion battery based on the MIL-125 (Ti) lithium titanate negative electrode material includes the following steps:

(1) First weigh 1.5g of terephthalic acid and 27ml of DMF (nitrogen, nitrogen-dimethylformamide), 3ml of methanol is placed in a beaker, stir and mix well, add 0.78ml of tetratitanate to it with a micropipette Isopropyl ester, then the above mixed solution was transferred into a 50ml reaction kettle, kept at 150 ° C for 24 hours; then placed in a centrifuge tube for 3 times at 7000 rpm/5 minutes, and finally dried at 70 ° C in a vacuum drying box for 10 hours to obtain MIL-125(Ti) white powder;

(2) pyrolyze MIL-125(Ti) in a resistance furnace at 380°C for 5 hours to obtain _TiO2 white powder;

Subsequently, according to the molar ratio of lithium/titanium, Li:Ti=0.88, respectively weigh TiO ₂ and LiOH·H ₂ O obtained by sufficient pyrolysis; : water = 1: 1) as a solvent, stir well and put it in an oven for 18 hours under solvothermal heat at 180°C, then centrifuge the obtained hydrated lithium titanate at 8000r/3min for 4 times, and calcinate at a high temperature of 700°C in a resistance furnace after drying 8 hours to obtain the final disc-shaped lithium titanate white powder;

The prepared disc-shaped lithium titanate was uniformly mixed with acetylene black and polyvinylidene fluoride (PVDF) in a mass ratio of 8:1:1, rolled into a film with a thickness of 120 μm, and dried in vacuum at 120 °C for 10 h. Negative electrode of the experimental half-cell; using 1 mol/LLiPF ₆ /ethylene carbonate (EC)-dimethyl carbonate (DMC) (volume ratio of EC to DMC 1:1) electrolyte, in a dry argon-filled glove box In , the lithium metal sheet is used as the negative electrode to assemble the battery. The button battery with the lithium titanate prepared in this example as the positive electrode and the lithium sheet as the negative electrode, in the voltage range of 1-2.5V, is charged at a constant current-constant voltage at a rate of 0.2C, and discharged at a constant current at a rate of 0.2C. The first discharge specific capacity was 172.035mAhg ^-1 , but after 20 cycles the capacity was 165.811mAhg ^-1 .

Example 2

In this embodiment, the solvothermal preparation method of the lithium ion battery based on the MIL-125(Ti) lithium titanate negative electrode material, the synthesis schematic diagram of lithium titanate is shown in Figure 1, including the following steps:

(1) First weigh 1.5g of terephthalic acid and 27ml of DMF (nitrogen, nitrogen-dimethylformamide), 3ml of methanol is placed in a beaker, stir and mix well, add 0.78ml of tetratitanate to it with a micropipette Isopropyl ester, then the above mixed solution was transferred into a 50ml reaction kettle, kept at 150 ° C for 24 hours; then placed in a centrifuge tube for 3 times at 7000 rpm/5 minutes, and finally dried at 70 ° C in a vacuum drying box for 10 hours to obtain MIL-125(Ti) white powder;

(2) pyrolyze MIL-125(Ti) in a resistance furnace at 380°C for 5 hours to obtain _TiO2 white powder;

Subsequently, according to the molar ratio of lithium/titanium, Li:Ti=0.88, respectively weigh TiO ₂ and LiOH·H ₂ O obtained by sufficient pyrolysis; After stirring evenly, put it into an oven under solvothermal heat at 180°C for 18 hours, then centrifuge the obtained hydrated lithium titanate at 8000 r/3min for 4 times, and calcinate at a high temperature of 700°C for 8 hours in a resistance furnace after drying to obtain the final disc-shaped lithium titanate white powder;

The X-ray diffraction pattern of the disc-shaped lithium titanate prepared in the experiment is shown in FIG. 2 . It can be seen from Figure 2 that the crystallinity of the sample is good, and all diffraction peaks are consistent with spinel Li ₄ Ti ₅ O ₁₂ (JCPDS card number 49-0207). The crystallinity after calcination is very good, and substantially no heterogeneity exists. The combination of TiO ₂ and LiOH·H ₂ O is excellent, and it has good crystallinity driven by sintering. By calcining the solvothermal product in air, no peaks for carbon and _{TiO2 were} detected in the _{Li4Ti5O12 sample} . Therefore, pure Li ₄ Ti ₅ O ₁₂ can be obtained by this method.

The prepared disc-shaped lithium titanate was uniformly mixed with acetylene black and polyvinylidene fluoride (PVDF) in a mass ratio of 8:1:1, rolled into a film with a thickness of 120 μm, and dried in vacuum at 120 °C for 10 h. Negative electrode of the experimental half-cell; using 1 mol/LLiPF ₆ /ethylene carbonate (EC)-dimethyl carbonate (DMC) (volume ratio of EC to DMC 1:1) electrolyte, in a dry argon-filled glove box In , the lithium metal sheet is used as the negative electrode to assemble the battery. The button battery with the lithium titanate prepared in this example as the positive electrode and the lithium sheet as the negative electrode, in the voltage range of 1-2.5V, is charged at a constant current-constant voltage at a rate of 0.2C, and discharged at a constant current at a rate of 0.2C. The first discharge specific capacity was 179.112mAhg ^-1 , but after 20 cycles the capacity was 175.408mAhg ^-1 . Compared with Example 1, the solvothermal method obtained a higher specific capacity for the first charge at the same rate, as shown in Figure 4. And it can be seen from Figure 5 that the products synthesized by the solvothermal method have better cycle performance.

Claims (10)

1. A lithium titanate negative electrode material based on MIL-125(Ti) of a lithium ion battery is characterized in that a metal-organic framework MIL-125(Ti) is used as an initial template to be pyrolyzed into disc-shaped TiO₂Then the disc-shaped TiO is put into₂And reacting with a lithium source by a solvothermal method to obtain a lithium titanate precursor, and finally calcining the lithium titanate precursor to obtain the lithium titanate cathode material.

2. A preparation method of a lithium titanate negative electrode material of a lithium ion battery based on MIL-125(Ti) is characterized by comprising the following steps:

(1) firstly, respectively weighing terephthalic acid and N, N-dimethylformamide, methanol and tetraisopropyl titanate in a beaker, uniformly stirring and mixing, and then placing in a reaction kettle for solvothermal reaction; then centrifuging, washing and drying the mixture to obtain white powder MIL-125 (Ti); then pyrolyzing white powder MIL-125(Ti) in a resistance furnace to obtain white TiO₂Powder;

(2) mixing a lithium source and the white TiO prepared in the step (1)₂Placing the powder into ethanol for stirring, transferring the solution into a reaction kettle when the solution is stirred to be milk white, placing the solution into an oven for solvothermal reaction, cooling, centrifuging, washing and drying to obtain a lithium titanate precursor material;

(3) and (3) placing the lithium titanate precursor material prepared in the step (2) in a resistance furnace to calcine to obtain the disc-shaped lithium titanate negative electrode material.

3. The method for preparing the MIL-125(Ti) -based lithium titanate negative electrode material of the lithium ion battery according to claim 2, wherein the MIL-125(Ti) in the step (1) is a titanium-containing metal-organic framework compound Ti₈O₈(OH)₄(O₂C-C₆H₄-CO₂)₆。

4. The method for preparing the MIL-125(Ti) -based lithium titanate negative electrode material of the lithium ion battery as claimed in claim 2, wherein the temperature of the solvothermal reaction in the step (1) is 140-160 ℃, the reaction time is 23-25 hours, the drying temperature is 65-75 ℃, the drying time is 8-12 hours, the pyrolysis temperature is 370-390 ℃, and the pyrolysis time is 4.5-5.5 hours.

5. The method for preparing the MIL-125(Ti) -based lithium titanate negative electrode material of the lithium ion battery as claimed in claim 2, wherein the centrifugation condition in the step (1) is centrifugation 3-4 times at 7000-8000 rpm.

6. The method for preparing the MIL-125(Ti) -based lithium titanate negative electrode material of the lithium ion battery according to claim 2, wherein the lithium source in the step (2) is one or more of lithium nitrate, lithium acetate, lithium carbonate and lithium hydroxide.

7. The method for preparing MIL-125(Ti) -based lithium titanate negative electrode material of lithium ion battery according to claim 2, wherein the lithium source and white TiO in the step (2)₂The lithium/titanium molar ratio in the powder is between 0.84 and 0.92.

8. The method for preparing the MIL-125(Ti) -based lithium titanate negative electrode material of the lithium ion battery as claimed in claim 2, wherein the temperature of the solvothermal reaction in the step (2) is 175-185 ℃ and the time is 17-19 hours.

9. The method for preparing the MIL-125(Ti) -based lithium titanate negative electrode material of the lithium ion battery as claimed in claim 2, wherein the centrifugation in the step (2) is performed at a rotation speed of 7000-8000 rpm for 4-6 times, and the drying is performed at a temperature of 55-65 ℃ for 5-8 hours.

10. The method for preparing the MIL-125(Ti) -based lithium titanate negative electrode material of the lithium ion battery as claimed in claim 2, wherein the calcination temperature of the lithium titanate precursor material in the step (3) is 650-750 ℃, and the calcination time is 6-10 hours.

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