CN112803014B - A kind of n-type high conductivity Si-based negative electrode material and preparation method thereof - Google Patents

Abstract

The invention discloses an n-type high-conductivity Si-based negative electrode material and a preparation method thereof, and relates to the technical field of negative electrode materials for lithium ion batteries. Using Mg ₂ Si as a silicon source and AlBr ₃ as an oxidant, the silicon source, the oxidant and the phosphorus The source was added to the solvent, and the phosphorus-doped n-type high-conductivity Si-based anode material was synthesized in situ by a solvothermal method. The invention adopts a solvothermal method to in-situ synthesize a phosphorus-doped n-type high-conductivity Si-based negative electrode material, the synthesis process is carried out at a relatively low temperature, the reaction is sufficient, the phosphorus doping amount is easy to control, and no toxic and harmful substances are used in the preparation. Reagents, green and safe, and do not require high temperature environment. The prepared Si-based material has high purity and high conductivity. During the slurry mixing process, the proportion of conductive agent used can be reduced and the energy density of the battery can be improved; using it as a negative electrode material can effectively reduce the volume resistivity and provide more electrons The transmission channel has a higher lithium storage capacity, thereby improving the battery rate performance and reducing polarization.

Description

A kind of n-type high conductivity Si-based negative electrode material and preparation method thereof

technical field

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

Background technique

With the rapid development of electronic products and electric vehicles, the status of lithium-ion batteries has become increasingly important. Compared with traditional lead-acid batteries, lithium batteries have the characteristics of high energy density, no memory effect, and many cycles. For electric vehicles, there is an urgent need for lithium-ion batteries with high energy density and high rate performance. At present, the negative electrode of lithium ion battery is mostly graphite, and its theoretical specific capacity is 375mAh/g, which is much smaller than Si4200mAh/g; at the same time, Si element is the second most abundant element in the earth's crust, and the source is relatively rich, and the lithium intercalation potential of Si is higher than that of graphite. Its security is also better. Therefore, Si-based anode materials are considered to be the next-generation promising anode materials to replace pure graphite anodes.

During the alloying process of Si and Li, the volume expansion is large, and the electrode material is prone to powdering; in addition, Si itself is a semiconductor material with a resistivity of about 1×10 ³ Ω·cm, while the resistivity of graphite is only 8 ~13×10 ^-6 Ω·cm, the high resistivity limits the charge-discharge rate of Si. At present, the common solution is to carbon-coat Si to reduce the resistivity and buffer expansion, but the above methods can only change the resistivity of the Si surface and cannot suppress the expansion.

The Si material is doped with N, P, B, etc. to form an n-type or p-type semiconductor, and the resistivity of Si can be significantly improved by conducting electrons or holes. The lower bulk resistivity increases the electron transport channel of the Si material and improves the rate capability and cycle performance. However, the traditional Si doping method is mainly to calcine the dopant source and Si after ball milling. The calcination temperature of this method usually exceeds 1000 °C, and the Si and the dopant source undergo a high-temperature diffusion reaction. However, the dopant source is easily vaporized in a high-temperature environment. It volatilizes and cannot fully react with Si.

SUMMARY OF THE INVENTION

Based on the technical problems existing in the background technology, the present invention proposes an n-type high-conductivity Si-based negative electrode material and a preparation method thereof. The prepared Si-based material has high conductivity, and using it as a negative electrode material can effectively reduce the bulk Resistivity, improve battery rate performance.

The preparation method of an n-type high-conductivity Si-based negative electrode material proposed by the present invention uses Mg ₂ Si as the silicon source and AlBr ₃ as the oxidant, adding the silicon source, the oxidant and the phosphorus source into the solvent, and adopts a solvothermal method. In situ synthesis of phosphorus-doped n-type highly conductive Si-based anode materials.

In the present invention, following reaction occurs:

3Mg ₂ Si+4AlBr ₃ →3Si+4Al+6MgBr ₂ ;

A phosphorus source is also added to the reaction raw materials, and phosphorus is doped in-situ when the Si material is synthesized.

Preferably, the phosphorus source is one or a combination of Na ₃ PO ₄ , (NH ₄ ) ₃ PO ₄ , (NH ₄ ) ₂ HPO ₄ and (NH ₄ )H ₂ PO ₄ .

Preferably, the solvent is cyclohexane.

Preferably, it includes the following steps: dissolving Mg ₂ Si, AlBr ₃ and phosphorus source in a solvent, stirring evenly, then transferring to a reaction kettle, and performing a solvothermal reaction under the protection of an inert atmosphere; Pickled and washed with water, and dried.

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

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

Preferably, the molar ratio of Mg ₂ Si and AlBr ₃ is 3:4-6.

In the present invention, Mg ₂ Si and AlBr ₃ react, and AlBr ₃ can be appropriately excessive.

Preferably, the acid washing is adding the reaction product into an acid solution, stirring and washing; preferably, the acid solution is a hydrochloric acid solution.

In the above steps, washing with hydrochloric acid can remove the Al and MgBr ₂ produced by the reaction.

Preferably, the inert atmosphere is nitrogen or argon.

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

Beneficial effects: the present invention uses Mg ₂ Si as the silicon source, AlBr ₃ as the oxidant, and adds the phosphorus source to the reaction raw materials, and adopts the solvothermal method to in-situ synthesize the phosphorus-doped n-type high-conductivity Si-based negative electrode material; The process is carried out at a lower temperature, the reaction is sufficient, the phosphorus doping amount is easy to control, and no toxic and harmful reagents are used in the preparation, which is green and safe, and does not require a high-temperature environment. The prepared Si-based material has high purity and high conductivity. The proportion of conductive agent used can be reduced during the slurry mixing process, and the energy density of the battery can be improved; using it as a negative electrode material can effectively reduce the volume resistivity and reduce the battery resistance. Provide more electron transmission channels and higher lithium storage capacity, thereby improving battery rate performance and reducing polarization.

Description of drawings

Fig. 1 is the XRD spectrum of the Si-based material prepared in Example 1 of the present invention;

Fig. 2 is a SEM image of the Si-based material prepared in Example 1 of the present invention; the scale on the left is 100 μm, and the scale on the right is 3 μm;

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

FIG. 4 is the rate performance curve of the battery in which the Si-based material prepared in Example 1 of the present invention and the Si material prepared in the comparative example are respectively used for assembly.

Detailed ways

Hereinafter, the technical solutions of the present invention will be described in detail through specific embodiments.

Example 1

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

1. Add 0.5g Mg ₂ Si, 2.6g AlBr ₃ , 0.5g (NH ₄ ) ₂ HPO ₄ to 50ml of cyclohexane solution, mix them evenly and transfer to the reaction kettle, feed nitrogen into the reaction kettle to discharge the air, The reaction was incubated at 180 °C for 24 h; after the reaction, the samples were washed and dried.

2. Put the dried product into 50% hydrochloric acid solution, pickle and stir for 6 hours, then use deionized water to wash the sample, and dry it in an oven at 60 °C to obtain the product for testing.

The prepared Si-based material is characterized, and the XRD is shown in Figure 1, in which "O" represents the standard peak, which represents the peak of Si in the XRD pattern. It can be seen from Figure 1 that the prepared Si-based material and Si spectrum It can be seen from Figure 2 that the prepared n-type Si-based material is in the form of spherical particles with uniform size.

Example 2

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

1. Add 0.5g Mg ₂ Si, 2.4g AlBr ₃ and 1.5g Na ₃ PO ₄ into 50ml cyclohexane solution, mix well and transfer to the reaction kettle, feed nitrogen into the reaction kettle to discharge the air, and heat it at 160°C Incubate the reaction for 48h; after the reaction, wash the sample and dry it.

2. Put the dried product into 50% hydrochloric acid solution, pickle and stir for 5 hours, then wash the sample with deionized water, and dry it in an oven at 60°C to obtain the product.

Example 3

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

1. Add 0.5g Mg ₂ Si, 3.4g AlBr ₃ , 2.2g NH ₄ H ₂ PO ₄ into 50ml cyclohexane solution, mix evenly, transfer to the reaction kettle, pass nitrogen into the reaction kettle to discharge the air, The reaction was incubated at 200 °C for 10 h; after the reaction, the samples were washed and dried.

2. Put the dried product into 50% hydrochloric acid solution, pickle and stir for 8 hours, then wash the sample with deionized water, and dry it in an oven at 60°C to obtain the product.

Comparative ratio

A preparation method of Si material, comprising the following steps:

1. Add 0.5g Mg ₂ Si and 2.6g AlBr ₃ to 50ml of cyclohexane solution, mix them evenly, transfer to the reaction kettle, pass nitrogen into the reaction kettle to discharge the air, and keep the reaction at 180°C for 24h; after the reaction is over Wash and dry.

2. Put the dried product into 50% hydrochloric acid solution, pickle and stir for 6 hours, wash the sample with deionized water after the end, and dry it in an oven at 60 °C to obtain the product to be tested.

The resistivity of the Si-based materials prepared in Examples 1-3 of the present invention and the Si materials prepared in the comparative example were tested, and the data are shown in Table 1.

Table 1 Resistivity data of Si-based materials in Examples 1-3 and Si materials in Comparative Examples

It can be seen from Table 1 that the resistivity of the n-type silicon powder doped with phosphorus is much lower than that of the intrinsic silicon of the comparative example.

The Si-based materials prepared in Examples 1-3 of the present invention and the Si materials prepared in the comparative example were mixed with artificial graphite in a mass ratio of 1:1 to make a button battery, and its electrochemical performance was tested. The results are shown in Figures 3 and 4.

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

It can be seen from Figure 4 that in the coin-type battery, the rate performance of Example 1 is excellent. When charging at 1C, the capacity retention rate of Example 1 is 66%, and the capacity retention rate of Comparative Example is only 21%. 1 due to low resistivity.

The above description is only a preferred embodiment of the present invention, but the protection scope of the present invention is not limited to this. The equivalent replacement or change of the inventive concept thereof shall be included within the protection scope of the present invention.

Claims (5)

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.

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