CN115706228A

CN115706228A - Novel silicon-carbon negative electrode material for high-stability high-capacity lithium ion battery and preparation method thereof

Info

Publication number: CN115706228A
Application number: CN202110939993.9A
Authority: CN
Inventors: 黄富强; 张慧敏
Original assignee: Shanghai Lihuang Technology Co ltd
Current assignee: Shanghai Lihuang Technology Co ltd
Priority date: 2021-08-16
Filing date: 2021-08-16
Publication date: 2023-02-17

Abstract

The invention provides a novel silicon-carbon negative electrode material for a high-stability high-capacity lithium ion battery and a preparation method thereof, wherein a multi-component amorphous layer with a mosaic structure is coated on the surface of a silicon active substance through in-situ reaction of a halogen-containing organic carbon source and a lithium salt by one-step cracking, and the multi-component amorphous layer can be mutually and tightly connected with an SiOx (1 < x < 2) layer on the surface of silicon to form a strong conductive sub-network and a strong ion-conducting sub-network, so that the cycling stability of the silicon negative electrode is effectively improved, the implementation process is simple, and the large-scale production is easy.

Description

Novel silicon-carbon negative electrode material for high-stability high-capacity lithium ion battery and preparation method thereof

Technical Field

The invention belongs to the technical field of lithium ion batteries, and particularly relates to a silicon-carbon negative electrode material and a preparation method thereof. The technical problem to be solved is to improve the cycle performance of the silicon-carbon negative electrode material.

Background

As the demand for energy density of lithium ion batteries increases, the existing graphite negative electrodes are difficult to satisfy the future demand. The theoretical specific capacity of silicon to lithium is discharged in the front row of common negative electrode materials and is 4200mAh/g (Li) ₂₂ Si ₅ ) 3579mAh g at room temperature ^-1 (Li ₁₅ Si ₄ ) And the working potential of the silicon is moderate (-0.4V vs Li) ⁺ /Li) is therefore widely recognized as a next generation lithium ion battery negative electrode material with great potential to replace graphite. However, it is not limited toSilicon-based negative electrodes undergo a large volume change (> 300%) during alloying with lithium, and this large volume expansion and contraction causes electrode pulverization, the falling of active materials, and the continuous growth of Solid Electrolyte Interface (SEI) films. Thereby greatly reducing the charge-discharge efficiency, rapidly attenuating the capacity of the lithium ion battery and reducing the cycle stability of the lithium ion battery.

In view of the problems of the silicon cathode, researchers have proposed various promotion strategies, including size nanocrystallization, material composition, composite structure design optimization, and application of novel binders and electrolyte additives. By compounding silicon and a carbon material, on one hand, the electronic conductivity of the whole material is improved, and on the other hand, the composite phase is utilized to provide buffer for volume expansion, so that the cycle stability of the silicon cathode is improved. However, the current carbon compounding strategy which can effectively improve the cycling stability of the silicon cathode is that the capacity of the obtained silicon is less than 800mAh/g and the cycle number is not more than 100 weeks (CN 112652757A, CN 110400914A, CN 111977658A and CN 112768663A) because the compounded carbon material content is higher, or the preparation process is complex and the production is difficult to expand (CN 112331819A and CN 106207177A). The application number CN 106207177A discloses a silicon-carbon negative electrode material containing an artificial SEI layer and having high volume specific capacity and cycle performance, the complicated preparation processes such as ball milling, spray drying, carbonization and the like are required, and the capacity after 300-week cycle is less than 500mAh/g. Application number CN 112331819A discloses a preparation method of a modified silicon-carbon cathode, which is prepared by the processes of preparing a nano-silicon mixed solution, preparing modified nano-silicon, adding a silane coupling agent into the nano-silicon mixed solution and compounding the nano-silicon mixed solution with a carbon source, wherein the capacity of the silicon-carbon cathode can reach 1585mAh/g after 100-week circulation, but the preparation process is complex, the consistency and the difficulty of batch production are high, the cost is high, and the expanded production is difficult to carry out. Application No. CN 112652755A discloses a silicon-carbon negative electrode material and a preparation method thereof, wherein a silicon source is mixed with a carbon source, then the mixture is roasted and then is blended with lithium salt, the reversible capacity is as high as 2500mAh/g, and the lithium salt is physically blended instead of generated in situ in the process, so that the cycle number is less than 50 weeks due to uneven mixing. At present, few reports are available on silicon-carbon negative electrode materials with high cycling stability, high specific capacity and simple preparation process, so that a preparation technology of the silicon-carbon negative electrode material with high capacity and high stability is urgently needed.

Disclosure of Invention

In order to solve the problems in the prior art, the invention provides a preparation method and application of a silicon-carbon composite anode material with high specific capacity and cycling stability. The multi-component amorphous layer with a mosaic structure is coated on the surface of a silicon active substance by one-step cracking of a halogen-containing organic carbon source and a lithium salt through in-situ reaction on the surface of the silicon active substance, and can be reacted with SiO on the surface of silicon _x The layers (x is more than 1 and less than 2) are mutually and tightly connected to form a strong conductive sub-network and a strong ion-conducting sub-network, so that the cycling stability of the silicon cathode is effectively improved, the implementation process is simple, and the large-scale production is easy to realize.

The purpose of the invention is realized by the following technical scheme: a preparation method of a silicon-carbon negative electrode material of a lithium ion battery comprises the following steps:

(1) Mixing a silicon source, a lithium salt and a halogen-containing organic carbon source according to a certain proportion;

(2) And (2) placing the powder obtained in the step (1) in an inert atmosphere or a vacuum environment for high-temperature heat treatment, and cooling to room temperature to obtain the silicon-carbon negative electrode material.

As a preferred scheme, the silicon source is silicon powder, ferrosilicon powder or silicon-calcium alloy powder, and the particle size is 50-5000nm.

Preferably, the lithium salt is one or more of lithium hydroxide, lithium carbonate, lithium nitrate, lithium phosphate, lithium acetate, lithium polyacrylate, lithium acetylacetonate, and the like, and the preferred lithium salt is lithium carbonate.

As a preferable scheme, the organic carbon source containing halogen is one or a mixture of several of polyvinylidene fluoride, polytetrafluoroethylene, perfluoropolyether, polyvinyl chloride, polyvinylidene chloride, and the like, and the preferable organic carbon source containing halogen is polyvinylidene fluoride.

Preferably, the mass ratio of the silicon source to the halogen-containing organic carbon source is 5 to 50.

As a preferable scheme, the temperature is raised to 400-800 ℃ at the speed of 0.5-10 ℃/min in the inert atmosphere, and the heat is preserved and carbonized for 0.5-24 h. The inert atmosphere is one or a mixture of more of high-purity nitrogen, helium, neon and argon.

The method has the advantages of simple and easy process and lower cost, and the silicon-carbon negative electrode material prepared by one-step cracking of the method has the characteristics of good conductivity, high specific capacity, small volume change and the like; the problem of structural damage caused by volume expansion is effectively solved, and the service life and the use safety of the lithium ion battery are improved. Specifically, in the silicon-carbon composite material: the carbon material can buffer the volume change of the silicon cathode in the charging and discharging process and improve the conductivity of the silicon-based material, thereby avoiding the agglomeration of silicon particles in the charging and discharging cycle. Particularly, the multi-component amorphous composite layer generated in situ by the reaction can stabilize the SEI film of the silicon negative electrode, and further improve the cycling stability of the material, so that the silicon-carbon negative electrode material has excellent cycling stability while keeping higher cycling ratio capacity.

Drawings

Fig. 1 is a schematic structural diagram of a silicon-carbon negative electrode material provided by the present invention.

Fig. 2 is an XRD spectrum of the silicon carbon anode material obtained in example 2.

Fig. 3 is a first cycle charge-discharge cycle curve of the silicon-carbon negative electrode material of the lithium ion battery obtained in example 2.

Detailed Description

The present invention will be described in detail with reference to specific embodiments.

Examples 1,

Uniformly mixing 500mg of nano silicon powder (with the average particle size of 100 nanometers), 50mg of polyvinyl chloride and 32mg of hydrated lithium hydroxide to obtain a silicon-carbon composite precursor, then placing the precursor in a tubular furnace filled with high-purity argon, heating to 600 ℃ at the speed of 2 ℃/min, and preserving heat for 10 hours to obtain the LiCl-doped silicon-carbon composite material. The material was subjected to electrochemical performance testing.

Examples 2,

Uniformly mixing 500mg of iron-silicon alloy powder, 50mg of polyvinylidene fluoride and 73mg of lithium carbonate to obtain a silicon-carbon composite precursor, then placing the precursor in a tubular furnace filled with high-purity argon, heating to 750 ℃ at the speed of 2 ℃/min, and preserving heat for 5 hours to obtain the silicon-carbon composite cathode material. The obtained silicon-carbon cathode material is subjected to XRD spectrum detection (as shown in figure 2), and the LiF-doped silicon-carbon composite material can be obtained through detection. The material was subjected to electrochemical performance testing.

Examples 3,

Uniformly mixing 500mg of silicon powder, 25mg of polyvinylidene chloride and 78mg of lithium acrylate to obtain a silicon-carbon composite precursor, then placing the precursor in a tubular furnace filled with high-purity argon, heating to 700 ℃ at the speed of 2 ℃/min, and preserving heat for 2h to obtain the silicon-carbon composite cathode material. And obtaining the LiCl-doped silicon-carbon composite material. The material was subjected to electrochemical performance testing.

Examples 4,

Uniformly mixing 500mg of nano silicon powder, 25mg of polyvinylidene chloride and 50mg of lithium nitrate to obtain a silicon-carbon composite precursor, then placing the precursor in a tubular furnace filled with high-purity argon, heating to 700 ℃ at the speed of 2 ℃/min, and preserving heat for 12h to obtain the silicon-carbon composite cathode material. And obtaining the LiCl-doped silicon-carbon composite material. The material was subjected to electrochemical performance testing.

Examples 5,

Uniformly mixing 500mg of nano silicon powder, 25mg of polyvinylidene fluoride and 68mg of lithium hydroxide to obtain a silicon-carbon composite precursor, then placing the precursor in a tubular furnace filled with high-purity argon, heating to 600 ℃ at the speed of 1 ℃/min, and preserving heat for 15h to obtain the silicon-carbon composite negative electrode material. The LiF doped silicon carbon composite material will be obtained. The material was subjected to electrochemical performance testing.

Examples 6,

Uniformly mixing 500mg of micron silicon powder, 25mg of polytetrafluoroethylene and 45mg of lithium carbonate to obtain a silicon-carbon composite precursor, then placing the precursor in a tubular furnace filled with high-purity argon, heating to 750 ℃ at the rate of 1 ℃/min, and preserving heat for 3h to obtain the silicon-carbon composite negative electrode material. The LiF doped silicon carbon composite material will be obtained. The material was subjected to electrochemical performance testing.

Example 7,

Uniformly mixing 500mg of nano silicon powder, 30mg of polyvinylidene fluoride and 78mg of lithium sulfate to obtain a silicon-carbon composite precursor, then placing the precursor in a tubular furnace filled with high-purity argon, heating to 650 ℃ at the speed of 2 ℃/min, and preserving heat for 8 hours to obtain the silicon-carbon composite negative electrode material. The LiF doped silicon carbon composite material will be obtained. The material was subjected to electrochemical performance testing.

Examples 8,

Uniformly mixing 500mg of silicon powder, 25mg of polyvinyl chloride and 48mg of lithium acrylate to obtain a silicon-carbon composite precursor, then placing the precursor in a tubular furnace filled with high-purity argon, heating to 750 ℃ at the speed of 2 ℃/min, and preserving heat for 2 hours to obtain the silicon-carbon composite cathode material. And obtaining the LiCl-doped silicon-carbon composite material. The material was subjected to electrochemical performance testing.

Examples 9,

And uniformly mixing 500mg of nano silicon powder, 25mg of perfluoropolyether and 50mg of lithium carbonate to obtain a silicon-carbon composite precursor, then placing the precursor in a tubular furnace filled with high-purity argon, heating to 600 ℃ at the speed of 2 ℃/min, and preserving heat for 20 hours to obtain the silicon-carbon composite negative electrode material. The LiF doped silicon carbon composite material will be obtained. The material was subjected to electrochemical performance testing.

Examples 10,

Uniformly mixing 500mg of micron silicon powder, 25mg of polyvinylidene fluoride and 78mg of lithium acrylate to obtain a silicon-carbon composite precursor, then placing the precursor in a tubular furnace filled with high-purity argon, heating to 750 ℃ at the speed of 5 ℃/min, and preserving heat for 10 hours to obtain the silicon-carbon composite negative electrode material. And obtaining the LiF-doped silicon-carbon composite material. The material was subjected to electrochemical performance testing.

Comparative examples 1,

And uniformly mixing 500mg of nano silicon powder and 50mg of polyvinylidene fluoride to obtain a silicon-carbon composite precursor, then placing the precursor in a tubular furnace filled with high-purity argon, heating to 750 ℃ at the speed of 2 ℃/min, and preserving heat for 5 hours to obtain the silicon-carbon composite cathode material. The material was subjected to electrochemical performance testing.

And (3) electrochemical performance testing:

the lithium ion battery negative electrode material half-cell test methods prepared in examples 1 to 3 and comparative example 1 respectively are as follows: uniformly mixing the silicon-carbon composite negative electrode material of the lithium ion battery with a binder CMC (sodium carboxymethylcellulose) and conductive carbon black according to a mass ratio of 80: 10, mixing into slurry, coating on a copper foil, wherein the coating thickness is 100 microns, and drying for 12 hours at 80 ℃ in vacuum to prepare the negative electrode sheet of the lithium battery. The simulated battery is assembled in a glove box filled with argon, electrolyte is 1MLiPFF 6+ EC: DMC = 1: 1 (volume ratio), 5% (volume ratio) FEC, a metal lithium sheet is used as a counter electrode, electrochemical performance test is carried out on a Land battery tester, the charge-discharge voltage range is 0.01-1.5V, and the charge-discharge current is 200mA/g. The test results are listed in the following table.

As can be seen from the above table, all the examples show excellent cycle performance (fig. 3 is a charge-discharge curve of example 2), and the first coulombic efficiency is above 75%, indicating that the silicon-carbon anode material prepared by the present invention has excellent electrochemical performance.

The above description is only a preferred embodiment of the present invention, and is not intended to limit the technical scope of the present invention, so that any minor modifications, equivalent changes and modifications made to the above embodiment according to the technical spirit of the present invention are within the technical scope of the present invention.

Claims

1. A novel silicon-carbon cathode material for a high-stability high-capacity lithium ion battery and a preparation method thereof are characterized in that a multi-component amorphous layer with a mosaic structure is coated on the surface of a silicon active substance through in-situ reaction, and the amorphous layer and SiO on the surface of silicon _x (1 < x < 2) layers interacting and tightly connected to form a strong conductive sub-networkAnd an ion-conducting network, having a high modulus, high ionic and electronic conductivity:

(1) The amorphous layer comprises one or more of carbon, amorphous lithium silicate, amorphous silicon carbide, amorphous lithium carbonate, amorphous lithium phosphate and LiX (X = F, cl), and the thickness of the coating layer is 5-100 nm;

(2) In the structure, the content of silicon active substances is 50-80 wt%, the content of carbon is 5-18wt%, and the content of other lithium salts is 1-5 wt%.

2. The novel silicon-carbon negative electrode material for the high-stability high-capacity lithium ion battery and the preparation method thereof according to claim 1 are characterized in that the structure can be directly prepared by one-step pyrolysis of a mixture of a halogen-containing polymer precursor and a lithium salt, and the specific steps are as follows:

3. The novel silicon-carbon negative electrode material for the high-stability high-capacity lithium ion battery and the preparation method thereof according to claim 2 are characterized in that: the silicon source is one or a combination of silicon powder, ferrosilicon powder or silicon-calcium alloy powder, and the particle size is 50-5000nm.

4. The novel silicon-carbon negative electrode material for the high-stability high-capacity lithium ion battery and the preparation method thereof according to claim 2 are characterized in that: the lithium salt is one or more of lithium hydroxide, lithium carbonate, lithium nitrate, lithium phosphate, lithium acetate, lithium polyacrylate, lithium acetylacetonate and the like.

5. The novel silicon-carbon negative electrode material for the high-stability high-capacity lithium ion battery and the preparation method thereof according to claim 2 are characterized in that: the organic carbon source containing halogen is one or a mixture of several of polyvinylidene fluoride, polytetrafluoroethylene, perfluoropolyether, polyvinyl chloride, polyvinylidene chloride and the like.

6. The novel silicon-carbon negative electrode material for the high-stability high-capacity lithium ion battery and the preparation method thereof as claimed in claim 2, wherein the mass ratio of the silicon source to the organic carbon source containing halogen is 5-50.

7. The novel silicon-carbon anode material for the high-stability high-capacity lithium ion battery and the preparation method thereof as claimed in claim 2, wherein the inert atmosphere is one or a mixture of more of high-purity nitrogen, helium, neon and argon.

8. The novel silicon-carbon anode material for the high-stability high-capacity lithium ion battery and the preparation method thereof according to claim 2 are characterized in that the vacuum degree of a vacuum environment is-10 KPa to-80 KPa.

9. The novel silicon-carbon negative electrode material for the high-stability high-capacity lithium ion battery and the preparation method thereof according to claim 2 are characterized in that: the high-temperature heat treatment conditions are as follows: the heating rate is 0.5-10 ℃/min, the heat treatment temperature is 400-800 ℃, and the heat preservation time is 0.5-24 h.