CN112803014B

CN112803014B - N-type high-conductivity Si-based negative electrode material and preparation method thereof

Info

Publication number: CN112803014B
Application number: CN202110120627.0A
Authority: CN
Inventors: 丁男; 林少雄; 辛昱; 赵宇飞; 许家齐
Original assignee: Hefei Guoxuan High Tech Power Energy Co Ltd
Current assignee: Hefei Gotion High Tech Power Energy Co Ltd
Priority date: 2021-01-28
Filing date: 2021-01-28
Publication date: 2022-05-06
Anticipated expiration: 2041-01-28
Also published as: CN112803014A

Abstract

The invention discloses an n-type high-conductivity Si-based negative electrode material and a preparation method thereof, and relates toThe technical field of lithium ion battery cathode material is Mg₂Si as silicon source and AlBr₃Adding a silicon source, an oxidant and a phosphorus source into a solvent as an oxidant, and adopting a solvothermal method to synthesize the phosphorus-doped n-type high-conductivity Si-based negative electrode material in situ. The phosphorus-doped n-type high-conductivity Si-based negative electrode material is synthesized in situ by adopting a solvothermal method, the synthesis process is carried out at a lower temperature, the reaction is sufficient, the phosphorus doping amount is easy to control, toxic and harmful reagents are not adopted in the preparation, the preparation method is green and safe, and a high-temperature environment is not required. The prepared Si-based material has high purity and high conductivity, the use proportion of a conductive agent can be reduced in the slurry mixing process, and the energy density of the battery is improved; the lithium ion battery cathode material can be used as a cathode material, so that the resistivity can be effectively reduced, more electron transmission channels can be provided, the lithium storage capacity is higher, the rate capability of the battery can be improved, and the polarization can be reduced.

Description

N-type high-conductivity Si-based negative electrode material and preparation method thereof

Technical Field

The invention relates to the technical field of lithium ion battery cathode materials, in particular to an n-type high-conductivity Si-based cathode material and a preparation method thereof.

Background

With the rapid development of electronic products and electric automobiles, the status of lithium ion batteries is increasingly important, and compared with the traditional lead-acid batteries, the lithium ion batteries have the characteristics of high energy density, no memory effect, more cycle times and the like. For electric vehicles, the demand for lithium ion batteries with high energy density and high rate performance is very urgent. Graphite is mostly adopted as the negative electrode of the lithium ion battery at the present stage, and the theoretical specific capacity of the graphite is 375mAh/g and is far less than Si4200 mAh/g; meanwhile, the Si element is the second element contained in the earth crust, the source is rich, and the lithium insertion potential of the Si is higher than that of the graphite, so that the safety is better. Therefore, Si-based anode materials are considered as promising next-generation anode materials, which can replace pure graphite anodes.

In the alloying process of Si and Li, the volume expansion is large, and the electrode material is easy to be pulverized; further, Si itself is a semiconductor material having a resistivity of about 1X 10³Omega cm, and a graphite resistivity of only 8 to 13 x 10^-6Ω · cm, high resistivity limits the charge and discharge rate of Si. The current common solution is to carbon coat Si to reduce resistivity and buffer expansion, butThe above method can only change the resistivity of the Si surface and cannot suppress the expansion.

Doping a Si material with N, P, B or the like to form an n-type or p-type semiconductor can significantly improve the resistivity of Si by electron or hole conduction. The low volume resistivity increases the electron transmission channel of the Si material, and improves the rate capability and the cycle performance. However, the conventional Si doping method mainly includes ball-milling the doping source and Si and then calcining, and the calcining temperature of the method usually exceeds 1000 ℃, Si and the doping source undergo a high-temperature diffusion reaction, but the doping source is easily vaporized and volatilized in a high-temperature environment, and cannot sufficiently react with Si.

Disclosure of Invention

Based on the technical problems in the background art, the invention provides an n-type high-conductivity Si-based negative electrode material and a preparation method thereof, the prepared Si-based material has high conductivity, and the prepared Si-based material can be used as a negative electrode material to effectively reduce the resistivity of a cell and improve the rate capability of the cell.

The invention provides a preparation method of an n-type high-conductivity Si-based negative electrode material, which is characterized in that Mg is used₂Si as silicon source and AlBr₃Adding a silicon source, an oxidant and a phosphorus source into a solvent as an oxidant, and adopting a solvothermal method to synthesize the phosphorus-doped n-type high-conductivity Si-based negative electrode material in situ.

In the present invention, the following reaction occurs:

3Mg₂Si+4AlBr₃→3Si+4Al+6MgBr₂；

the reaction raw materials are also added with a phosphorus source, and phosphorus elements are doped in situ while the Si material is synthesized.

Preferably, the phosphorus source is Na₃PO₄、(NH₄)₃PO₄、(NH₄)₂HPO₄、(NH₄)H₂PO₄One or a combination of several of them.

Preferably, the solvent is cyclohexane.

Preferably, the method comprises the following steps: mixing Mg₂Si、AlBr₃Dissolving phosphorus source in solvent, stirring, transferring to reaction kettle, and feeding under inert atmosphereCarrying out solvothermal reaction; and after the reaction is finished, washing with water, centrifuging, drying, and then carrying out acid washing, water washing and drying.

Preferably, the hydrothermal reaction temperature is 160-200 ℃, and the reaction time is 10-48 h.

Preferably, the phosphorus source and Mg₂Molar ratio of Si is n (P): n (Mg)₂Si)＝0.1-2：1。

Preferably, said Mg₂Si and AlBr₃In a molar ratio of 3: 4-6.

In the present invention, Mg₂Si and AlBr₃Reaction takes place, AlBr₃An appropriate excess may be used.

Preferably, the acid washing is to add the reaction product into acid liquor to stir and wash; preferably, the acid solution is a hydrochloric acid solution.

In the above step, the hydrochloric acid is adopted to wash so as to remove Al and MgBr generated in the reaction₂。

Preferably, the inert atmosphere is nitrogen or argon.

The invention also provides the n-type high-conductivity Si-based negative electrode material prepared by the method.

Has the beneficial effects that: the invention uses Mg₂Si as silicon source and AlBr₃Adding a phosphorus source into a reaction raw material as an oxidant, and adopting a solvothermal method to synthesize a phosphorus-doped n-type high-conductivity Si-based negative electrode material in situ; the synthesis process is carried out at a lower temperature, the reaction is sufficient, the phosphorus doping amount is easy to control, toxic and harmful reagents are not adopted in the preparation, the preparation is green and safe, and a high-temperature environment is not needed. The prepared Si-based material has high purity and high conductivity, the use proportion of a conductive agent can be reduced in the slurry mixing process, and the energy density of the battery is improved; when the lithium ion battery cathode material is used as a cathode material, the resistivity of the battery can be effectively reduced, the battery resistance is reduced, more electron transmission channels are provided, the lithium storage capacity is higher, the multiplying power performance of the battery is further improved, and the polarization is reduced.

Drawings

FIG. 1 is an XRD spectrum of a Si-based material prepared in example 1 of the present invention;

FIG. 2 is an SEM image of a Si-based material prepared in example 1 of the present invention; the scale of the left graph is 100 μm, and the scale of the right graph is 3 μm;

fig. 3 is a charge and discharge curve of a battery in which the Si-based material prepared in example 1 of the present invention and the Si-based material prepared in the comparative example are used for assembly, respectively;

fig. 4 is a rate performance curve of the assembled battery using the Si-based material prepared in example 1 of the present invention and the Si material prepared in the comparative example, respectively.

Detailed Description

The technical means of the present invention will be described in detail below with reference to specific examples.

Example 1

A preparation method of an n-type high-conductivity Si-based negative electrode material comprises the following steps:

1. 0.5g of Mg was taken₂Si、2.6g AlBr₃、0.5g(NH₄)₂HPO₄Adding the mixture into 50ml of cyclohexane solution, uniformly mixing, transferring the mixture into a reaction kettle, introducing nitrogen into the reaction kettle to discharge air, and carrying out heat preservation reaction at 180 ℃ for 24 hours; and (5) washing and drying the sample after the reaction is finished.

2. And (3) putting the dried product into a 50% hydrochloric acid solution, carrying out acid washing and stirring for 6 hours, washing a sample by using deionized water, and drying in a 60 ℃ drying oven to obtain the product to be detected.

The prepared Si-based material is characterized, XRD is shown as figure 1, wherein 'O' represents a standard peak and represents a Si peak in an XRD pattern, and the prepared Si-based material corresponds to a Si spectrogram as can be seen from figure 1; as can be seen from fig. 2, the n-type Si-based material was prepared in the form of spherical particles having a uniform size.

Example 2

1. 0.5g of Mg was taken₂Si、2.4g AlBr₃、1.5g Na₃PO₄Adding into 50ml cyclohexane solution, mixing well, transferring into a reaction kettle, introducing nitrogen into the reaction kettle to exhaust air, and reacting for 48h at 160 ℃; and (5) washing and drying the sample after the reaction is finished.

2. And (3) putting the dried product into a 50% hydrochloric acid solution, carrying out acid washing and stirring for 5 hours, washing a sample by using deionized water, and drying in a 60 ℃ drying oven to obtain the product.

Example 3

1. 0.5g of Mg was taken₂Si、3.4g AlBr₃、2.2g NH₄H₂PO₄Adding into 50ml cyclohexane solution, mixing well, transferring into a reaction kettle, introducing nitrogen into the reaction kettle to exhaust air, and reacting for 10h at 200 ℃; and (5) washing and drying the sample after the reaction is finished.

2. And putting the dried product into a 50% hydrochloric acid solution, pickling and stirring for 8 hours, washing a sample by using deionized water, and drying in a 60 ℃ drying oven to obtain the product.

Comparative example

A preparation method of a Si material comprises the following steps:

1. 0.5g of Mg was taken₂Si、2.6g AlBr₃Adding the mixture into 50ml of cyclohexane solution, uniformly mixing, transferring the mixture into a reaction kettle, introducing nitrogen into the reaction kettle to discharge air, and carrying out heat preservation reaction at 180 ℃ for 24 hours; and (5) washing and drying the sample after the reaction is finished.

2. And (3) putting the dried product into a 50% hydrochloric acid solution, carrying out acid washing and stirring for 6 hours, washing the sample with deionized water after the acid washing, and drying in a 60 ℃ drying oven to obtain the product to be detected.

The resistivity of the Si-based materials prepared in examples 1 to 3 of the present invention and the Si-based materials prepared in the comparative example were measured, and the data are shown in table 1.

TABLE 1 resistivity data for Si-based materials in examples 1-3 and Si material in comparative example

As can be seen from table 1, the resistivity of the phosphorus doped n-type silicon powder is much lower than the intrinsic silicon of the comparative example.

The Si-based materials prepared in the embodiments 1-3 of the invention and the Si materials prepared in the comparative examples are mixed with the artificial graphite according to the mass ratio of 1: 1, preparing a button cell, and detecting the electrochemical performance of the button cell, wherein the results are shown in figures 3 and 4.

As can be seen from FIG. 3, the specific capacity charged to 0.8V in example 1 was 2500mAh/g, which is much higher than the specific capacity 1735mAh/g of intrinsic Si in the comparative example.

As can be seen from fig. 4, the rate performance of example 1 is excellent in the button cell, and the capacity retention of example 1 is 66% and the comparative example capacity retention is only 21% at 1C charging, which is caused by the small resistivity of example 1.

The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be considered to be within the technical scope of the present invention, and the technical solutions and the inventive concepts thereof according to the present invention should be equivalent or changed within the scope of the present invention.

Claims

1. The preparation method of the n-type high-conductivity Si-based negative electrode material is characterized in that Mg is used as the raw material₂Si as silicon source and AlBr₃Adding a silicon source, an oxidant and a phosphorus source into a solvent as an oxidant, and adopting a solvothermal method to synthesize a phosphorus-doped n-type high-conductivity Si-based negative electrode material in situ; the phosphorus source is Na₃PO₄、(NH₄)₃PO₄、(NH₄)₂HPO₄、(NH₄)H₂PO₄One or a combination of more of the above; the solvent is cyclohexane;

the preparation method of the n-type high-conductivity Si-based negative electrode material comprises the following steps: mixing Mg₂Si、AlBr₃Dissolving a phosphorus source and a solvent, uniformly stirring, transferring to a reaction kettle, and carrying out solvothermal reaction under the protection of inert atmosphere; washing with water, centrifuging, drying, acid washing, water washing, and drying to obtain the final product;

the solvent thermal reaction temperature is 160-200 ℃, and the reaction time is 10-48 h;

the Mg₂Si and AlBr₃In a molar ratio of 3: 4-6.

2.The method for preparing an n-type high conductivity Si-based anode material according to claim 1, wherein the phosphorus source and Mg₂Molar ratio of Si is n (P): n (Mg)₂Si) = 0.1-2：1。

3. The method for preparing an n-type highly conductive Si-based anode material according to claim 1, wherein the acid washing is adding the reaction product to an acid solution, stirring and washing; the acid solution is hydrochloric acid solution.

4. The method for preparing an n-type highly conductive Si-based anode material according to claim 1, wherein the inert atmosphere is nitrogen or argon.

5. An n-type high conductivity Si-based negative electrode material prepared by the method of any one of claims 1 to 4.