CN115548325A - Silicon negative electrode material and preparation method and application thereof - Google Patents

Abstract

The invention provides a silicon cathode material and a preparation method and application thereof. The silicon cathode material sequentially comprises a nano silicon inner core, an inorganic fast ion conductor transition layer coated on the surface of the nano silicon inner core and a carbon coating layer positioned on the outermost layer from inside to outside, wherein the inorganic fast ion conductor comprises lithium metaaluminate. According to the invention, the lithium metaaluminate (LAO) transition layer is introduced between the nano silicon and the carbon layer, so that the effective modification of the nano silicon material is realized, the nano silicon material is prevented from contacting with direct electrolyte, and the generation of side reaction is avoided; the volume expansion of silicon in the circulation process is inhibited from the material end, and the transition layer simultaneously serves as a buffer layer, so that the volume change is effectively relieved, the structure of the electrode material is more stable, and the electrochemical performance of the material is improved.

Description

Silicon negative electrode material and preparation method and application thereof

Technical Field

The invention belongs to the technical field of secondary batteries, and relates to a silicon negative electrode material, and a preparation method and application thereof.

Background

The silicon material has the advantage of higher theoretical specific capacity as the lithium ion battery cathode, but the silicon is a semiconductor and has poor conductivity, and the volume expansion of the silicon cathode material in use causes the pulverization of the material, thereby causing the poor cycle life of the battery and the rapid capacity attenuation. The huge volume effect and lower conductivity limit the commercial application of silicon cathode technology. It is found that Si particles are dispersed in a matrix of carbon, and the volume change of Si during lithium intercalation and deintercalation can be absorbed by the carbon with high elasticity, thereby improving the cycle performance of the electrode. However, the specific surface area of the nano-particle material is huge, and side reactions with the electrolyte are increased in the circulation process, so that the improvement of the electrochemical performance of the nano-particle material is limited.

The modified coating of silicon is basically direct compounding, lacks the transition layer, and the erosion of electrolyte to silicon still can't be avoided to the at utmost to solitary coating, along with the circulating goes on, and the side reaction constantly takes place, worsens battery performance, is "soft" cladding simultaneously, gets slower the inflation of silicon, and non-active inhibition is not obvious to the volume expansion effect.

CN104617269A discloses a silicon alloy composite negative electrode material, a preparation method and a lithium ion battery, wherein graphite and silicon alloy coated on the surface of the graphite are used as an inner core, a shell is cracked carbon, and the silicon alloy composite negative electrode material with a core-shell structure is prepared by combining nano-compounding, surface modification and coating modification technologies. However, the composite material prepared by the method has high content of metal impurities, is easy to generate self-discharge and has poor high-temperature storage.

Therefore, how to effectively solve the problem of volume expansion of the nano silicon negative electrode material, and simultaneously avoid the corrosion of the electrolyte to silicon, and improve the electrochemical performance of the negative electrode material is a technical problem to be solved urgently.

Disclosure of Invention

The invention aims to provide a silicon negative electrode material and a preparation method and application thereof. According to the invention, a lithium metaaluminate (LAO) transition layer is introduced between the nano silicon and the carbon layer, so that the effective modification of the nano silicon material is realized, the nano silicon material is prevented from directly contacting with an electrolyte, and the generation of side reaction is avoided; the volume expansion of silicon in the circulation process is inhibited from the material end, and the transition layer serves as a buffer layer at the same time, so that the volume change is effectively relieved, the structure of the electrode material is more stable, and the electrochemical performance of the material is improved.

In order to achieve the purpose, the invention adopts the following technical scheme:

in a first aspect, the invention provides a silicon anode material, which sequentially comprises a nano silicon inner core, an inorganic fast ion conductor transition layer coated on the surface of the nano silicon inner core and a carbon coating layer positioned on the outermost layer from inside to outside, wherein the inorganic fast ion conductor comprises lithium metaaluminate.

In the invention, the lithium metaaluminate is used as a transition layer (in-situ grown on the surface of the nano silicon), so that the nano silicon core is prevented from being directly contacted with the electrolyte, and the generation of side reaction is avoided; meanwhile, the hardness of LAO is higher than that of silicon, so that the volume expansion of silicon in the circulation process is inhibited from the material end, and the transition layer serves as a buffer layer at the same time, so that the volume change is effectively relieved, and the electrode material is more stable; the LAO can also provide an effective channel for the transmission of lithium ions, reduce the impedance caused by the thickening of an SEI film in the circulation process, facilitate the de-intercalation behavior of the lithium ions and have better dynamic performance.

In the present invention, if other types of ion conductors are selected, such as aluminum metaphosphate or lithium metaphosphate, incomplete coating and non-uniform structure can occur, because metaphosphate itself has a flocculation effect; if a sulfide electrolyte or other oxide solid electrolyte (such as lithium lanthanum zirconium oxide) is selected, low cost, easy operation, environmental friendliness and the like cannot be realized.

In the invention, the lithium metaaluminate is a single transition layer, but is not directly mixed with the carbon layer to form a layer, and if the lithium metaaluminate is mixed with the carbon layer to form a layer as a coating layer, the transmission of ions and electrons is affected, which is not favorable for performance.

Preferably, the nano-silicon core comprises a porous nano-silicon core.

When the inner core is in a porous nano silicon structure, the volume change caused by charging and discharging can be relieved better, and the service life of the electrode material is prolonged.

Preferably, the thickness of the transition layer of the inorganic fast ion conductor is 1 to 5nm, such as 1nm, 2nm, 3nm, 4nm or 5nm.

In the invention, the effect of preventing the corrosion of the electrolyte to the core porous silicon and inhibiting the volume expansion of the silicon cannot be realized if the thickness of the transition layer of the inorganic fast ion conductor is too thin, and the too thick transition layer can cause the increase of the ion migration path, thereby causing the increase of impedance and being not beneficial to the performance of the material.

In the present invention, the thickness of the carbon coating layer is not limited, and may be adaptively adjusted according to actual requirements, such as a capacity value to be realized or other electrochemical performance requirements.

In a second aspect, the present invention provides a method for preparing a silicon anode material according to the first aspect, the method comprising the steps of:

and mixing a lithium salt solution, an organic aluminum solution and the nano-silicon particles to obtain sol-gel coated with the nano-silicon particles, calcining, and coating with carbon to obtain the silicon negative electrode material.

According to the preparation method provided by the invention, the in-situ coating of the inorganic fast ion conductor (lithium metaaluminate) transition layer on the nano silicon particles is realized through a sol-gel method, compared with pure physical mixed coating, the uniformity and consistency of a coating layer are more facilitated, the gamma crystal form lithium metaaluminate can be obtained only by adopting the sol-gel method, the crystal form cannot be obtained by adopting a common solid phase method, and the uniform in-situ coating is difficult to realize by adopting the common solid phase method for sintering, so that the compact structure cannot be obtained, a buffer layer of electrolyte can be directly isolated, the carbon coating is further realized, and the conductivity of the material is improved; the preparation method provided by the invention has the advantages of simple process and low cost, greatly improves the production efficiency of the cathode material, can better meet the requirement of industrial production, realizes large-scale production, and has great application prospect.

Preferably, the lithium salt solution comprises a lithium acetate solution and/or a lithium carbonate solution, preferably a lithium acetate solution.

In the invention, lithium acetate is used as a reaction raw material, so that the lithium salt can be completely dissolved better, and the subsequent high-temperature calcination gas production phenomenon is avoided.

Preferably, the molar concentration of the lithium salt solution is 1.5 to 2mol/L, such as 1.5mol/L, 1.6mol/L, 1.7mol/L, 1.8mol/L, 1.9mol/L or 2mol/L.

Preferably, the solvent in the lithium salt solution includes absolute ethanol.

Preferably, the D50 of the nano silicon particles is 10 to 100nm, such as 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, 55nm, 60nm, 65nm, 70nm, 75nm, 80nm, 85nm, 90nm, 95nm or 100nm and the like.

In the invention, the D50 of the nano silicon particles is too small, which causes difficult dispersion and easy agglomeration, thus causing nonuniform coating, while the D50 is too large, which affects the service life, multiplying power and cycle performance of the material.

Preferably, the molar concentration of the organic aluminum in the mixed solution of the organic aluminum solution and the nano silicon particles is 0.3 to 0.6mol/L, such as 0.3mol/L, 0.4mol/L, 0.5mol/L or 0.6 mol/L.

Preferably, in the mixed solution of the organic aluminum solution and the nano silicon particles, the molar concentration of the nano silicon particles is 1 to 1.2mol/L, such as 1mol/L, 1.03mol/L, 1.05mol/L, 1.08mol/L, 1.1mol/L, 1.13mol/L, 1.15mol/L, 1.18mol/L or 1.2mol/L.

Preferably, the organoaluminum in the organoaluminum solution comprises aluminum isopropoxide.

Preferably, the solvent in the organoaluminum solution comprises anhydrous ethanol.

Preferably, the nano-silicon particles comprise porous nano-silicon particles.

In the invention, the preparation method of the porous nano silicon particles is a method for obtaining the porous nano silicon material by conventional technical means, the invention is applicable, and exemplarily, the invention provides a preparation method of the porous nano silicon particles, which comprises the following steps:

soaking silicon alloy (aluminum-silicon alloy, magnesium-silicon alloy and the like) in a hydrochloric acid solution with the mass concentration of 5-15% to obtain the porous nano silicon particles.

Preferably, the method of mixing comprises stirring to obtain a sol-gel state.

Preferably, after the mixing, drying is also included.

Preferably, the temperature of the calcination is 500 to 700 ℃, such as 500 ℃, 510 ℃, 520 ℃, 530 ℃, 540 ℃, 550 ℃, 560 ℃, 570 ℃, 580 ℃, 590 ℃, 600 ℃, 610 ℃, 620 ℃, 630 ℃, 640 ℃, 650 ℃, 660 ℃, 670 ℃, 680 ℃, 690 ℃, 700 ℃ or the like.

In the invention, the calcination temperature is too low to obtain the lithium metaaluminate with the target crystal form, and the calcination temperature is too high to cause the loss of lithium salt to be increased, the crystal form of the lithium metaaluminate to be changed and the generation of impurity phases.

Preferably, the calcination time is 3 to 6h, such as 3h, 4h, 5h or 6h.

Preferably, the carbon coating comprises any one of a gas phase carbon coating, a liquid phase carbon coating or a solid phase carbon coating or a combination of at least two of them.

In the present invention, the carbon-coated preparation process is a conventional preparation process, and includes carbon source selection and carbonization temperature, i.e., the present invention is applicable as long as the carbon-coated process of the carbon layer can be obtained.

As a preferable technical scheme, the preparation method comprises the following steps:

stirring a lithium salt solution with the molar concentration of 1.5 to 2mol/L, an aluminum isopropoxide solution and the nano silicon particles to obtain a sol gel for coating the nano silicon particles, drying, calcining at 500 to 700 ℃ for 3 to 6 hours, and coating with gas phase carbon to obtain the silicon anode material;

wherein in the mixed solution of the aluminum isopropoxide solution and the nano silicon particles, the molar concentration of aluminum isopropoxide is 0.3 to 0.6mol/L, and the molar concentration of the nano silicon particles is 1 to 1.2mol/L.

In a third aspect, the present invention also provides a lithium ion battery, which includes the silicon negative electrode material according to the first aspect.

Compared with the prior art, the invention has the following beneficial effects:

(1) According to the invention, the lithium metaaluminate (LAO) transition layer is introduced between the nano silicon and the carbon layer, so that the effective modification of the nano silicon material is realized, the nano silicon material is prevented from contacting with direct electrolyte, and the generation of side reaction is avoided; the volume expansion of silicon in the circulation process is inhibited from the material end, and the transition layer simultaneously serves as a buffer layer, so that the volume change is effectively relieved, the structure of the electrode material is more stable, and the electrochemical performance of the material is improved. When the battery adopts the cathode material provided by the invention, the rate capability can reach more than 90.9%; the capacity retention rate after 300 cycles under 0.1A/g can reach more than 87.5%.

(2) The preparation method provided by the invention has the advantages of simple process and low cost, greatly improves the production efficiency of the cathode material, can better meet the requirement of industrial production, realizes large-scale production, and has great application prospect.

Drawings

Fig. 1 is a schematic flow diagram of the preparation method provided in example 1.

Fig. 2 is an XRD pattern of the silicon anode material provided in example 1.

Fig. 3 is an SEM image of the silicon negative electrode material provided in example 1.

Detailed Description

The technical solution of the present invention is further explained by the following embodiments. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitation of the present invention.

Example 1

The embodiment provides a silicon anode material, which sequentially comprises a nano silicon core, an inorganic fast ion conductor transition layer coated on the surface of the nano silicon core and a carbon coating layer positioned on the outermost layer from inside to outside, wherein the inorganic fast ion conductor is lithium metaaluminate, and the thickness of the inorganic fast ion conductor transition layer is 3.5nm.

The preparation method of the silicon negative electrode material comprises the following steps (the flow is shown in figure 1):

1) Firstly, taking 20mL of absolute ethyl alcohol and 10mL of deionized water by using a measuring cylinder, pouring the absolute ethyl alcohol and the deionized water into a beaker, uniformly stirring and mixing, adding 3.30g (0.05 mol) of lithium acetate into a mixed solvent while stirring, and continuously stirring until the lithium acetate is completely dissolved to obtain a colorless transparent solution A (1.67 mol/L);

weighing 100mL of absolute ethyl alcohol, pouring the absolute ethyl alcohol into a beaker, weighing 10.22g of isopropanol aluminum powder, stirring and adding the isopropanol aluminum powder into the beaker to uniformly disperse the isopropanol aluminum in the ethanol, and then adding 2.80g of porous nano silicon particles (D50 is 50 nm) to obtain a colorless transparent solution B (the molar concentration of the isopropanol aluminum is 0.5mol/L, and the molar concentration of the porous nano silicon particles is 1 mol/L);

2) Adding the solution A into the solution B, continuously stirring for 2h, then transferring the mixed solution into a water bath kettle at 60 ℃ to be dried by distillation (in a solvent gel state), and then drying in a drying oven at constant temperature overnight;

3) Crushing, putting a sample into a muffle furnace, carrying out constant temperature calcination treatment at 600 ℃ for 5h, and carrying out carbon coating on the calcined material by using a CVD (chemical vapor deposition) method to obtain the silicon negative electrode material.

Fig. 2 shows an XRD pattern of the silicon anode material provided in example 1, and fig. 3 shows an SEM pattern of the silicon anode material provided in example 1, and it can be seen from fig. 2 that when the calcination temperature is 600 ℃, the obtained material has a sharp peak shape and a good degree of crystallization, and is an ideal target.

Fig. 3 shows an SEM image of the silicon negative electrode material provided in example 1, as can be seen from fig. 3, the silicon core is continuously and uniformly covered by the lithium metaaluminate transition layer, and an ideal target object of carbon @ lao @ silicon structure is obtained, i.e., the outermost light layer is a carbon layer, the middle dark gray layer is the lithium metaaluminate transition layer, and the inner black layer is the silicon core.

Example 2

The embodiment provides a silicon cathode material, which sequentially comprises a nano-silicon core, an inorganic fast ion conductor transition layer coated on the surface of the nano-silicon core and a carbon coating layer positioned on the outermost layer from inside to outside, wherein the inorganic fast ion conductor is lithium metaaluminate, and the thickness of the inorganic fast ion conductor transition layer is 5nm.

The preparation method of the silicon negative electrode material comprises the following steps:

1) Firstly, taking 20mL of absolute ethyl alcohol and 10mL of deionized water by using a measuring cylinder, pouring the absolute ethyl alcohol and the deionized water into a beaker, uniformly stirring and mixing, adding 3.96g (0.06 mol) of lithium acetate into a mixed solvent while stirring, and continuously stirring until the lithium acetate is completely dissolved to obtain a colorless transparent solution A (2 mol/L);

weighing 100mL of absolute ethanol, pouring the absolute ethanol into a beaker, weighing 12.24g of isopropanol aluminum powder, stirring and adding the isopropanol aluminum powder into the beaker to uniformly disperse the isopropanol aluminum in the ethanol, and then adding 3.22g of porous nano silicon particles (D50 is 100 nm) to obtain a colorless transparent solution B (the molar concentration of the isopropanol aluminum is 0.6mol/L, and the molar concentration of the porous nano silicon particles is 1.15 mol/L);

2) Adding the solution A into the solution B, continuously stirring for 2h, transferring the mixed solution into a water bath kettle at 60 ℃ to be dried by distillation (in a solvent gel state), drying at constant temperature in a drying oven overnight,

3) And crushing, putting the sample into a muffle furnace, carrying out constant temperature calcination treatment at 550 ℃ for 5h, and carrying out carbon coating on the calcined material by using a CVD (chemical vapor deposition) method to obtain the silicon negative electrode material.

Example 3

The embodiment provides a silicon anode material, which sequentially comprises a nano silicon core, an inorganic fast ion conductor transition layer coated on the surface of the nano silicon core and a carbon coating layer positioned on the outermost layer from inside to outside, wherein the inorganic fast ion conductor is lithium metaaluminate, and the thickness of the inorganic fast ion conductor transition layer is 1nm.

The preparation method of the silicon negative electrode material comprises the following steps:

1) Firstly, taking 20mL of absolute ethyl alcohol and 10mL of deionized water by using a measuring cylinder, pouring the absolute ethyl alcohol and the deionized water into a beaker, uniformly stirring and mixing, adding 2.97g (0.045 mol) of lithium acetate into a mixed solvent while stirring, and continuously stirring until the lithium acetate is completely dissolved to obtain a colorless transparent solution A (1.5 mol/L);

weighing 100mL of absolute ethyl alcohol, pouring the absolute ethyl alcohol into a beaker, weighing 6.12g of isopropanol aluminum powder, stirring and adding the isopropanol aluminum powder into the beaker to uniformly disperse the isopropanol aluminum in the ethanol, and then adding 3.08g of porous nano silicon particles (D50 is 80 nm) to obtain a colorless transparent solution B (the molar concentration of the isopropanol aluminum is 0.3mol/L, and the molar concentration of the porous nano silicon particles is 1.1 mol/L);

2) Adding the solution A into the solution B, continuously stirring for 2h, transferring the mixed solution into a water bath kettle at 60 ℃ to be dried by distillation (in a solvent gel state), drying at constant temperature in a drying oven overnight,

3) Crushing, putting a sample into a muffle furnace, calcining at the constant temperature of 600 ℃ for 3h, and carrying out carbon coating on the calcined material by using a CVD (chemical vapor deposition) method to obtain the silicon negative electrode material.

Example 4

This example differs from example 1 in that the calcination temperature in step 3) of this example is 500 ℃.

The remaining preparation methods and parameters were in accordance with example 1.

Example 5

This example differs from example 1 in that the calcination temperature in step 3) of this example is 700 ℃.

The remaining preparation methods and parameters were in accordance with example 1.

Example 6

The difference between this example and example 1 is that the calcination temperature in step 3) of this example is 450 ℃.

The remaining preparation methods and parameters were in accordance with example 1.

Example 7

This example differs from example 1 in that the calcination temperature in step 3) of this example is 800 ℃.

The remaining preparation methods and parameters were in accordance with example 1.

Example 8

The difference between this example and example 1 is that the thickness of the transition layer of the inorganic fast ion conductor in this example is 6nm, and the calcination time in step 3) in the preparation method is 6h.

The remaining preparation methods and parameters were in accordance with example 1.

Example 9

The present embodiment is different from embodiment 1 in that the silicon particles in the present embodiment are non-porous structured nano silicon particles.

The remaining preparation methods and parameters were in accordance with example 1.

Comparative example 1

The difference between the comparative example and the example 1 is that in the silicon anode material provided by the comparative example, no inorganic fast ion conductor transition layer is arranged, and in the preparation method, the porous nano silicon particles are directly subjected to carbon coating.

The remaining preparation methods and parameters were in accordance with example 1.

Comparative example 2

The difference between the comparative example and the example 1 is that the silicon negative electrode material provided by the comparative example is not provided with a carbon coating layer, and the preparation method does not carry out a carbon coating process.

The remaining preparation methods and parameters were in accordance with example 1.

Comparative example 3

The difference between the comparative example and the example 1 is that in the silicon anode material provided by the comparative example, the inorganic fast ion conductor transition layer is not arranged, but lithium metaaluminate is doped in the carbon coating process, namely, the surface of the silicon core is directly coated with a coating layer formed by mixing carbon and lithium metaaluminate (the mass ratio of the lithium metaaluminate in the coating layer is 1.0%).

The remaining preparation methods and parameters were in accordance with example 1.

Comparative example 4

The difference between this comparative example and example 1 is that in this comparative example, the inorganic fast ion conductor is lithium metaphosphate, the raw material and preparation process of lithium metaphosphate in the preparation method refer to the method provided in CN109941981A, and the order of adding silicon is the same as that in example 1.

The rest of the process was identical to example 1.

The silicon negative electrode materials provided in examples 1 to 7 and comparative examples 1 to 4 were used as negative electrode active materials to prepare negative electrode sheets, and the button cells were obtained using lithium sheets as counter electrodes.

Electrochemical performance tests were performed on the batteries provided in examples 1 to 9 and comparative examples 1 to 4, and the results are shown in table 1.

1. And (3) multiplying power testing: the batteries provided in examples and comparative examples were tested in the order of steps (1) to (6):

(1) Charging to 3.0V at a current density of 0.1A/g; discharging to 0.01V at a current density of 0.1A/g for 1 cycle, and performing 5 cycles;

(2) Charging to 3.0V at a current density of 0.2A/g; discharging to 0.01V at a current density of 0.2A/g for 1 cycle, and performing 5 cycles;

(3) Charging to 3.0V at a current density of 0.4A/g; discharging to 0.01V at a current density of 0.4A/g for 1 cycle, and performing 5 cycles;

(4) Charging to 3.0V at a current density of 0.8A/g; discharging to 0.01V at a current density of 0.8A/g for 1 cycle, and performing 5 cycles;

(5) Charging to 3.0V at a current density of 1.6A/g; discharging to 0.01V at a current density of 1.6A/g for 1 cycle, and performing 5 cycles;

(6) Charging to 3.0V at a current density of 0.1A/g; discharging to 0.01V at a current density of 0.1A/g for 1 cycle, and performing 5 cycles;

rate capability: the ratio of the corresponding battery capacity after the discharge in the step (6) to the corresponding battery capacity after the discharge in the step (1);

2. and (3) cycle testing: charging to 3.0V at a current density of 0.1A/g; then, the current density was 0.1A/g, and the discharge was carried out to 0.01V, which was regarded as 1 cycle, and 300 cycles were carried out in total. The retention of the battery capacity after 300 cycles was calculated.

TABLE 1

From the data results of the examples 1 and 6 to 7, it is known that too low calcination temperature results in low synthesis quality of gamma-type lithium metaaluminate, an effective coating layer cannot be formed, corrosion of electrolyte and acceleration of ion transmission cannot be avoided, and too high calcination temperature affects excessive volatilization of lithium salt in the synthesis process, generates various impurity phases, and hinders performance of the battery material.

From the data results of examples 1 and 8, it can be seen that the thickness of the transition layer of the inorganic fast ion conductor is too thick to facilitate the ion transport, resulting in the degradation of the dynamic and cycling performance of the battery.

From the data results of example 1 and example 9, it is known that the porous silicon core can better reduce the swelling effect of the cell itself and improve the electrical properties.

From the data results of example 1 and comparative examples 1-2, it can be seen that the transition layer and the carbon coating layer in the silicon negative electrode material are absent and cannot act together, so that the excellent electrical properties of the battery can be realized.

From the data results of example 1 and comparative example 3, it is understood that the direct mixed coating of carbon and lithium metaaluminate cannot achieve the improvement of the battery material dynamics and deteriorates the cycle to some extent.

As can be seen from the data results of example 1 and comparative example 4, the use of other ion conductors is not favorable for uniform formation of the coating layer, and corrosion of the electrolyte solution to the silicon core cannot be effectively inhibited, resulting in a decrease in cycle performance.

In conclusion, the inorganic fast ion conductor transition layer is coated on the surface of the nano silicon core in situ, and simultaneously, the inorganic fast ion conductor transition layer and the carbon coating layer on the outermost layer act synergistically, so that the effective modification of the nano silicon material is realized, the nano silicon material is prevented from being contacted with direct electrolyte, and the generation of side reactions is avoided; the volume expansion of silicon in the circulation process is inhibited from the material end, and the transition layer serves as a buffer layer at the same time, so that the volume change is effectively relieved, the structure of the electrode material is more stable, and the electrochemical performance of the material is improved. When the battery adopts the cathode material provided by the invention, the rate capability can reach more than 90.9%; the capacity retention rate after 300 cycles under 0.1A.g can reach more than 87.5%.

The applicant declares that the above description is only a specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and it should be understood by those skilled in the art that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are within the scope and disclosure of the present invention.

Claims (10)

1. The silicon cathode material is characterized by sequentially comprising a nano silicon inner core, an inorganic fast ion conductor transition layer coated on the surface of the nano silicon inner core and a carbon coating layer positioned on the outermost layer from inside to outside, wherein the inorganic fast ion conductor comprises lithium metaaluminate.

2. The silicon anode material of claim 1, wherein the nano-silicon core comprises a porous nano-silicon core.

3. The silicon negative electrode material as claimed in claim 1, wherein the thickness of the inorganic fast ion conductor transition layer is 1 to 5nm.

4. A method for preparing a silicon anode material according to any one of claims 1 to 3, characterized in that the method comprises the steps of:

and mixing the lithium salt solution, the organic aluminum solution and the nano-silicon particles to obtain sol-gel coated with the nano-silicon particles, calcining, and coating with carbon to obtain the silicon negative electrode material.

5. The method for preparing the silicon negative electrode material of claim 4, wherein the lithium salt solution comprises a lithium acetate solution and/or a lithium carbonate solution; the molar concentration of the lithium salt solution is 1.5 to 2mol/L.

6. The method for preparing a silicon anode material according to claim 4, wherein the nano silicon particles comprise porous nano silicon particles; the D50 of the nano silicon particles is 10 to 100nm.

7. The method for preparing the silicon negative electrode material as claimed in claim 4, wherein the mixing method comprises stirring to obtain a sol-gel state; and drying is also included after the mixing.

8. The method for preparing the silicon negative electrode material as claimed in claim 4, wherein the calcining temperature is 500 to 700 ℃.

9. The method for preparing the silicon anode material according to claim 4, wherein the method comprises the following steps:

stirring a lithium salt solution with the molar concentration of 1.5 to 2mol/L, an aluminum isopropoxide solution and the nano silicon particles to obtain a sol gel for coating the nano silicon particles, drying, calcining at 500 to 700 ℃ for 3 to 6 hours, and coating with gas phase carbon to obtain the silicon anode material;

wherein in the mixed solution of the aluminum isopropoxide solution and the nano silicon particles, the molar concentration of aluminum isopropoxide is 0.3 to 0.6mol/L, and the molar concentration of the nano silicon particles is 1 to 1.2mol/L.

10. A secondary battery comprising the silicon negative electrode material according to any one of claims 1 to 3.

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