Silicon negative electrode material, preparation method therefor, and use thereof

Abstract

A silicon negative electrode material, a preparation method therefor, and a use thereof, relating to the technical field of secondary batteries. The silicon negative electrode material comprises porous γ-phase lithium aluminate and a carbon coating layer; a carbon layer and a silicon material layer are sequentially deposited in pores of the porous γ-phase lithium aluminate; and the surface of the porous γ-phase lithium aluminate on which the carbon layer and the silicon material layer are deposited is coated with the carbon coating layer. The silicon negative electrode material can effectively prevent the silicon material from being in direct contact with an electrolyte, and suppresses the volume expansion of silicon during circulation from a material end, thereby effectively mitigating the volume change, and making the structure of the electrode material more stable, improving the electrochemical performance of the material.

Description

Silicon negative electrode material and preparation method and application thereof Technical Field

[0001] The present invention belongs to the technical field of secondary batteries, and in particular relates to a silicon negative electrode material and a preparation method and application thereof. Background Art

[0002] Secondary batteries, owing to their high energy density and long cycle life, have been widely used in portable electronic devices and electric vehicles. Silicon, due to its high theoretical capacity and abundant resources, has attracted widespread attention and is considered an ideal candidate for developing anode materials for next-generation secondary batteries with high specific energy and power density. However, silicon's low electrical conductivity and volume expansion during lithium insertion and extraction cycles have limited its application in secondary battery anodes.

[0003] Patent application CN111525108A discloses a method for synthesizing a carbon-coated silicon anode material. This method uses carbon coating to improve the material's conductivity and suppress the volume expansion effect of the silicon-based material during lithium insertion and extraction. However, currently, carbon coating alone does not effectively suppress volume expansion, nor does it effectively prevent electrolyte corrosion of the silicon material, effectively improving battery performance.

[0004] Therefore, how to effectively solve the volume expansion problem of silicon negative electrode materials, while avoiding the corrosion of silicon by the electrolyte and improving the electrochemical performance of the negative electrode materials is a technical problem that needs to be solved urgently. Summary of the Invention

[0005] The purpose of the present invention is to overcome the problems existing in the above-mentioned prior art and provide a silicon negative electrode material and a preparation method and application thereof.

[0006] The present invention is achieved through the following technical solutions:

[0007] The present invention provides a silicon negative electrode material, which includes porous γ-phase lithium aluminate and a carbon coating layer. A carbon layer and a silicon material layer are sequentially deposited in the pores of the porous γ-phase lithium aluminate, and the carbon coating layer is coated on the surface of the porous γ-phase lithium aluminate on which the carbon layer and the silicon material layer are deposited.

[0008] In the silicon negative electrode material of the present invention, an ordered porous γ-phase lithium aluminate is used as a substrate, and a carbon layer and a silicon material layer are sequentially deposited into the pores of the porous γ-phase lithium aluminate. Depositing the carbon layer first can improve the conductivity of the silicon negative electrode material, and then depositing the silicon material. The silicon material is deposited in the pores of the porous γ-phase lithium aluminate, which can effectively alleviate the volume expansion of the silicon material and reduce the release of stress. The pores of the porous γ-phase lithium aluminate can directionally induce the orderly deposition of the silicon material, providing a guarantee for the integrity and uniformity of the carbon coating. Compared with other porous materials, the porous γ-phase lithium aluminate has higher ionic conductivity and higher mechanical strength, which can effectively improve ion conduction and maintain the structure of the material. The present invention realizes the effective modification of nano-silicon materials, prevents them from direct contact with the electrolyte, and avoids the generation of side reactions; suppresses the volume expansion of silicon during the cycle from the material end, effectively alleviates the volume change, makes the structure of the electrode material more stable, and thus improves the electrochemical performance of the material.

[0009] As a preferred embodiment of the silicon negative electrode material of the present invention, the silicon material comprises elemental silicon. In some embodiments, the silicon material layer comprises elemental silicon.

[0010] As a preferred embodiment of the silicon negative electrode material of the present invention, the particle size Dv50 of the elemental silicon is 1 nm-300 nm, preferably 1 nm-100 nm, 1 nm-80 nm, 1 nm-70 nm, 1 nm-60 nm, 1 nm-50 nm, 1 nm-40 nm, 1 nm-30 nm, 1 nm-20 nm, 1 nm-10 nm, or 1 nm-6 nm. Herein, the particle size Dv50 of the elemental silicon can be directionally controlled by conventional CVD deposition methods in the art.

[0011] Preferably, the silicon material layer accounts for 30%-50% of the mass of the silicon negative electrode material.

[0012] As a preferred embodiment of the silicon negative electrode material of the present invention, the pore size of the porous γ-phase lithium aluminate is 1 nm-500 nm.

[0013] When the pore size of the porous γ-phase lithium aluminate is within the above range, it can be adapted to the particle size of silicon materials currently available on the market, so that the silicon negative electrode material has good electrical conductivity.

[0014] Preferably, the carbon source of the carbon coating layer and the deposited carbon layer each independently comprises at least one of an alkane, an alkene, and an alkyne. In some embodiments, the alkane is methane.

[0015] Preferably, the deposition thickness of the carbon layer is 3nm-4nm.

[0016] In the present invention, the thickness of the carbon coating layer is not limited and can be adaptively adjusted according to actual needs, such as the desired capacity value or other electrochemical performance requirements.

[0017] Another object of the present invention is to provide a method for preparing the silicon negative electrode material, comprising the following steps:

[0018] (1) mixing a lithium salt solution, an organoaluminum solution, and a complexing agent uniformly, stirring and evaporating the mixture to obtain a gel;

[0019] (2) freeze-drying the gel obtained in step (1), depositing a carbon layer, and then depositing a silicon material, calcining, and carbon coating to obtain the silicon negative electrode material.

[0020] The present invention prepares porous gamma-phase lithium aluminate through a sol-gel method and freeze-drying. Freeze-drying allows the solvent to be directly sublimed to form a porous structure. The porous gamma-phase lithium aluminate produced by the present invention has a honeycomb-like structure with essentially no distinct flat block structure. This allows subsequent deposition of carbon layers and silicon materials to occur within the pores, thereby improving the electrochemical performance of silicon anode materials.

[0021] As a preferred embodiment of the method for preparing the silicon negative electrode material of the present invention, in step (1), the complexing agent includes at least one of urea, citrate, and hydrazine.

[0022] The complexing agent has the function of forming complex agglomerates, which facilitates the sublimation of the solvent in the middle of the agglomerates during freeze-drying to form a porous structure. The above complexing agents all have good complexing effects. Among them, urea is relatively cheap and is preferred from an economic perspective.

[0023] As a preferred embodiment of the method for preparing the silicon negative electrode material of the present invention, in the step (1), the temperature of the stirring evaporation is 40°C-100°C, preferably 50°C-90°C, 60°C-80°C.

[0024] As a preferred embodiment of the method for preparing the silicon negative electrode material of the present invention, in the step (2), the freeze-drying rate is 2°C / min-10°C / min.

[0025] The freeze-drying rate determines the rate of solvent sublimation. The pore size of γ-phase lithium aluminate can be adjusted by the freeze-drying rate. If the rate is too high, the pore size formed is too large, which may cause the deposition of silicon materials to overlap, affecting the electrochemical performance and the inhibitory effect of volume expansion; if the rate is too low, the pore size formed is too small, which may cause insufficient deposition of silicon materials and fail to achieve the capacity target and volume buffering effect. When the freeze-drying rate is 2℃ / min-10℃ / min, porous γ-phase lithium aluminate with a better pore size can be obtained.

[0026] Preferably, in step (2), the freeze-drying rate is 3°C / min-7°C / min.

[0027] More preferably, when the freeze-drying rate is 3°C / min-7°C / min, porous γ-phase lithium aluminate with more suitable pore size and distribution can be obtained.

[0028] Preferably, the concentration of lithium salt in the lithium salt solution is 1.5 mol / L-1.7 mol / L; the concentration of organoaluminum in the organoaluminum solution is 0.3 mol / L-0.5 mol / L; and the amount of the complexing agent added is 10%-11% of the total mass of the lithium salt and the organoaluminum.

[0029] Preferably, the solvent of the lithium salt solution comprises ethanol and water. Preferably, the solvent of the lithium salt solution comprises anhydrous ethanol and deionized water. Preferably, the solvent of the organoaluminum solution comprises ethanol. Preferably, the solvent of the organoaluminum solution comprises anhydrous ethanol. Preferably, in the solvent of the lithium salt solution, the volume ratio of ethanol to water is (1-5):1, more preferably (1-3):1.

[0030] Preferably, the lithium salt is lithium acetate, and the organoaluminum is aluminum isopropoxide.

[0031] As a preferred embodiment of the method for preparing the silicon negative electrode material of the present invention, in the step (2), the calcination temperature is 300° C.-1000° C., and the calcination time is 1 h-3 h.

[0032] Preferably, in step (2), the calcination temperature is 700°C-900°C.

[0033] In the present invention, the calcination temperature affects the formation of γ-phase lithium aluminate. If the calcination temperature is too low, lithium aluminate with impurity phase will be produced, while if the calcination temperature is too high, the loss of lithium salt will increase and multiple impurity phases will be produced. A calcination temperature of 700°C-900°C is a more suitable condition for preparing porous γ-phase lithium aluminate.

[0034] Preferably, in step (2), the method of performing carbon layer deposition, silicon material deposition, and carbon coating is a CVD method. The first carbon layer deposition is used to form a base within the pores of the porous γ-phase lithium aluminate, and then the silicon material deposition is performed. The silicon material deposition can completely fill the porous structure inside the porous γ-phase lithium aluminate, remove the silicon material outside the pores, and then completely encapsulate the silicon material through carbon coating.

[0035] Another object of the present invention is to provide a secondary battery comprising the silicon negative electrode material or the silicon negative electrode material prepared by the method for preparing the silicon negative electrode material.

[0036] The secondary battery using the silicon negative electrode material of the present invention has higher rate performance and cycle performance.

[0037] The present invention has the following beneficial effects: the silicon negative electrode material of the present invention uses porous γ-phase lithium aluminate as a substrate, and carbon layer deposition can improve the conductivity of the silicon negative electrode material. The porous γ-phase lithium aluminate can effectively alleviate the volume expansion of the silicon material in the pores and reduce the release of stress. It also has higher ionic conductivity and higher mechanical strength, which can effectively improve ion conduction and maintain the structure of the material. The silicon negative electrode material of the present invention can effectively prevent direct contact between the silicon material and the electrolyte, and suppress the volume expansion of silicon during the cycle from the material end, effectively alleviating volume changes, making the structure of the electrode material more stable, and thus improving the electrochemical performance of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] FIG1 is an XRD diffraction pattern of the porous γ-phase lithium aluminate prepared in step (1) of Example 1. DETAILED DESCRIPTION

[0039] To better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments. Those skilled in the art should understand that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0040] Unless otherwise specified, the experimental methods used in the examples are conventional methods; the materials, reagents, etc. used are all available from commercial sources unless otherwise specified.

[0041] The particle size Dv50 of elemental silicon and the pore size of porous γ-phase lithium aluminate were measured by scanning electron microscopy (SEM).

[0042] The thickness of the deposited carbon layer was measured by transmission electron microscopy (TEM).

[0043] The mass fraction of the silicon material layer in the silicon negative electrode material is measured by thermogravimetric analysis (TGA).

[0044] Example 1

[0045] A method for preparing a silicon negative electrode material comprises the following steps:

[0046] (1) Pour 20 mL of anhydrous ethanol and 10 mL of deionized water into a beaker and stir to mix evenly. Add 3.30 g of lithium acetate while stirring and continue stirring until completely dissolved to obtain a colorless and transparent lithium salt solution.

[0047] Pour 100 mL of anhydrous ethanol into another beaker and add 10.12 g of aluminum isopropoxide powder while stirring until the aluminum isopropoxide is evenly dispersed in the ethanol to obtain a colorless, transparent aluminum isopropoxide solution.

[0048] The lithium salt solution was added to the aluminum isopropoxide solution, and 1.35 g of urea as a complexing agent was added. The mixture was stirred continuously for 1 h, and then the mixed solution was transferred to a 60°C water bath and stirred and evaporated to obtain a gel.

[0049] (2) freeze-drying the gel obtained in step (1) at a freeze-drying rate of 5°C / min; after drying, depositing a carbon layer by CVD, then depositing elemental silicon, calcining at a constant temperature of 900°C for 2h, and carbon-coating the calcined material by CVD to obtain the silicon negative electrode material; wherein the carbon sources of the carbon layer material and the carbon coating layer material are both methane.

[0050] The particle size Dv50 of elemental silicon in the silicon negative electrode material of this embodiment is 6 nm; the pore size of the porous γ-phase lithium aluminate is 80 nm-120 nm; the deposition thickness of the carbon layer is 3 nm-4 nm; and the silicon material layer accounts for 43% of the mass of the silicon negative electrode material.

[0051] The gel prepared in step (1) was calcined at 900°C for 2h and then the XRD pattern was tested. As shown in FIG1 , it can be found that the characteristic diffraction peaks (003), (104), and (110) of the sample are relatively obvious and consistent with the standard card. The peaks are sharp and the intensity is high, indicating good crystallinity.

[0052] Example 2

[0053] The main difference between the preparation method of the silicon negative electrode material of this embodiment and that of Example 1 is that in step (2), the calcination temperature is 800° C., and the remaining preparation methods and parameters are consistent with those of Example 1 to obtain the silicon negative electrode material of this embodiment.

[0054] The particle size Dv50 of elemental silicon in the silicon negative electrode material of this embodiment is 6 nm; the pore size of the porous γ-phase lithium aluminate is 80 nm-120 nm; the deposition thickness of the carbon layer is 3 nm-4 nm; and the silicon material layer accounts for 43% of the mass of the silicon negative electrode material.

[0055] Example 3

[0056] The main difference between the preparation method of the silicon negative electrode material of this embodiment and that of Example 1 is that in step (2), the calcination temperature is 700° C., and the remaining preparation methods and parameters are consistent with those of Example 1 to obtain the silicon negative electrode material of this embodiment.

[0057] The particle size Dv50 of elemental silicon in the silicon negative electrode material of this embodiment is 6 nm; the pore size of the porous γ-phase lithium aluminate is 80 nm-120 nm; the deposition thickness of the carbon layer is 3 nm-4 nm; and the silicon material layer accounts for 43% of the mass of the silicon negative electrode material.

[0058] Example 4

[0059] The main difference between the preparation method of the silicon negative electrode material of this embodiment and that of Example 1 is that in step (2), the calcination time is 1 hour, and the remaining preparation methods and parameters are consistent with those of Example 1 to obtain the silicon negative electrode material of this embodiment.

[0060] The particle size Dv50 of elemental silicon in the silicon negative electrode material of this embodiment is 6 nm; the pore size of the porous γ-phase lithium aluminate is 80 nm-120 nm; the deposition thickness of the carbon layer is 3 nm-4 nm; and the silicon material layer accounts for 43% of the mass of the silicon negative electrode material.

[0061] Example 5

[0062] The main difference between the preparation method of the silicon negative electrode material of this embodiment and that of Example 1 is that in step (2), the freeze-drying rate is 3°C / min, and the remaining preparation methods and parameters are consistent with those of Example 1 to obtain the silicon negative electrode material of this embodiment.

[0063] The particle size Dv50 of elemental silicon in the silicon negative electrode material of this embodiment is 6 nm; the pore size of the porous γ-phase lithium aluminate is 40 nm-90 nm; the deposition thickness of the carbon layer is 3 nm-4 nm; and the silicon material layer accounts for 43% of the mass of the silicon negative electrode material.

[0064] Example 6

[0065] The main difference between the preparation method of the silicon negative electrode material of this embodiment and that of Example 1 is that in step (2), the freeze-drying rate is 7°C / min, and the remaining preparation methods and parameters are consistent with those of Example 1 to obtain the silicon negative electrode material of this embodiment.

[0066] The particle size Dv50 of elemental silicon in the silicon negative electrode material of this embodiment is 6 nm; the pore size of the porous γ-phase lithium aluminate is 110 nm-160 nm; the deposition thickness of the carbon layer is 3 nm-4 nm; and the silicon material layer accounts for 43% of the mass of the silicon negative electrode material.

[0067] Example 7

[0068] The main difference between the preparation method of the silicon negative electrode material of this embodiment and that of Example 1 is that in step (2), the calcination temperature is 300° C., and the remaining preparation methods and parameters are consistent with those of Example 1 to obtain the silicon negative electrode material of this embodiment.

[0069] The particle size Dv50 of elemental silicon in the silicon negative electrode material of this embodiment is 6 nm; the pore size of the porous γ-phase lithium aluminate is 80 nm-120 nm; the deposition thickness of the carbon layer is 3 nm-4 nm; and the silicon material layer accounts for 43% of the mass of the silicon negative electrode material.

[0070] Example 8

[0071] The main difference between the preparation method of the silicon negative electrode material of this embodiment and that of Example 1 is that in step (2), the calcination temperature is 1000° C., and the remaining preparation methods and parameters are consistent with those of Example 1 to obtain the silicon negative electrode material of this embodiment.

[0072] The particle size Dv50 of elemental silicon in the silicon negative electrode material of this embodiment is 6 nm; the pore size of the porous γ-phase lithium aluminate is 80 nm-120 nm; the deposition thickness of the carbon layer is 3 nm-4 nm; and the silicon material layer accounts for 43% of the mass of the silicon negative electrode material.

[0073] Example 9

[0074] The main difference between the preparation method of the silicon negative electrode material of this embodiment and that of Example 1 is that in step (2), the freeze-drying rate is 10°C / min, and the remaining preparation methods and parameters are consistent with those of Example 1 to obtain the silicon negative electrode material of this embodiment.

[0075] The particle size Dv50 of elemental silicon in the silicon negative electrode material of this embodiment is 6 nm; the pore size of the porous γ-phase lithium aluminate is 150 nm-190 nm; the deposition thickness of the carbon layer is 3 nm-4 nm; and the silicon material layer accounts for 43% of the mass of the silicon negative electrode material.

[0076] Example 10

[0077] The main difference between the preparation method of the silicon negative electrode material of this embodiment and that of Example 1 is that in step (2), the freeze-drying rate is 2°C / min, and the remaining preparation methods and parameters are consistent with those of Example 1 to obtain the silicon negative electrode material of this embodiment.

[0078] The particle size Dv50 of elemental silicon in the silicon negative electrode material of this embodiment is 6 nm; the pore size of the porous γ-phase lithium aluminate is 35 nm-70 nm; the deposition thickness of the carbon layer is 3 nm-4 nm; and the silicon material layer accounts for 43% of the mass of the silicon negative electrode material.

[0079] Example 11

[0080] The main difference between the preparation method of the silicon negative electrode material of this embodiment and that of Example 1 is that the deposition conditions of the CVD method for depositing elemental silicon are changed to prepare the silicon negative electrode material of this embodiment.

[0081] In the silicon negative electrode material of this embodiment, the particle size Dv50 of elemental silicon is 70 nm; the pore size of the porous γ-phase lithium aluminate is 80 nm-120 nm; the deposition thickness of the carbon layer is 3 nm-4 nm; and the silicon material layer accounts for 43% of the mass of the silicon negative electrode material.

[0082] Comparative Example 1

[0083] A method for preparing a silicon negative electrode material comprises the following steps:

[0084] (1) Pour 20 mL of anhydrous ethanol and 10 mL of deionized water into a beaker and stir to mix evenly. Add 3.30 g of lithium acetate while stirring and continue stirring until completely dissolved to obtain a colorless and transparent lithium salt solution.

[0085] Pour 100 mL of anhydrous ethanol into another beaker and add 10.22 g of aluminum isopropoxide powder while stirring until the aluminum isopropoxide is evenly dispersed in the ethanol to obtain a colorless, transparent aluminum isopropoxide solution.

[0086] The lithium salt solution was added to the aluminum isopropoxide solution, and 1.35 g of urea as a complexing agent was added. The mixture was stirred continuously for 1 h, and then the mixed solution was transferred to a 60°C water bath and stirred and evaporated to obtain a gel.

[0087] (2) The gel obtained in step (1) is calcined at a constant temperature of 900° C. for 2 h, and then a carbon layer is deposited by CVD method, and then elemental silicon is deposited. Finally, the calcined material is carbon-coated by CVD method to obtain the silicon negative electrode material.

[0088] The main difference between this comparative example and Example 1 is that the gel obtained in step (1) is not freeze-dried, and the obtained γ-phase lithium aluminate does not have a porous structure.

[0089] Comparative Example 2

[0090] A method for preparing a silicon negative electrode material comprises the following steps: using a commercially available porous ceramic material, alumina, as a substrate, first depositing a carbon layer by a CVD method, then depositing silicon particles, performing a calcination treatment at a constant temperature of 900°C for 2 hours, and carbon-coating the calcined material by a CVD method to obtain the silicon negative electrode material.

[0091] In the silicon negative electrode material of this embodiment, the particle size Dv50 of elemental silicon is 6 nm; the pore size of the porous ceramic material alumina is 80 nm-120 nm; the deposition thickness of the carbon layer is 3 nm-4 nm; and the silicon material layer accounts for 43% of the mass of the silicon negative electrode material.

[0092] Comparative Example 3

[0093] The main difference between the preparation method of the silicon negative electrode material in this comparative example and that in Example 1 is that in step (2), no carbon layer deposition and no carbon coating are performed, and the remaining preparation methods and parameters are consistent with those in Example 1 to obtain the silicon negative electrode material in this comparative example.

[0094] The particle size Dv50 of elemental silicon in the silicon negative electrode material of this comparative example is 6 nm; the pore size of the porous γ-phase lithium metaaluminate is 80 nm-120 nm; and the silicon material layer accounts for 43% of the mass of the silicon negative electrode material.

[0095] Battery preparation:

[0096] The silicon negative electrode materials of the above examples and comparative examples were prepared into silicon negative electrode sheets, which were further prepared into secondary batteries.

[0097] Specifically, the preparation steps of the silicon negative electrode sheet are as follows: the silicon negative electrode material, polyacrylic acid (PAA), carbon black (SP), and single-walled carbon tubes of the above embodiments and comparative examples are weighed according to a mass percentage of 0.95:0.4:0.95:0.05, mixed and stirred in a beaker for half an hour, then coated on the surface of the copper foil, dried at 60°C in vacuum for 2 hours, and cut into discs with a diameter of 14 mm.

[0098] Specifically, the preparation steps of the secondary battery are: using the silicon negative electrode sheet prepared above as the working electrode, the lithium sheet as the counter electrode, and LiPF6 / EC+DMC+DEC (volume ratio 1:1:1) as the electrolyte, and assembling them into a CR2016 type button battery.

[0099] Electrochemical performance test:

[0100] Rate test: current density 0.1A / g~1.6A / g~0.1A / g, voltage range 0.01V~3.0V, rate performance is the capacity ratio of 0.1A / g after 1.6A / g to the initial 0.1A / g.

[0101] Cycle test: current density 0.1A / g, voltage range 0.01V~3.0V, battery capacity retention after 300 cycles.

[0102] The above electrochemical performance test results are shown in Table 1.

[0103] Table 1: Performance test results of batteries obtained in Examples and Comparative Examples

[0104] It can be seen from the data in Table 1 that the silicon negative electrode material prepared in the embodiment of the present invention has a significant performance improvement when applied to batteries compared with Comparative Examples 1-3. From the data results of Example 1 and Comparative Example 1, it can be seen that since the γ-phase lithium aluminate of Comparative Example 1 is a non-porous structure, the deposited silicon particles are exposed to the outside and react violently with the electrolyte, and its rate and cycle performance are seriously deteriorated. From the data results of Example 1 and Comparative Example 2, it can be seen that the ion transmission capacity and expansion inhibition effect of conventional porous fast ion conductor materials are inferior to those of the porous γ-phase lithium aluminate of the present invention. From the data results of Example 1 and Comparative Example 3, it can be seen that when the carbon layer is not deposited in the pores of the γ-phase lithium aluminate prepared by the present invention and it is not carbon-coated, the conductivity of the silicon negative electrode material is reduced, thereby greatly weakening the rate performance and cycle performance of the secondary battery prepared.

[0105] From the data results of Example 1 and Example 7, it can be seen that if the calcination temperature is too low, impurity phases will be generated, which will lead to low synthesis quality of γ-type lithium aluminate, which is not conducive to improving the rate and cycle performance. From the data results of Example 1 and Example 8, it can be seen that if the calcination temperature is too high, the lithium salt will be excessively volatilized during the synthesis process, and a variety of impurity phases will be generated, which is not conducive to improving the rate and cycle performance. From the data results of Example 1 and Example 9, it can be seen that an excessively high drying rate will lead to a larger pore size and poor uniformity, which will increase the resistance to ion transport and reduce the rate performance; from the data results of Example 1 and Example 10, it can be seen that a too low drying rate will increase the process time and the pore size will be too small, which is not conducive to the deposition of particles. The particles may be exposed and leak out, resulting in a decrease in cycle performance.

[0106] From the data results of Example 1 and Example 11, it can be seen that when the particle size Dv50 of elemental silicon is larger, the rate performance and cycle performance are reduced. However, the rate performance of the battery prepared using the silicon negative electrode material of Example 11 is still much higher than the rate performance of the battery of Comparative Examples 1-3.

[0107] In summary, the silicon negative electrode material of the present invention can effectively improve the electrochemical performance of the battery. When the battery adopts the silicon negative electrode material provided by the present invention, when the current density is from 0.1A / g to 1.6A / g to 0.1A / g for charge and discharge testing in the voltage range of 0.01 to 3.0V, the ratio of the capacity of 0.1A / g after 1.6A / g to the initial 0.1A / g can reach 98.4%; the capacity retention rate after 300 cycles at 0.1A / g can reach 98.2%.

[0108] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A silicon negative electrode material, characterized in that: The silicon negative electrode material includes porous γ-phase lithium aluminate and a carbon coating layer, wherein a carbon layer and a silicon material layer are sequentially deposited in the pores of the porous γ-phase lithium aluminate, and the carbon coating layer is coated on the surface of the porous γ-phase lithium aluminate on which the carbon layer and the silicon material layer are deposited.

2. The silicon negative electrode material according to claim 1, characterized in that: The silicon material layer includes single-element silicon.

3. The silicon negative electrode material according to claim 2, characterized in that: The particle size Dv50 of the elemental silicon is 1nm-300nm.

4. The silicon negative electrode material according to claim 1, characterized in that: The pore size of the porous γ-phase lithium aluminate is 1 nm-500 nm.

5. The silicon negative electrode material according to claim 1, characterized in that: The carbon sources of the carbon coating layer and the deposited carbon layer independently include at least one of alkanes, alkenes and alkynes.

6. A method for preparing the silicon negative electrode material according to any one of claims 1 to 5, characterized in that: The following steps are involved: (1) mixing a lithium salt solution, an organoaluminum solution and a complexing agent uniformly, stirring and evaporating the mixture to obtain a gel; (2) freeze-drying the gel obtained in step (1), depositing a carbon layer, and then depositing a silicon material, calcining, and carbon coating to obtain the silicon negative electrode material.

7. The method for preparing a silicon negative electrode material according to claim 6, characterized in that: In the step (1), the complexing agent includes at least one of urea, citrate, and hydrazine.

8. The method for preparing a silicon negative electrode material according to claim 6, characterized in that: In the step (2), the freeze-drying rate is 2°C / min-10°C / min.

9. The method for preparing a silicon negative electrode material according to claim 6, characterized in that: In the step (2), the calcination temperature is 300°C-1000°C, and the calcination time is 1h-3h.

10. A secondary battery, characterized in that: The invention comprises the silicon negative electrode material according to any one of claims 1 to 5 or the silicon negative electrode material prepared by the method for preparing the silicon negative electrode material according to any one of claims 6 to 9.

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