CN112803005B

CN112803005B - Preparation method and application of silicon-carbon negative electrode material of lithium ion battery

Info

Publication number: CN112803005B
Application number: CN202110239780.5A
Authority: CN
Inventors: 董骄; 曹勇; 王义飞; 苏峰; 马仁良; 项胜; 鲁冰冰
Original assignee: Hefei Guoxuan High Tech Power Energy Co Ltd
Current assignee: Hefei Gotion High Tech Power Energy Co Ltd
Priority date: 2021-03-04
Filing date: 2021-03-04
Publication date: 2022-05-13
Anticipated expiration: 2041-03-04
Also published as: CN112803005A

Abstract

The invention discloses a modification method of a silicon film cathode material of a lithium ion battery, which comprises the following steps: (1) dispersing raw materials; (2) pretreatment of the spraying liquid; (3) electrostatic spraying; (4) high-temperature pyrolysis; (5) and (4) cutting and hot-pressing the silicon-carbon negative electrode material obtained in the step (4). The invention also provides the application of the lithium ion battery silicon-carbon negative electrode material prepared by the preparation method in the preparation of the lithium ion battery. According to the invention, silicon particles are directly dispersed in an organic system, the carbon-coated lithium ion battery silicon-carbon cathode material is obtained by an electrostatic spinning technology and pyrolysis mode, the carbon coating amount and the coating form are regulated and controlled by adjusting the composition, solid content, viscosity and dielectric constant of the silicon-organic dispersion system and matching with parameters such as a needle head, voltage and distance of electrostatic spraying, the coating effect is obvious, the coating efficiency is high, the coating process is simple, and the cost can be effectively saved in mass production.

Description

Preparation method and application of silicon-carbon negative electrode material of lithium ion battery

Technical Field

The invention relates to the technical field of lithium ion battery materials, in particular to a preparation method and application of a silicon-carbon cathode material of a lithium ion battery.

Background

Under the new situation that the state vigorously advances the new energy industry, the lithium ion battery is distinguished by the excellent properties of high energy density, long service life, high rated voltage of a single battery core and the like, and becomes the main energy form for developing the new energy industry at present. Commercial lithium ion batteries mostly adopt carbonaceous negative pole matching lithium iron phosphate or ternary positive pole materials, and along with the increasing market demand for high-energy-density lithium ion batteries and the promotion of national subsidy policy threshold, the problems of low energy density, high production cost and the like of the lithium ion batteries are urgently needed to be solved.

The breakthrough of the development of the high-energy density lithium ion battery can be started from positive and negative electrode materials, the positive electrode material is represented by high-nickel ternary, and the silicon-based negative electrode material is the development trend. Silicon is the lithium ion battery anode material with the highest known specific capacity (4200mAh/g), but finally causes the deterioration of electrochemical performance due to the huge volume effect (> 300%). The volume expansion rate of the silicon oxide in the lithium intercalation and deintercalation process is small (for example, SiO is only 150%), and the silicon oxide also has higher theoretical specific capacity (more than 1200 mAh/g), but Li in the lithium intercalation and deintercalation process for the first time₂The O and lithium silicate formation processes are irreversible, while Li₂O and lithium silicates have poor conductivity, resulting in poor electrochemical kinetics and thus poor rate performance, and their stability remains poor as cycling times continue to increase. In addition, although nano-sized silicon particles have better electrochemical properties than micro-sized silicon particles, when the size is reduced below 100nm, the silicon active particles are easily agglomerated during charge and discharge, thereby accelerating capacity fade.

Aiming at the problems of volume expansion of a silicon-based material, and reduction of conductivity, cycle performance, rate performance and the like caused by the volume expansion, the problems are mainly solved by compounding and coating a carbonaceous material (graphite, mesophase microspheres, carbon black, amorphous carbon, carbon nanotubes and the like). The carbonaceous negative electrode material has small volume change in the charge and discharge process, good circulation stability and good self-conductivity. In addition, silicon and carbon have similar chemical properties and can be tightly bonded, so carbon is often used as the preferred material for compounding with silicon. In a silicon-carbon composite system, a silicon-based material is used as an active substance to provide lithium storage content, and a carbonaceous material can buffer the volume change of a silicon cathode in the charging and discharging process, improve the conductivity of the silicon-based material, avoid the agglomeration of small particles in the circulating process and ensure that the obtained silicon-carbon cathode shows high specific capacity and long cycle life.

Patent CN111952558A discloses a preparation method of a silicon-carbon negative electrode material of a lithium ion battery; patent CN109285994A discloses a preparation method of a silicon-carbon negative electrode material of a lithium ion battery. Some of the mainstream methods for preparing silicon-carbon composite materials at present comprise: 1) the high-energy ball milling method is combined with the chemical vapor deposition method to directly deposit and grow silicon on the surface of the carbon fiber carbon tube, and the method has more complicated steps and difficult mass production; 2) the silica-carbon gel composite material is prepared by a sol/gel method, and the specific surface area of carbon gel is large, so that the first irreversible capacity of the silica-carbon gel composite material is large; 3) multi-step wet preparation, designing various initiators and dispersants, and various mixing, drying and heat treatment steps. The preparation methods have high preparation cost, or cannot accurately control the silicon-carbon ratio and the agglomeration of nano-scale silicon particles, and cannot meet the requirements of the existing market on the high-energy-density lithium ion battery.

The electrospinning method is a simple and effective method for preparing the one-dimensional nanostructure, and compared with other methods such as solid-phase reaction, sol-gel and hydrothermal method, the electrospinning method can obtain a uniform compound of the active material and carbon more easily. The electrostatic spinning technology combines the advantages of electric spraying and traditional solution dry spinning fibers, the fiber diameter is controllable, and the range can cover hundreds of nanometers to tens of micrometers. The electrospinning process does not require the use of chemical coagulation or high temperatures to produce the spin from solution, which makes the process particularly suitable for the production of large and complex particulate fibers. The electrostatic spinning method can utilize various materials to prepare the nano-fiber, and is a universal method with low cost and simple process.

Disclosure of Invention

The invention aims to overcome the defects and shortcomings of the first coulombic efficiency, the conductivity, the rate capability and the cycle performance of the silicon-based material caused by volume expansion and lower conductivity in the charging and discharging processes.

The invention solves the technical problems through the following technical means:

a preparation method of a silicon-carbon negative electrode material of a lithium ion battery comprises the following steps:

(1) dispersing raw materials: dispersing silicon particles in an organic system, stirring at a high speed to disperse the silicon particles to form stable slurry, and controlling the solid content of the slurry to be 20-50%;

(2) pretreatment of the spraying liquid: adding organic matters into the slurry obtained in the step (1) while dispersing at a high speed to adjust the viscosity to 1000cP, and adding organic salts to adjust the dielectric constant of a dispersion system to 10 to obtain a mixture;

(3) electrostatic spraying: spraying the mixture onto a collecting device by using a spraying head under the high voltage of 10-50kV to prepare a silicon-carbon material precursor, controlling the temperature of a spraying environment to be 25 +/-5 ℃ and the humidity to be 40-60%, controlling the spraying speed to be 1-100 mu L/s, controlling the spraying angle to be 0-90 degrees from the normal angle of a receiving surface, and controlling the distance between a needle head and the receiving surface to be 5-10 cm;

(4) high-temperature pyrolysis: carrying out high-temperature pyrolysis on the silicon-carbon material precursor obtained in the step (3) under the protection of inert gas, and cooling along with a furnace to obtain a carbon-coated silicon-carbon negative electrode material of the lithium ion battery;

(5) and (4) cutting and hot-pressing the silicon-carbon negative electrode material obtained in the step (4).

According to the invention, silicon particles are directly dispersed in an organic system, the carbon-coated lithium ion battery silicon-carbon cathode material is obtained by an electrostatic spinning technology and pyrolysis mode, the carbon coating amount and the coating form are regulated and controlled by adjusting the composition, solid content, viscosity and dielectric constant of the silicon-organic dispersion system and matching with parameters such as a needle head, voltage and distance of electrostatic spraying, the coating effect is obvious, the coating efficiency is high, the coating process is simple, and the cost can be effectively saved in mass production.

Preferably, the silicon particles in step (1) comprise micron-sized silicon, nano-sized silicon or silica.

Preferably, the organic system in step (1) is a mixture of a polymer and an organic solvent; the polymer comprises one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyvinylpyrrolidone, polyvinyl alcohol, polyacrylic acid, polybutylacrylate and polyacrylonitrile; the organic solvent comprises one or more of isopropanol, acetone and chloroform.

Preferably, the speed of high-speed stirring in the step (1) is 3000 rpm.

Preferably, the organic substance in the step (2) is a mixture of ethanol and starch.

Preferably, the organic salt in step (2) is sodium acetate.

Preferably, the spraying device in the step (3) comprises a flat plate type, a roller type, a spacing collection type and a combination of the devices or other auxiliary devices.

Preferably, the spraying head in the step (3) comprises a single needle, a coaxial needle, a side-by-side needle or a multi-needle.

Preferably, the pyrolysis temperature in the step (4) is 200-.

Preferably, the inert gas is argon.

Preferably, the hot-pressing temperature in the step (5) is 45-85 ℃, the hot-pressing time is 5-10min, and the hot-pressing pressure is 800-.

Preferably, the silicon-carbon negative electrode material obtained in the step (5) and a current collector are pressed to prepare a negative electrode piece.

Preferably, a conductive bonding layer is sprayed on the surface of the current collector, and the thickness of the sprayed layer is 10-50 mu m.

Preferably, the conductive adhesive layer is a mixture of a conductive agent and an adhesive; the conductive agent comprises one or more of a zero-dimensional nanoparticle conductive agent, a one-dimensional conductive agent and a two-dimensional conductive agent; the binder comprises PVDF, CMC and SBR mixture, polyacrylic acid, polyacrylonitrile or polyacrylate.

The nano-particle conductive agent comprises one or more of SP, acetylene black and Ketjen black; the one-dimensional conductive agent comprises one or two of carbon nano tubes and carbon fibers; the two-dimensional conductive agent is graphene.

An application of a lithium ion battery silicon carbon negative electrode material prepared by the preparation method of the lithium ion battery silicon carbon negative electrode material in the preparation of a lithium ion battery.

The invention has the following beneficial effects:

1. according to the invention, silicon particles are directly dispersed in an organic system, the carbon-coated lithium ion battery silicon-carbon cathode material is obtained by an electrostatic spinning technology and pyrolysis mode, the carbon coating amount and the coating form are regulated and controlled by adjusting the composition, solid content, viscosity and dielectric constant of the silicon-organic dispersion system and matching with parameters such as a needle head, voltage and distance of electrostatic spraying, the coating effect is obvious, the coating efficiency is high, the coating process is simple, and the cost can be effectively saved in mass production.

2. After the pyrolysis step is finished, residual high-temperature-resistant polymers uniformly dispersed among the carbon fibers exist in the organic system, the polymers can reasonably serve as binders for hot pressing of later-stage materials, and the silicon-carbon material has a good supporting effect on the overall structure of the silicon-carbon material.

3. The invention can prepare the negative plate with a certain shape in a specific application occasion, flexibly adjust the group domain, effectively utilize the battery assembly space and have obvious advantages in the application of the lithium ion battery of small and medium-sized equipment.

Drawings

Fig. 1 is a schematic structural diagram of a silicon-carbon negative electrode material prepared according to an embodiment of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings and the embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Test materials, reagents and the like used in the following examples are commercially available unless otherwise specified.

The specific techniques or conditions not specified in the examples can be performed according to the techniques or conditions described in the literature in the field or according to the product specification.

Example 1:

(1) dispersing crystalline nano-silicon with the D50 of 80nm in an organic system, wherein the organic system is a mixture of polyvinylidene fluoride, polytetrafluoroethylene and polyvinylpyrrolidone in a mass ratio of 1:2:1, stirring and dispersing at a high speed of 3000rpm to form stable slurry, and the solid content of the slurry is 20%;

(2) adding ethanol and starch into the slurry obtained in the step (1) while dispersing at a high speed to adjust the viscosity to 1000cP, and adding a proper amount of sodium acetate to adjust the dielectric constant of a dispersion system to 10 to obtain a mixture;

(3) under the voltage of 20kV, controlling the temperature and humidity of a spraying environment to be 25 +/-5 ℃ and 50% respectively, selecting a single needle for spraying, wherein the propelling speed of a spraying liquid is 1mL/h, the spraying direction is vertical to the plane of a collecting device, the distance is 10cm, the path is a snake-shaped reciprocating type, and spraying the mixture onto the collecting device to prepare a silicon-carbon material precursor;

(4) carrying out high-temperature pyrolysis on the obtained silicon-carbon material precursor at 300 ℃ under the protection of argon atmosphere, controlling the heating rate to be 5 ℃/min, controlling the pyrolysis time to be 5h, and carrying out furnace cooling under the protection of argon to obtain a carbon-coated silicon-carbon negative electrode material of the lithium ion battery;

(5) and (3) hot-pressing the obtained silicon-carbon negative electrode material for 5min at 60 ℃ and 1000kPa, cutting into proper circular sheets, using a lithium sheet as a reference electrode anode, and assembling a button half cell to test the electrical property of the button half cell.

As shown in figure 1, silicon particles 1 are directly dispersed in an organic system, a carbon-coated lithium ion battery silicon-carbon negative electrode material is obtained in a mode of electrostatic spinning and pyrolysis, after the pyrolysis step is finished, high-temperature-resistant polymers 3 uniformly dispersed among carbon fibers 2 are remained in the organic system, and the polymers 3 can reasonably serve as binders for hot pressing of later-stage materials and have a good supporting effect on the overall structure of the silicon-carbon negative electrode material.

Example 2:

the crystalline nano-silicon with the D50 of 50nm is adopted in the embodiment, and other preparation process parameters are kept consistent with those of the embodiment 1.

Example 3:

in this example, crystalline nano-silicon with a D50 of 100nm was used, and other preparation process parameters remained the same as in example 1.

Example 4:

the voltage in electrostatic spraying of this example was 10kV and other preparation process parameters remained the same as in example 1.

Example 5:

the voltage in electrostatic spraying of this example was 50kV and other preparation process parameters remained the same as in example 1.

Example 6:

the propelling speed of the spraying liquid in the electrostatic spraying of the embodiment is 0.5mL/h, and other preparation process parameters are kept consistent with those of the embodiment 1.

Example 7:

the propelling speed of the spraying liquid in the electrostatic spraying of the embodiment is 2mL/h, and other preparation process parameters are kept consistent with those of the embodiment 1.

Example 8

The preparation process of the carbon-coated lithium ion battery silicon-carbon negative electrode material is consistent with that of the embodiment 1, and the difference is that a conductive bonding layer is sprayed on the surface of a current collector, the spraying thickness is 20 micrometers, the conductive bonding layer is a mixture of a conductive agent and a binder, the conductive agent is SP, the binder is polyacrylonitrile, the mass ratio of the conductive bonding layer to the binder is 1:1, the conductive bonding layer and the binder are dispersed in isopropanol, and the solid content is 5%; and pressing the prepared carbon-coated silicon-carbon negative electrode material of the lithium ion battery and the treated current collector to prepare a negative plate, using the lithium plate as a reference electrode positive electrode, and assembling the negative plate and the prepared negative plate into a button half battery to test the electrical property of the button half battery.

Comparative example 1:

in the same way as in example 1, crystalline nano-silicon with D50 of 80nm is dispersed in an organic system and dried under the protection of inert gas at 60 ℃, high-temperature pyrolysis is carried out as described in example 1, and the electrical properties of the anode material are tested by the method of example 1.

Comparative example 2:

in the same way as in example 1, crystalline nanosilica with a D50 of 80nm was dispersed in an organic system and dried at 60 ℃ under an inert gas blanket, pyrolysed at high temperature as described in example 1, following the above materials: conductive agent SP: SBR: CMC 95: 3: 1:1, and preparing the anode material to be tested for electrical performance by means of deducting electricity according to the same loading capacity.

Table 1 shows the results of the electrical property tests of the batteries prepared in examples 1 to 7 and examples 1 to 2

As can be seen from table 1, the lithium ion battery silicon-carbon negative electrode materials provided in the embodiments of the present invention have high first coulombic efficiency and reversible capacity, which indicates that the carbon fiber constructed by the electrospinning method can effectively coat the nano-silicon, and avoid the side reaction caused by the direct contact between the carbon fiber and the electrolyte. Meanwhile, each embodiment has better rate performance and cycle performance, and the obtained silicon-carbon negative electrode material can effectively relieve performance attenuation caused by the volume effect of silicon in charge and discharge. In particular, it is noted that comparative example 1 failed 24 weeks of cycling because the direct press-fit assembly buckle test according to the preparation method of comparative example 1 resulted in more tiny interfaces within the material, greatly increased the frequency of side reactions, and further resulted in cell failure as the cell cycled. The invention effectively constructs a three-dimensional structure formed by the carbon fiber wrapped with the nano silicon and the polymer in the material as shown in figure 1, can effectively overcome structural damage caused by hot pressing, and avoids the generation of new interfaces.

In addition, it can be seen from examples 1-3 that effective carbon fiber coating can be formed by selecting nano-silicon with a proper particle size, and the nano-silicon is uniformly distributed in the carbon fiber to avoid contact with the electrolyte. From a comparison of examples 4-7 with example 1, it can be seen that different carbon fiber diameters can be obtained by adjusting parameters in electrospinning (this embodiment demonstrates the effect of both spray voltage and spray liquid advance rate parameters on cell performance), and optimal process parameters can be determined by further optimization experiments (not shown in this example).

The above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.

Claims

1. A preparation method of a silicon-carbon anode material of a lithium ion battery is characterized by comprising the following steps:

(1) dispersing raw materials: dispersing silicon particles in an organic system, stirring at a high speed to disperse the silicon particles to form stable slurry, and controlling the solid content of the slurry to be 20-50%; the organic system is a mixture of a polymer and an organic solvent; the polymer comprises one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyvinylpyrrolidone, polyvinyl alcohol, polyacrylic acid, polybutylacrylate and polyacrylonitrile; the organic solvent comprises one or more of isopropanol, acetone and chloroform;

(2) pretreatment of the spraying liquid: adding organic matters into the slurry obtained in the step (1) while dispersing at a high speed to adjust the viscosity to 1000cP, and adding organic salts to adjust the dielectric constant of a dispersion system to 10 to obtain a mixture; the organic matter is a mixture of ethanol and starch; the organic salt is sodium acetate;

(5) cutting and hot-pressing the silicon-carbon negative electrode material obtained in the step (4);

the temperature of the pyrolysis in the step (4) is 200-500 ℃.

2. The preparation method of the silicon-carbon anode material for the lithium ion battery according to claim 1, wherein the preparation method comprises the following steps: the silicon particles in the step (1) comprise micron-sized silicon or nano-sized silicon.

3. The preparation method of the silicon-carbon anode material of the lithium ion battery according to claim 1, characterized by comprising the following steps: the speed of high-speed stirring in the step (1) is 3000 rpm.

4. The preparation method of the silicon-carbon anode material for the lithium ion battery according to claim 1, wherein the preparation method comprises the following steps: the spraying head in the step (3) comprises a single needle head or a plurality of needle heads.

5. The preparation method of the silicon-carbon anode material of the lithium ion battery according to claim 1, characterized by comprising the following steps: the pyrolysis time in the step (4) is 2-12h, and the heating rate is 1-10 ℃/min.

6. The preparation method of the silicon-carbon anode material of the lithium ion battery according to claim 1, characterized by comprising the following steps: the inert gas is argon.

7. The preparation method of the silicon-carbon anode material of the lithium ion battery according to claim 1, characterized by comprising the following steps: the hot pressing temperature in the step (5) is 45-85 ℃, the hot pressing time is 5-10min, and the hot pressing pressure is 800-1000 kPa.

8. The preparation method of the silicon-carbon anode material of the lithium ion battery according to claim 1, characterized by comprising the following steps: and (5) pressing the obtained silicon-carbon negative electrode material and a current collector to prepare a negative electrode plate.

9. The preparation method of the silicon-carbon anode material of the lithium ion battery according to claim 8, wherein the preparation method comprises the following steps: and a conductive bonding layer is sprayed on the surface of the current collector, and the spraying thickness is 10-50 mu m.

10. The preparation method of the silicon-carbon anode material of the lithium ion battery according to claim 9, characterized by comprising the following steps: the conductive bonding layer is a mixture of a conductive agent and a bonding agent; the conductive agent comprises one or more of a zero-dimensional nanoparticle conductive agent, a one-dimensional conductive agent and a two-dimensional conductive agent; the binder comprises PVDF, CMC and SBR mixture, polyacrylic acid, polyacrylonitrile or polyacrylate.

11. The preparation method of the silicon-carbon anode material for the lithium ion battery according to claim 10, wherein the preparation method comprises the following steps: the nano-particle conductive agent comprises one or more of SP, acetylene black and Ketjen black; the one-dimensional conductive agent comprises one or two of carbon nano tubes and carbon fibers; the two-dimensional conductive agent is graphene.

12. The use of the lithium ion battery silicon carbon negative electrode material prepared by the method of any one of claims 1 to 11 for preparing a lithium ion battery.