CN106207089A - A kind of used as negative electrode of Li-ion battery lithium titanate nano-tube material and preparation method thereof - Google Patents

Abstract

The invention discloses a lithium titanate nanotube material for a negative electrode of a lithium ion battery and a preparation method thereof, aiming at improving the charge transport characteristic of lithium titanate so as to exert its high rate charge and discharge performance. The raw material of the lithium titanate nanotube of the present invention is titanium salt: lithium salt Ti: Li=1:1~1.5, its molecular formula is Li ₄ Ti ₅ O ₁₂ , and the diameter of the lithium titanate nanotube is 1- 20nm with a length of 50‑50nm. The method is a dynamic stirring driving force method, by controlling the ratio of precursor titanium salt/lithium salt, solvothermal temperature/time, supplemented by subsequent procedures such as centrifugation/washing/drying/calcination, etc., to obtain lithium titanate nanotube materials . It has been determined that when the lithium titanate nanotube material prepared by the present invention is used as the negative electrode material of the lithium ion battery, it has high mass specific capacity and cycle stability. At the same time, the preparation method of the invention has the advantages of low reaction temperature, controllable reaction, etc., is suitable for large-scale production, and has very broad development prospects.

Description

Lithium titanate nanotube material for negative electrode of lithium ion battery and preparation method thereof

technical field

The invention relates to the field of materials, in particular to the technical field of lithium-ion battery negative electrodes, and specifically relates to a lithium titanate nanotube material for lithium-ion battery negative electrodes and a preparation method thereof. The lithium titanate nanotube material of the present invention is expected to improve the reversible specific capacity of lithium ion batteries, which is of great significance to the development of lithium ion batteries.

Background technique

Lithium-ion batteries have the advantages of high voltage, high energy density, light weight, small internal resistance, long cycle life, no memory effect, and environmental friendliness. Fields such as fuel vehicles and national defense technology have huge market potential.

Lithium-ion batteries are mainly composed of four parts: positive electrode, negative electrode, electrolyte and separator. It is essentially a lithium-ion concentration battery, with positive and negative electrodes composed of different lithium-ion intercalation compounds. As a key material in lithium-ion batteries, the performance of negative electrode materials will directly affect the overall performance of the battery. Carbon materials are the earliest and most widely used lithium-ion battery negative plate materials. Carbon materials have low lithium ion insertion potential, high specific capacity, good electrical conductivity, good cycle performance, are not easy to react with organic solvents, and are rich in resources, low in price, non-toxic and non-polluting. Japan's Sanyo Corporation uses high-quality natural graphite to interact with an appropriate amount of water vapor at high temperatures to improve its ability to intercalate lithium. Studies by Sony and Nissan have shown that defects on the surface and edges of graphene can accommodate a large amount of lithium ions, increasing the specific capacity. However, there is limited space for improving the mass-to-capacity ratio of carbon materials, and it is easy to form lithium dendrites when charged at high rates and low temperatures, causing short-circuit safety hazards and limiting its popularization and application.

It is possible to significantly improve the electrochemical performance of anode materials by nanosizing the anode materials. First of all, nanomaterials can effectively reduce the time of lithium ion intercalation and deintercalation, and enhance the rapid charge and discharge performance of materials; secondly, more grain boundaries can provide fast lithium ion transport channels and increase the charge exchange rate; thirdly, nanomaterials exist Larger voids can accommodate expansion, while smaller absolute volume changes can reduce structural instability caused by volume changes during cycling, and larger deformability can withstand the stress caused by volume changes, so it can effectively improve the cycle of materials performance.

In particular, the one-dimensional nanoarray can effectively improve the cycle performance and high-rate charge-discharge performance of the negative electrode by virtue of its unique directional structure. This is due to: (1) the large specific surface area of the one-dimensional nanoarray increases the surface defects and active sites, which can improve the specific capacity of the material; (2) the electrolyte can enter the interior of the one-dimensional nanoarray, which improves the The contact between the active material and the electrolyte increases the diffusion rate of lithium ions and improves the high-rate charge-discharge performance of the material; (3) the intercalation and deintercalation distance of lithium ions is short, and the one-dimensional nano-array structure enhances electronic conduction (4) The gap in the middle of the one-dimensional nano-array can accommodate the expansion of the material during the charge-discharge process, reducing the cracking and pulverization of the material, and the structure of the one-dimensional nano-array can be Prevent the agglomeration of materials, thus effectively improving the cycle stability.

Among them, lithium titanate has attracted extensive attention due to its excellent high-rate charge-discharge performance. Lithium titanate belongs to the spinel structure, and its structure can provide a three-dimensional channel for the diffusion of lithium ions. During the intercalation and extraction of lithium ions, the unit cell parameters of lithium titanate change very little, and the volume change of the unit cell is only 0~0.3%, so lithium titanate is usually called "zero strain" material.

The extremely low volume change and sufficient lithium ion channels make lithium titanate have excellent cycle performance and high rate charge and discharge performance. However, the theoretical specific capacity of the lithium titanate electrode is only 175.1 mAh/g, which is less than half of that of commercial graphite. At the same time, the potential of lithium ion intercalation is high (1.55 V vs Li/Li ⁺ ), making the open circuit voltage of the entire lithium ion battery Low, which limits the application of lithium titanate as a negative electrode material.

Contents of the invention

The purpose of the present invention is to provide a lithium titanate nanotube material for the negative electrode of a lithium ion battery and a preparation method thereof in view of the above existing problems. Different from the existing lithium titanate particles, the present invention proposes a lithium titanate nanotube for the negative electrode of the lithium ion battery, which has a higher mass specific capacity and plays an important role in the development of the lithium ion battery. At the same time, the present invention provides a method for preparing lithium titanate nanotubes for negative poles of ultra-lithium ion batteries. The method uses titanium salt and lithium salt as raw materials respectively, adopts a dynamic stirring driving force method, and controls the precursor titanium salt/lithium salt The ratio, solvothermal temperature/time, supplemented by subsequent procedures such as centrifugation/washing/drying/calcination, the lithium titanate nanotube material is obtained. It has been determined that when the lithium titanate nanotube material prepared by the present invention is used as the negative electrode material of the lithium ion battery, it has high mass specific capacity and cycle stability. At the same time, the preparation method of the invention has the advantages of low reaction temperature, controllable reaction, etc., is suitable for large-scale production, and has very broad development prospects.

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

A lithium titanate nanotube material for a negative electrode of a lithium ion battery, wherein the raw material of the lithium titanate nanotube is titanium salt: lithium salt Ti: Li=1:1~1.5, and its molecular formula is Li ₄ Ti ₅ O ₁₂ , The diameter of the lithium titanate nanotube is 1-20nm, and the length is 50-50nm.

A method for preparing a lithium titanate nanotube material for a negative electrode of a lithium ion battery, comprising the following steps: using titanium salt and lithium salt as raw materials, and adopting a dynamic stirring driving force method to prepare the product; wherein, the solvothermal temperature is 90 ^o C ~200 ^o C, solvent heat time is 8h~80h.

Specific steps include:

(1) Weigh titanium salt and lithium salt respectively according to the stoichiometric ratio of Ti:Li=1:(1~1.5);

(2) After mixing the titanium salt and lithium salt weighed in step 1, add them to the solvent, stir them well, and mix them evenly to obtain the first mixture;

(3) Put the first mixture obtained in step 2 in a high-temperature hydrothermal kettle, place the reaction kettle in an oil bath and heat it with magnetic stirring at a speed of 100-500rpm, and heat at 90 ^o C ~ 200 ^o C for 8h ~ 80h, get the first product;

(4) Centrifuging, washing and drying the primary product obtained in step 3 with deionized water and hydrochloric acid in sequence to obtain the secondary product;

(5) Put the secondary product obtained in step 4 into (0.1-1) M lithium hydroxide solution, perform ion exchange, magnetically stir for 10 minutes, and sonicate for 1 hour;

(6) Put the product obtained in step 5 into a muffle furnace and heat-treat at 500 ^o C for 6 hours to obtain the final product.

Further, the titanium salt is one or more of P25, tetraethyl titanate, tetrabutyl titanate, titanium isopropoxide, and titanium trichloride.

Further, the lithium salt is one or more of lithium hydroxide, lithium nitrate, lithium sulfate, and lithium perchlorate.

Further, in the step 2, the solvent is one or more of water, ethanol, isopropanol, tert-butanol, and N,N-dimethylformamide.

Further, in step 3, the first mixture obtained in step 2 is placed in a high-temperature hydrothermal kettle, heated by water bath, oil bath, microwave or ultrasonic at 90 ^o C ~ 200 ^o C for 8h ~ 80h .

Further, in the step 6, vacuum drying or nitrogen protective atmosphere drying is adopted, the drying time is 1-15 hours, and the drying temperature is 400 o ^C ~ 700 ^o C.

In view of the foregoing problems, the present invention provides a lithium titanate nanotube material for negative electrodes of lithium ion batteries and a preparation method thereof. In the present invention, the principle of the high specific capacity of the lithium titanate nanotube material is that the one-dimensional nanoarray structure of the lithium titanate nanotube enhances the electronic conductivity, improves the high-rate charge and discharge performance of the material, and fully utilizes its high-rate Charge and discharge performance and good cycle performance.

detailed description

All features disclosed in this specification, or steps in all methods or processes disclosed, may be combined in any manner, except for mutually exclusive features and/or steps.

Any feature disclosed in this specification, unless specifically stated, can be replaced by other alternative features that are equivalent or have similar purposes. That is, unless expressly stated otherwise, each feature is one example only of a series of equivalent or similar features.

Example 1

To synthesize about 0.4 g of high-purity spinel-type lithium titanate Li ₄ Ti ₅ O ₁₂ , it is necessary to weigh the precursor P25 and lithium hydroxide respectively, and control the stoichiometric ratio Ti:Li=1:1.25. The weighed precursor was placed in a hydrothermal reaction kettle, and 25 mL of deionized water was added into the hydrothermal reaction kettle, and stirred for 30 min to mix the components uniformly to obtain the first mixture. Then the hydrothermal reaction kettle was placed in an oil bath and heated with magnetic stirring at 120 ^o C for 24 hours at a rotation speed of 300 rpm to obtain the initial product. The primary product was centrifuged, washed, and dried with deionized water and hydrochloric acid in sequence to obtain the secondary product; then the secondary product was placed in a 0.2 M lithium hydroxide solution for ion exchange, magnetically stirred for 10 minutes, and ultrasonically treated for 1 hour; Finally, it was put into a muffle furnace and heat-treated at 500 ^o C for 2 hours to obtain the final product.

The preparation method of lithium-ion battery: mix the active material lithium titanate nanotube material, acetylene black conductive agent, and binder (PVDF) in a mass ratio of 80:10:10, and drop an appropriate amount of N-methylpyrrolidone to make a uniform of black paste. Apply it evenly on the aluminum foil current collector with a spatula, and dry it in vacuum at 120°C for 12 hours to obtain a lithium titanate electrode sheet. In a glove box with an argon atmosphere, lithium foil was used as the negative electrode, lithium titanate electrode was used as the positive electrode, polypropylene porous membrane was used as the diaphragm, and a mixed solution of 1M LiPF6 was used as the electrolyte to assemble a button battery.

Test results: The lithium titanate nanotube-based lithium-ion battery negative electrode prepared in this example has a specific discharge capacity of 107 mAh/g for the first time under the high-rate charge and discharge of 3C; after 100 cycles, the capacity retention is still 70mAh/g. g; Coulombic efficiency is about 100%.

The properties of the lithium titanate nanotube-based lithium-ion battery negative electrode obtained by changing the composition of the synthetic precursor of Li ₄ Ti ₅ O ₁₂ and keeping other conditions unchanged are shown in Table 1 below.

Table 1 Determination results under different raw materials and mass ratio conditions

It can be seen from Table 1 that changing the titanium source and lithium source will directly affect the specific capacity and Coulombic efficiency of Li ₄ Ti ₅ O ₁₂ . This is due to the different solubility and ease of ion dissociation of different precursors, which in turn affects the reaction rate of the precursors in the hydrothermal reaction. At the same time, an appropriate ratio of titanium to lithium can also ensure the formation of a stable spinel structure product, and use its three-dimensional ion diffusion channel to ensure the mass specific capacity of the system.

Example 2

According to the steps described in Example 1, P25 and lithium hydroxide are used as titanium source and lithium source, and the stoichiometric ratio of the stoichiometric elements is kept at 1:1.25. The solvent type, solvothermal temperature and solvothermal time are changed respectively. Under the premise of changing, the performance of the obtained lithium titanate nanotube-based lithium ion battery negative electrode is shown in Table 2 below.

Table 2 Determination results under different solvents, pH value, solvothermal temperature and solvothermal time

Example 3

According to the steps and components described in Example 1, the drying atmosphere, temperature and time of the hydrothermal product were changed respectively, and under the premise that other conditions remained unchanged, the performance of the negative electrode of the obtained lithium titanate nanotube-based lithium ion battery was tested. , the test results are shown in Table 3 below.

Table 3 Determination results under different drying conditions

The above is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed in the present invention can easily think of changes or Replacement should be covered within the protection scope of the present invention. The present invention extends to any new feature or any new combination disclosed in this specification, and any new method or process step or any new combination disclosed.

Claims (7)

1. Lithium titanate nanotube material for lithium ion battery negative electrode, it is characterized in that: the raw material of described lithium titanate nanotube is titanium salt: lithium salt Ti: Li=1: 1～1.5, and its molecular formula is Li ₄ Ti ₅ O ₁₂ , the diameter of the lithium titanate nanotube is 1-20nm, and the length is 50-50nm. 2. a preparation method of lithium titanate nanotube material for lithium ion battery negative pole as claimed in claim 1, it is characterized in that described method comprises the steps: (1) Weigh titanium salt and lithium salt respectively according to the stoichiometric ratio of Ti:Li=1:(1~1.5); (2) After mixing the titanium salt and lithium salt weighed in step 1, add them to the solvent, stir them well, and mix them evenly to obtain the first mixture; (3) Put the first mixture obtained in step 2 in a high-temperature hydrothermal kettle, place the reaction kettle in an oil bath and heat it with magnetic stirring at a speed of 100-500rpm, and heat at 90 ^o C ~ 200 ^o C for 8h ~ 80h, get the first product; (4) Centrifuging, washing and drying the primary product obtained in step 3 with deionized water and hydrochloric acid in sequence to obtain the secondary product; (5) Put the secondary product obtained in step 4 into (0.1-1) M lithium hydroxide solution, perform ion exchange, magnetically stir for 10 minutes, and sonicate for 1 hour; (6) Put the product obtained in step 5 into a muffle furnace and heat-treat at 500 ^o C for 6 hours to obtain the final product lithium titanate nanotube material for the negative electrode of lithium-ion batteries. 3. the preparation method of lithium titanate nanotube material for negative electrode of lithium ion battery according to claim 2, is characterized in that, described titanium salt is P25, tetraethyl titanate, tetrabutyl titanate, Virahol One or more of titanium and titanium trichloride. 4. the preparation method of lithium titanate nanotube for negative electrode of lithium ion battery according to claim 2, is characterized in that, described lithium salt is the one in lithium hydroxide, lithium nitrate, lithium sulfate, lithium perchlorate or more. 5. the preparation method of lithium titanate nanotube material for negative electrode of lithium ion battery according to claim 2, is characterized in that, in described step 2, solvent is water, ethanol, Virahol, tert-butyl alcohol, N, One or more of N-dimethylformamide. 6. the preparation method of lithium titanate nanotube material for negative electrode of lithium ion battery according to claim 2, is characterized in that, in described step 3, the first mixture that step 2 obtains is placed in high-temperature hydrothermal kettle, Use water bath, oil bath, microwave or ultrasonic heating, and heat at 90 ^o C ~ 200 ^o C for 8h ~ 80h; in the step 3, place the first mixture obtained in step 2 in a high-temperature hydrothermal kettle, and use a water bath , oil bath, microwave or ultrasonic heating, at 90 ^o C ~ 200 ^o C, heating for 8h ~ 80h. 7. the preparation method of lithium titanate nanotube material for negative electrode of lithium ion battery according to claim 2, is characterized in that, in described step 6, adopts vacuum drying or nitrogen protective atmosphere to dry, and drying time is 1～15h, The drying temperature is 400 ^oC ~700^oc.