WO2017008624A1 - Method for fabricating lithium titanate silicon-based composite negative-electrode material - Google Patents

Abstract

Provided is a method for fabricating a lithium titanate silicon-based composite negative-electrode material; in the method, a resinous carbon precursor is used to coat nano-silicon; the resinous precursor is carbonized to form a porous structure carbon, which is used as a carrier on which to secure nano-silicon, effectively mitigating the volume expansion of the silicon; then, after compositing with lithium titanate, bitumen coating modification is performed, thus resolving the shortcomings of the specific surface area of the resinous material being excessively large and the capacity of the lithium titanate being low; a large and irreversible loss of capacity is prevented, improving the gram specific capacity of the material; the material ultimately obtained has the advantages of a low specific surface area, good processability, and high gram specific capacity and a long cycle. At the same time, the method is simple to perform, easy to control, has low production costs, and is suitable for industrial production.

Description

Method for preparing lithium titanate silicon-based composite anode material Technical field

The invention relates to the field of anode materials for lithium ion batteries, and in particular to a method for preparing lithium titanate silicon composite anode materials for lithium ion batteries.

Background technique

At present, with the shortage of global petroleum resources and the deteriorating climate environment, the development of human society faces severe challenges. The development of clean and energy-efficient new energy vehicles has been highly valued by countries around the world. The development of new energy vehicles is the key to their power supply. Lithium-ion batteries have the advantages of high energy density, small self-discharge, no memory effect, wide operating voltage range, long service life and no environmental pollution. They are the main power source for new energy vehicles. The key electrode material of lithium ion battery is the final determinant of battery performance, and the negative electrode material plays an important role in improving the performance of lithium ion battery. Therefore, the development of high-performance, low-cost anode materials is of great significance to promote the development of new energy vehicles and related emerging industries.

The current anode material is mainly graphite, and its specific capacity is close to the theoretical value of 372 mAh/g. It is difficult to have room for improvement. Therefore, finding a high specific capacity anode material instead of carbon has become an important development direction. As a new type of lithium ion secondary battery anode material, Li4Ti5O12 has the advantages of good cycle performance, no reaction with electrolyte, high safety performance, stable charge and discharge platform, etc., compared with other commercial materials. One of the most excellent anode materials for lithium-ion batteries that are of interest. Compared with carbon negative electrode materials, lithium titanate has many advantages. Among them, the deintercalation of lithium ions in lithium titanate is reversible, and the crystal form of lithium ion in the process of inserting or extracting lithium titanate is not Changed, volume change is less than 1%, so it is called "zero strain material", which can avoid the structure damage caused by the back and forth expansion of the electrode material in the charge and discharge cycle, thereby improving the cycle performance and service life of the electrode, reducing the The number of cycles increases and the specific capacity is greatly attenuated, which has better cycle performance than the carbon negative electrode; however, since lithium titanate is an insulating material, its electrical conductivity is low, resulting in the rate performance in the application of lithium battery. The problem is poor. At the same time, the theoretical specific capacity of lithium titanate material is 175mAh/g, the actual specific capacity is more than 160mAh/g, and it has the disadvantages of low gram capacity. Therefore, it is necessary to modify lithium titanate.

The silicon-based anode has unique advantages and potential. The silicon anode material can form Li ₁₂ Si ₇ , Li ₁₃ Si ₄ , Li ₇ Si ₃ , Li ₁₅ Si ₄ , Li ₂₂ Si ₅ and other alloys with lithium during charge and discharge. It has the advantages of high capacity (Li ₂₂ Si ₅ , up to 4200 mAh/g), low voltage for deintercalating lithium, low reactivity with electrolyte, and good safety performance. However, during the deintercalation of lithium, silicon undergoes a violent volume expansion (0 to 300%), which causes destruction and pulverization of the material structure, resulting in rapid decay of capacity and deterioration of cycle performance. In addition, silicon negative electrodes also have defects such as low conductivity, poor rate performance, and low coulombic efficiency.

Studies have shown that the composite material obtained by the combination of metal powder with silicon powder and lithium titanate can greatly improve the performance of lithium titanate anode material. The metal itself has good ductility, high electrical conductivity and high mechanical strength. Therefore, selecting suitable metal and silicon to form silicon carbon can effectively overcome the volume effect of silicon during charge and discharge, improve the cycle stability of the material, and conduct electricity. Sex has also improved. However, the capacity and the first effect of the existing silicon carbon negative electrode materials are generally low, and the prepared materials have poor consistency.

Therefore, the development of a lithium titanate composite anode material with high conductivity, high capacity, high first charge and discharge efficiency and good cycle stability is a technical problem in the field of lithium ion batteries.

Summary of the invention

In view of the problems existing in the prior art, one of the objects of the present invention is to provide a method for preparing a lithium titanate silicon-based composite anode material, which first coats nano-silicon with a resin-based carbon precursor, and the carbon precursor passes through The porous structure is formed after high temperature carbonization, which can effectively alleviate the volume expansion effect of silicon, and then coat The carbonized material is pulverized to obtain a submicron powder, and then mixed with lithium titanate or a pitch-based carbon precursor, and then subjected to high-temperature treatment to be cooled and sieved to obtain a lithium titanate-based composite negative electrode material of the present invention.

A preparation method of lithium titanate silicon-based composite anode material, the specific preparation steps are as follows:

(1) dispersing the resin-based carbon precursor in a solvent, adding nano-silicon, then ultrasonically dispersing, evaporating the organic solvent, and under high-temperature carbonization, obtaining a material A;

(2) The material A is pulverized to obtain a submicron powder B having a particle diameter D50 of 0.1 to 1 μm;

(3) The powder B is solid-phase mixed with the lithium titanate and the pitch-based carbon precursor, and then carbonized at a high temperature under the protection of an inert gas, and cooled and sieved.

Further, the resin-based carbon precursor in the step (1) means one of a furfural resin, an epoxy resin, a phenol resin, a polyethylene glycol, a polyvinyl chloride, a polyvinyl butyral, a polyacrylonitrile, and a polyacrylic acid. Or a combination of at least two.

Further, the ratio of the resin-based carbon precursor to the nano-silicon in the step (1) is 1: (0.05 to 0.15).

Further, the temperature of the high-temperature carbonization in the step (1) is 650 to 850 ° C, the heating rate is 1 to 5 ° C / min, and the holding time is 0.5 to 3 h.

Further, the step (2) pulverization refers to one or a combination of two or more of ball milling, mechanical pulverization, or air pulverization.

Further, the weight ratio of the powder B to the lithium titanate in the step (3) is (0.1 to 0.5): 1, and the pitch-based carbon precursor accounts for 10 to 30% of the total weight of the powder B and the lithium titanate.

Further, the asphalt-based carbon precursor in the step (3) refers to a combination of one or at least two of a condensed polycyclic polynuclear hydrocarbon obtained by upgrading coal tar pitch, petroleum pitch, modified pitch, mesophase pitch, and pitch. .

Further, the powder particle diameter D50 of the pitch-based carbon precursor in the step (3) is ≤ 3 μm.

Further, the temperature of the high temperature carbonization in the step (3) is 850 to 1000 ° C, the heating rate is 5 to 20 ° C / min, and the holding time is 0.5 to 4 h.

The porous structure carbon formed by carbonization of the resin-based carbon precursor serves as a carrier for fixing the nano-silicon, and utilizes the characteristics of many small organic molecules in the resin. At high temperatures, small molecules overflow from the surface to form micropores, and the nano-silicon is uniformly embedded in the micro-pores. The method can improve the dispersibility of the nano silicon particles in the silicon-based composite anode material, alleviate the volume expansion and contraction of the material during lithium removal/intercalation, enhance the structural stability of the material, and ensure the material has a high electrical conductivity. Improve the electrochemical properties of materials and their cycle stability.

After being compounded with lithium titanate, the asphalt coating modification treatment solves the disadvantages of excessive surface area of the resin material and low capacity of the lithium titanate, avoiding large irreversible capacity loss and increasing the ratio of the material. Capacity, the resulting material has a low specific surface area, good processing properties and high specific capacity and long cycle.

At the same time, the method of the invention is simple in operation, easy to control, low in production cost, and suitable for industrial production.

detailed description

In order to better understand the present invention, the technical solutions of the present invention will be specifically described below by way of specific embodiments.

Example 1

Disperse the epoxy resin in acetone solvent, add silicon powder according to the ratio of epoxy resin: nano silicon=1:0.1, then ultrasonically disperse, evaporate the organic solvent, and under the protection of inert gas, the heating rate is 2 °C/min. It is raised to 750 ° C, kept for 2 h, and the powder obtained by carbonization is pulverized by jet milling to a D50 of 0.1 to 1 μm, and then the powder and lithium titanate are 0.3:1 by weight, while adding powder and titanic acid. Total weight of lithium 15% petroleum asphalt (D50=2.15μm) was mixed together. After the components were uniformly mixed, the powder was raised to 850 °C at a heating rate of 10 °C/min under inert gas protection, kept for 3 hours, and cooled to room temperature. Thereafter, the lithium titanate silicon-based composite negative electrode material prepared by the present invention is obtained by sieving.

Example 2

Dispersing the phenolic resin in an alcohol solvent, adding the silicon powder according to the ratio of phenolic resin: nano silicon=1:0.15, then ultrasonically dispersing, evaporating the organic solvent, and raising to a temperature increase rate of 3 ° C/min under the protection of an inert gas. 800 ° C, holding for 3 h, using a ball mill pulverization, the powder obtained after carbonization is pulverized to a D50 of 0.1 to 1 μm, and then the powder and lithium titanate are 0.4:1 by weight, while adding powder and lithium titanate total 20% of the coal tar pitch (D50=2.15μm) is mixed together. After the components are uniformly mixed, the powder is raised to 1000 ° C at a heating rate of 10 ° C / min under the protection of an inert gas, and the temperature is kept for 0.5 h. After cooling to room temperature, the lithium titanate silicon-based composite anode material prepared by the present invention is obtained by sieving.

Example 3

Disperse polyethylene glycol in deionized, add silicon powder according to the ratio of polyethylene glycol: nano silicon = 1:0.05, then ultrasonically disperse, evaporate the organic solvent, under the protection of inert gas, at 5 ° C / min The heating rate is raised to 850 ° C, and the temperature is kept for 1 h. The powder obtained by carbonization is pulverized by mechanical pulverization to a D50 of 0.1 to 1 μm, and then the powder and the lithium titanate are 0.5:1 by weight, and the powder is added simultaneously. 30% of the total weight of lithium titanate is mixed with mesophase pitch (D50=2.15μm). After the components are uniformly mixed, the powder is raised to 900 °C at a heating rate of 15 °C/min under inert gas protection. After heat preservation for 1.5 hours, after cooling to room temperature, the lithium titanate silicon-based composite anode material prepared by the invention is obtained by sieving.

Example 4

Dispersing the phenolic resin in an alcohol solvent, adding the silicon powder according to the ratio of resin: nano silicon=1:0.1, then dispersing ultrasonically, evaporating the organic solvent, and raising to 850 at a heating rate of 2 ° C/min under the protection of an inert gas. °C, heat preservation for 0.5h, the powder obtained by carbonization is pulverized by jet milling to a D50 of 0.1 to 1 μm, and then the powder and lithium titanate are 0.25:1 by weight, while adding powder and lithium titanate total 20% of the modified asphalt (D50=2.15μm) was mixed together. After the components were uniformly mixed, the powder was raised to 850 °C at a heating rate of 5 °C/min under an inert gas atmosphere for 2.5 h. After cooling to room temperature, the lithium titanate silicon-based composite anode material prepared by the present invention is obtained by sieving.

Comparative example 1

The one-component lithium titanate of Example 1.

Comparative example 2

According to the preparation procedure in Example 1, the difference was in the negative electrode material finally obtained without adding silicon powder.

Half battery test

To test the electrical properties of the negative electrode material prepared by the method of the present invention, the test was carried out by a half-cell test method using the negative electrode materials of the above examples and comparative examples: acetylene black: PVDF (polyvinylidene fluoride) = 93:3:4 (weight Ratio, adding appropriate amount of NMP (N-methylpyrrolidone) into a slurry, coating on copper foil, drying at 110 ° C for 8 hours to make a negative electrode sheet; using lithium metal sheet as the counter electrode, the electrolyte is 1 mol / L LiPF6/EC+DEC+DMC=1:1:1, the polypropylene microporous membrane is a membrane and assembled into a battery. The charge-discharge voltage is 1.0-2.5V, and the charge-discharge rate is 0.5C. The battery performance can be tested. The test results are shown in Table 1.

Full battery test

Using the negative electrode materials of the above examples and comparative examples: SP: SBR (solid content: 50%): CMC = 94: 2.5: 1.5: 2 (weight ratio), adding appropriate amount of deionized water, mixing and evenly slurrying, applied to copper On the foil, vacuum drying at 90 ° C; LiCoO ₂ powder: SP: KS-6: PVDF = 94: 1.5: 2: 2.5 (weight ratio), uniformly mixed with NMP as a solvent, and then applied to aluminum foil On the top, vacuum drying at 100 ° C; the dried positive and negative pole pieces through rolling, cutting, winding, injecting, sealing, forming process, to make 18650 cylindrical battery, the diaphragm is Celgard 2400, the electrolyte is 1M LiPF6/DMC: EC: DEC, using a battery detection device for cycle performance detection, the test results are shown in Table 1.

Table 1 Comparison of properties of anode materials in different examples and comparative examples

The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and combinations thereof may be made without departing from the spirit and scope of the invention. Simplifications should all be equivalent replacements and are included in the scope of the present invention.

Claims (8)

1. A preparation method of lithium titanate silicon-based composite anode material, the specific preparation steps are as follows:

   (1) dispersing the resin-based carbon precursor in a solvent, adding nano-silicon, then ultrasonically dispersing, evaporating the organic solvent, and under high-temperature carbonization, obtaining a material A;

   (2) The material A is pulverized to obtain a submicron powder B having a particle diameter D50 of 0.1 to 1 μm;

   (3) The powder B is solid-phase mixed with the lithium titanate and the pitch-based carbon precursor, and then carbonized at a high temperature under the protection of an inert gas, and cooled and sieved.
2. The method for preparing a lithium titanate silicon-based composite anode material according to claim 1, wherein the resin-based carbon precursor in the step (1) is a furfural resin, an epoxy resin, a phenol resin, or a polyethylene glycol. A combination of one or at least two of polyvinyl chloride, polyvinyl butyral, polyacrylonitrile, and polyacrylic acid.
3. The method for preparing a lithium titanate silicon-based composite anode material according to claim 1, wherein the ratio of the resin-based carbon precursor to the nano-silicon in the step (1) is 1: (0.05 to 0.15).
4. The method for preparing a lithium titanate silicon-based composite anode material according to claim 1, wherein the temperature of the high temperature carbonization in the step (1) is 650 to 850 ° C, the heating rate is 1 to 5 ° C / min, and the heat preservation is performed. The time is 0.5 to 3 hours.
5. The method for preparing a lithium titanate silicon-based composite anode material according to claim 1, wherein the step (2) pulverization refers to one or a combination of two or more of ball milling, mechanical pulverization or air pulverization. .
6. The method for preparing a lithium titanate silicon-based composite anode material according to claim 1, wherein the weight ratio of the powder B to the lithium titanate in the step (3) is (0.1 to 0.5): 1, the asphaltic carbon The precursor accounts for 10 to 30% of the total weight of the powder B and the lithium titanate.
7. The method for preparing a lithium titanate silicon-based composite anode material according to claim 1, wherein the asphalt-based carbon precursor in the step (3) refers to coal pitch, petroleum pitch, modified asphalt, mesophase pitch, One or a combination of at least two of the condensed polycyclic polynuclear aromatic hydrocarbons obtained by upgrading the pitch, and the powder particle diameter D50 of the pitch-based carbon precursor is ≤ 3 μm.
8. The method for preparing a lithium titanate silicon-based composite anode material according to claim 1, wherein the temperature of the high temperature carbonization in the step (3) is 850 to 1000 ° C, the heating rate is 5 to 20 ° C / min, and the heat preservation The time is 0.5 to 4 hours.