阅读说明：本技术 一种中空结构硅碳负极材料及其制备方法 (Hollow-structure silicon-carbon negative electrode material and preparation method thereof ) 是由 王汭 于 2021-07-29 设计创作，主要内容包括：本发明属于锂离子电池技术领域,尤其涉及一种中空结构硅碳负极材料及其制备方法,包括硅内核以及包覆在所述硅内核外表面的石墨烯外层,所述硅内核与所述石墨烯外层之间设置有中空层。本发明的一种中空结构硅碳负极材料能够为硅材料的膨胀提供空间,有效缓解了硅碳负极材料在充放电过程中的膨胀导致的容量衰减问题。(The invention belongs to the technical field of lithium ion batteries, and particularly relates to a hollow silicon-carbon negative electrode material and a preparation method thereof. The hollow silicon-carbon negative electrode material can provide space for the expansion of silicon materials, and effectively solves the problem of capacity attenuation caused by the expansion of the silicon-carbon negative electrode material in the charging and discharging processes.)

1. The hollow silicon-carbon cathode material is characterized by comprising a silicon core and a graphene outer layer coated on the outer surface of the silicon core, wherein a hollow layer is arranged between the silicon core and the graphene outer layer.

2. The silicon-carbon anode material with the hollow structure as claimed in claim 1, wherein the diameter of the silicon core is 10-100 um.

3. The silicon-carbon anode material with the hollow structure as claimed in claim 1, wherein the weight ratio of the silicon core to the graphene outer layer is 10-15: 0.5-2.

4. The preparation method of the silicon-carbon anode material with the hollow structure is characterized by comprising the following steps of:

step (A): dissolving a silicon core in a metal solution, adding alkali for reaction, stirring, centrifuging and washing to obtain a first composite particulate matter of a metal deposit coated silicon core;

step (B): adding organic matters into the first composite particles, carrying out condensation reaction under an acidic condition, and carrying out centrifugal washing to obtain second composite particles of organic ester coated silicon cores;

step (C): heating and calcining the second composite particles under the protection of inert gas to graphitize the organic esterified substance to form a graphene outer layer, and cooling to obtain third composite particles;

step (D): and (3) reacting the third composite particles under an acidic condition, removing the metal deposit to form a hollow layer, and thus obtaining the silicon-carbon anode material with the hollow structure.

5. The method for preparing the silicon-carbon anode material with the hollow structure according to claim 4, wherein the silicon inner core in the step (A) is prepared from a silicon source by a high-temperature pyrolysis method or a vapor deposition method.

6. The method for preparing a silicon-carbon anode material with a hollow structure as claimed in claim 5, wherein the silicon source is one of silicon tetrahydride, dimethyldichlorosilane, and trimethyldichlorosilane.

7. The method for preparing the silicon-carbon anode material with the hollow structure according to claim 4, wherein the metal solution in the step (A) is one of a zinc ion solution, a magnesium ion solution and an iron ion solution.

8. The preparation method of the hollow-structure silicon-carbon anode material according to claim 4, wherein the concentration of the metal solution in the step (A) is 0.8-2 mol/L.

9. The preparation method of the hollow-structure silicon-carbon anode material according to claim 4, wherein the organic substance in the step (B) is one of stearic acid isopropanol, phenylacetic acid and porphyrin.

10. The preparation method of the silicon-carbon anode material with the hollow structure as claimed in claim 4, wherein the condensation reaction in the step (B) is carried out at a temperature of 70-90 ℃ for 0.5-2 hours.

11. The preparation method of the hollow-structure silicon-carbon anode material as claimed in claim 4, wherein the calcination temperature in the step (C) is 500-700 ℃, and the calcination time is 1-4 hours.

Technical Field

The invention belongs to the technical field of lithium ion batteries, and particularly relates to a hollow silicon-carbon negative electrode material and a preparation method thereof.

Background

The lithium ion battery is widely applied to the fields of electronic equipment, electric appliances, electric automobiles and the like as an efficient, light and portable energy storage device. At present, graphite (370mAhg) with lower specific capacity is mostly adopted as a negative active material of the commercial lithium ion battery, and silicon (Li) with higher theoretical specific capacity₁₅Si₄3590mAhg) is very suitable for preparing a high-performance lithium ion battery as a negative electrode material. As electric vehicles pursue higher driving range, more and more battery manufacturers aim to silicon carbon negative electrodes with higher gram capacity. However, the silicon carbon negative electrode material is easy to cause volume expansion (300%) in the charging and discharging processes, so that the negative electrode is broken, and the cycle life is further reduced, thereby limiting the application of the silicon carbon negative electrode.

Disclosure of Invention

The invention aims to: aiming at the defects of the prior art, the provided silicon-carbon negative electrode material with the hollow structure can provide space for the expansion of silicon materials, and effectively relieves the problem of capacity attenuation caused by the expansion of the silicon-carbon negative electrode material in the charging and discharging process.

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

the utility model provides a hollow structure silicon carbon negative electrode material, includes silicon core and cladding the graphite alkene of silicon core surface is outer, the silicon core with be provided with the hollow layer between the graphite alkene skin.

As an improvement of the hollow silicon-carbon cathode material, the diameter of the silicon inner core is 10-100 um.

As an improvement of the hollow silicon-carbon cathode material, the weight part ratio of the silicon inner core to the graphene outer layer is 10-15: 0.5-2.

The second purpose of the invention is: aiming at the defects of the prior art, the preparation method of the silicon-carbon anode material with the hollow structure is provided, is simple to operate, has good controllability and can be produced in large batch.

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

a preparation method of a hollow-structure silicon-carbon anode material comprises the following steps:

step (A): dissolving a silicon core in a metal solution, adding alkali for reaction, stirring, centrifuging and washing to obtain a first composite particulate matter of a metal deposit coated silicon core;

step (B): adding organic matters into the first composite particles, carrying out condensation reaction under an acidic condition, and carrying out centrifugal washing to obtain second composite particles of organic ester coated silicon cores;

step (C): heating and calcining the second composite particles under the protection of inert gas to graphitize the organic esterified substance to form a graphene outer layer, and cooling to obtain third composite particles;

step (D): and (3) reacting the third composite particles under an acidic condition, removing the metal deposit to form a hollow layer, and thus obtaining the silicon-carbon anode material with the hollow structure.

As an improvement of the preparation method of the hollow structure silicon-carbon anode material, in the step (A), the silicon inner core is prepared from a silicon source by a high-temperature pyrolysis method or a vapor deposition method.

As an improvement of the preparation method of the hollow silicon-carbon negative electrode material, the silicon source is one of silicon tetrahydride, dimethyldichlorosilane and trimethyldichlorosilane.

As an improvement of the preparation method of the hollow silicon-carbon anode material of the present invention, in the step (a), the metal solution is one of a zinc ion solution, a magnesium ion solution, and an iron ion solution.

As an improvement of the preparation method of the hollow silicon-carbon anode material, the concentration of the metal solution in the step (A) is 0.8-2 mol/L.

As an improvement of the preparation method of the hollow silicon-carbon anode material, the organic matter in the step (B) is one of stearic acid isopropanol, phenylacetic acid and porphyrin.

As an improvement of the preparation method of the hollow silicon-carbon cathode material, the condensation reaction in the step (B) is carried out at 70-90 ℃ for 0.5-2 hours.

As an improvement of the preparation method of the hollow silicon-carbon cathode material, the calcination temperature in the step (C) is 500-700 ℃, and the calcination time is 1-4 hours.

Compared with the prior art, the invention has the beneficial effects that: the hollow silicon-carbon cathode material is provided with the hollow layer, so that an expansion space can be provided for a silicon material, and the capacity attenuation caused by the expansion of the silicon-carbon cathode material in the charging and discharging processes is effectively relieved.

Drawings

Fig. 1 is a schematic structural diagram of a hollow silicon carbon anode material of the present invention.

FIG. 2 is a flow chart of the preparation of the hollow silicon carbon anode material of the invention.

Wherein: 1. a silicon core; 2. an outer layer of graphene.

Detailed Description

1. The utility model provides a hollow structure silicon carbon negative electrode material, includes silicon core 1 and cladding and is in the outer 2 of graphite alkene of 1 surface of silicon core, silicon core 1 with be provided with the hollow layer between the outer 2 of graphite alkene.

The hollow silicon-carbon cathode material is provided with the hollow layer, so that an expansion space can be provided for a silicon material, and the capacity attenuation caused by the expansion of the silicon-carbon cathode material in the charging and discharging processes is effectively relieved.

Preferably, the silicon core 1 has a diameter of 10-100 um. The diameter of the silicon inner core 1 is too large, the graphene outer layer 2 is easily broken in the expansion process, and the gram specific capacity provided by the silicon inner core 1 is small due to too small diameter.

Preferably, the weight part ratio of the silicon inner core 1 to the graphene outer layer 2 is 10-15: 0.5-2. The weight portion ratio of the silicon inner core 1 to the graphene outer layer 2 is controlled, so that the hollow silicon-carbon material formed by combination is more stable.

2. A preparation method of a hollow-structure silicon-carbon anode material comprises the following steps:

step (A): dissolving a silicon core 1 in a metal solution, adding alkali for reaction, stirring, centrifuging and washing to obtain a first composite particulate matter of a metal deposit coated silicon core 1;

step (B): adding the composite particles into an organic matter, carrying out condensation reaction under an acidic condition, centrifuging and washing to obtain second composite particles of organic esterified matter coated silicon inner cores 1;

step (C): heating and calcining the second composite particles under the protection of inert gas to graphitize the organic esterified substance to form a graphene outer layer 2, and cooling to obtain third composite particles;

step (D): and (3) reacting the third composite particles under an acidic condition, removing the metal deposit to form a hollow layer, and thus obtaining the silicon-carbon anode material with the hollow structure.

The preparation method of the hollow structure silicon-carbon cathode material comprises the steps of firstly depositing metal deposits on the surface of a silicon core 1, reacting on the surface of the metal deposits to generate organic esterified substances, graphitizing the obtained reactant to enable the organic esterified substances to form a graphene outer layer 2, and etching under an acidic condition to remove the metal deposits to obtain a hollow layer, so that the hollow structure silicon-carbon cathode material is prepared.

Preferably, the silicon core 1 in step (a) is prepared from a silicon source by a high temperature pyrolysis method or a vapor deposition method. The silicon core 1 obtained by pyrolysis or vapor deposition is of higher purity and provides a higher specific gram capacity.

Preferably, the silicon source is one of silicon tetrahydride, dimethyldichlorosilane and trimethyldichlorosilane. Silicon tetrahydride, dimethyldichlorosilane, and trimethyldichlorosilane are used as a silicon source, and reduction and oxidation are easily performed to form a silicon core 1 having high purity.

Preferably, the metal solution in step (a) is one of a zinc ion solution, a magnesium ion solution and an iron ion solution. The metal solution is firstly deposited on the surface of the silicon inner core 1, and provides a generating contact point of organic matters, so that organic ester is generated on the outer surface of the metal deposit, thereby forming a coating outer layer, and the metal solution can be used as an intermediate reactant in the process, and can be a solution for generating deposition under alkaline conditions, such as a zinc ion solution, a magnesium ion solution, an iron ion solution and the like, preferably, a zinc ion solution is used.

Preferably, the concentration of the metal solution in the step (A) is 0.8-2 mol/L. The metal solution is used as an intermediate reactant, the metal solution reacts to generate metal deposits on the surface of the silicon core 1, the thicker the metal solution is, the thicker the layer formed by the metal deposits is, the larger the finally generated hollow layer is, and the capacity causes the collapse of the graphene outer layer 2 at the outermost layer, so that the silicon-carbon negative electrode material is crushed; the lower the concentration of the metal solution, the thinner the layer formed by the metal deposit, the smaller the hollow layer finally formed, which is disadvantageous to the expansion of silicon and deteriorates the capacity.

Preferably, the organic substance in the step (B) is one of stearic acid isopropanol, phenylacetic acid and porphyrin. The organic matter can react on the branched chain group of the metal deposit, so that the organic matter is connected to the surface of the metal deposit, and the subsequent graphitization is facilitated to form the graphene layer. Preferably, the organic substance has a certain molecular weight, which is beneficial to forming a certain amount of graphene layer after subsequent graphitization.

Preferably, the condensation reaction in the step (B) is carried out at a temperature of 70-90 ℃ for 0.5-2 hours. The temperature and time of the condensation reaction are well controlled, so that the organic ester is generated more uniformly, the molecular weight is in a certain range, and the subsequent formation of the thickness of the graphene layer is facilitated.

Preferably, the calcining temperature in the step (C) is 500-700 ℃, and the calcining time is 1-4 hours. The temperature and time of graphitization calcination are controlled, so that the graphene layer with good uniformity and consistency can be formed.

The present invention will be described in further detail with reference to the following detailed description and the accompanying drawings, but the embodiments of the invention are not limited thereto.

Example 1

A preparation method of a silicon-carbon cathode material with a hollow structure, as shown in figure 2,

1. with SiH₄Preparing Si balls with the diameter of 20um, namely a silicon inner core 1, for a silicon source through a high-temperature pyrolysis method; the obtained Si pellets were dissolved in 15ml of 1mol/L ZnCl₂In solution, then the5mL of concentrated ammonia water was slowly added to Si and ZnCl₂Continuously stirring the mixed solution, centrifuging and washing the obtained solution to obtain Si/ZnO balls, namely first composite particles;

3. the resulting Si/ZnO pellets were mixed with 2mL of stearic acid isopropyl alcohol in H₂SO₄Reacting in the solution at 80 ℃ in a water bath for 1h, centrifuging and washing the solution to obtain Si/ZnO @ stearic acid isopropanol beads, namely second composite particles;

4. calcining the obtained Si/ZnO @ stearic acid isopropanol pellets in a tubular furnace at the temperature of 600 ℃ for 2 hours in a nitrogen atmosphere, and naturally cooling to obtain Si/ZnO @ graphene pellets, namely third composite particles;

5. the obtained Si/ZnO @ graphene pellets are put in H₂SO₄Etching the solution for 1h at the temperature of 60 ℃, and removing ZnO in the small ball intermediate layer to obtain hollow Si @ graphene small balls, namely the hollow silicon carbon cathode material.

The silicon-carbon cathode material with the hollow structure comprises a silicon core 1 and a graphene outer layer 2 coated on the outer surface of the silicon core 1, wherein a hollow layer is arranged between the silicon core 1 and the graphene outer layer 2, as shown in fig. 1. Wherein the weight part ratio of the silicon inner core 1 to the graphene outer layer 2 is 10: 1.

(1) Preparation of positive plate

Uniformly mixing NCM811 positive active material, conductive agent superconducting carbon, carbon tubes and adhesive polyvinylidene fluoride according to the mass ratio of 96:2.0:0.5:1.5 to prepare positive slurry, coating the positive slurry on one surface of a current collector aluminum foil, drying and rolling at 85 ℃, coating and drying the positive slurry on the other surface of the aluminum foil according to the method, and then carrying out cold pressing treatment on the prepared pole piece with the positive active material layers coated on the two surfaces of the aluminum foil; and (4) trimming, cutting into pieces, slitting, and slitting to obtain the lithium ion battery positive plate.

(2) Preparation of negative plate

Preparing the hollow silicon-carbon negative electrode material, conductive agent superconducting carbon, thickener carboxymethylcellulose sodium and binder styrene butadiene rubber into negative electrode slurry according to the mass ratio of 96.5:1.0:1.0:1.5, coating the negative electrode slurry on a current collector copper foil, drying and rolling at 85 ℃, coating and drying the negative electrode slurry on the other side of the copper foil according to the method, and then carrying out cold pressing treatment on the prepared pole piece with the negative electrode active material layer coated on the two sides of the copper foil; and trimming, cutting into pieces, slitting, and slitting to obtain the lithium ion battery negative plate.

(3) A diaphragm: a polyethylene porous film with a thickness of 7 μm was selected as the separator.

(4) Preparing an electrolyte:

mixing lithium hexafluorophosphate (LiPF)₆) Dissolving in a mixed solvent of dimethyl carbonate (DEC), Ethylene Carbonate (EC), Ethyl Methyl Carbonate (EMC) and diethyl carbonate (DEC) (the mass ratio of the three is 3:5:2) to obtain the electrolyte.

(5) Preparing a battery:

and winding the positive plate, the diaphragm and the negative plate into a battery cell, wherein the battery cell capacity is about 5 Ah. The diaphragm is positioned between the adjacent positive plate and negative plate, the positive electrode is led out by aluminum tab spot welding, and the negative electrode is led out by nickel tab spot welding; then the electric core is placed in an aluminum-plastic packaging bag, the electrolyte is injected after baking, and finally the polymer lithium ion battery is prepared after the processes of packaging, formation, capacity grading and the like.

Example 2

The difference from the embodiment 1 is that:

the diameter of the silicon core 1 is 40 um.

The rest is the same as embodiment 1, and the description is omitted here.

Example 3

The difference from the embodiment 1 is that:

the diameter of the silicon core 1 is 60 um.

The rest is the same as embodiment 1, and the description is omitted here.

Example 4

The difference from the embodiment 1 is that:

the diameter of the silicon core 1 is 100 um.

The rest is the same as embodiment 1, and the description is omitted here.

Example 5

The difference from the embodiment 1 is that:

the diameter of the silicon core 1 is 10 um.

The rest is the same as embodiment 1, and the description is omitted here.

Example 6

The difference from the embodiment 1 is that:

the concentration of the metal solution was 2 mol/L.

The rest is the same as embodiment 1, and the description is omitted here.

Example 7

The difference from the embodiment 1 is that:

the concentration of the metal solution was 1.5 mol/L.

The rest is the same as embodiment 1, and the description is omitted here.

Example 8

The difference from the embodiment 1 is that:

the concentration of the metal solution was 0.5 mol/L.

The rest is the same as embodiment 1, and the description is omitted here.

Example 9

The difference from the embodiment 1 is that:

the concentration of the metal solution was 0.1 mol/L.

The rest is the same as embodiment 1, and the description is omitted here.

Comparative example 1

The difference from the embodiment 1 is that:

preparing a negative plate:

preparing graphite, conductive agent superconducting carbon, thickener carboxymethylcellulose sodium and binder styrene butadiene rubber into negative electrode slurry according to the mass ratio of 96.5:1.0:1.0:1.5, coating the negative electrode slurry on a current collector copper foil, drying and rolling the current collector copper foil at 85 ℃, coating and drying the negative electrode slurry on the other side of the copper foil according to the method, and then carrying out cold pressing treatment on the prepared pole piece with the negative electrode active material layer coated on the two sides of the copper foil; and trimming, cutting into pieces, slitting, and slitting to obtain the lithium ion battery negative plate.

The rest is the same as embodiment 1, and the description is omitted here.

Performance testing

1. And (3) testing the cycle performance: charging the lithium ion secondary battery to 4.25V at a constant current of 1C at 25 +/-2 ℃, then charging to 0.05C at a constant voltage of 4.25V, standing for 5min, and then discharging to 2.8V at a constant current of 1C, wherein the process is a charge-discharge cycle process, and the discharge capacity of the time is the discharge capacity of the first cycle. The lithium ion secondary battery was subjected to 100-cycle charge and discharge tests in accordance with the above-described method, and the discharge capacity per cycle was recorded, and the test results are shown in table 1.

The cycle capacity retention (%) was the discharge capacity at the 200 th cycle/the discharge capacity at the first cycle × 100%.

2. Testing the thickness expansion rate of the pole piece: at 25 ℃, the lithium ion battery is charged to 4.45V at a constant current of 1C, then charged at a constant voltage until the current is 0.05C, and then discharged to 3.0V at a constant current of 1C, which is the first cycle. The lithium ion battery was cycled 20 times according to the above conditions. The thickness of the pole piece before and after the cycle was measured with a micrometer, and the measurement results are shown in table 1. The pole piece thickness expansion ratio was calculated by the following formula:

the expansion rate of the thickness of the pole piece is [ (thickness after cycle-thickness before cycle)/thickness before cycle ] × 100%.

TABLE 1

Item	Capacity retention (%)	Thickness expansion ratio (%)	Item	Capacity retention (%)	Thickness expansion ratio (%)
						Example 1	86	1.1	Example 2	85	1.3
Example 3	85	1.4	Example 4	84	1.4
						Example 5	85	1.3	Example 6	84	1.4
Example 7	83	1.4	Example 8	85	1.5
						Example 9	85	1.6	Comparative example 1	63	3.6

As can be seen from table 1, the negative electrode sheet prepared from the hollow silicon-carbon negative electrode material of the present invention more effectively inhibits the expansion of the silicon-carbon negative electrode than the conventional negative electrode sheet of comparative example 1, and the prepared battery has a higher capacity retention rate and a lower thickness expansion rate, and has a longer service life and better safety. From comparison of examples 1 to 5, when the diameter of the silicon core 1 is set to be 20um, the capacity retention rate of the prepared battery reaches 86%, the thickness expansion rate is 1.1%, and the performance is better, because the weight part ratio of the silicon core 1 to the graphene outer layer 2 at the diameter is close to 10:1, a more stable structure can be formed. As shown by comparing examples 1 and 6 to 9, when the concentration of the metal solution is set to be 1mol/L, the prepared battery has better performance, because the concentration of the metal solution affects the thickness of the metal precipitate of the hollow silicon-carbon negative electrode material, i.e. the thickness of the hollow layer, i.e. the distance between the silicon core 1 and the graphene outer layer 2, and thus the structural stability of the whole silicon-carbon negative electrode material is affected. Since the weight part ratio of the silicon core 1 to the metal deposit in example 1 is 10:1, the two comparisons show that, when the weight part ratio of the silicon core 1 to the metal deposit layer to the graphene outer layer 2 is 10:1:1, the prepared structure is more stable and the performance is better.

Variations and modifications to the above-described embodiments may also occur to those skilled in the art, which fall within the scope of the invention as disclosed and taught herein. Therefore, the present invention is not limited to the above-mentioned embodiments, and any obvious improvement, replacement or modification made by those skilled in the art based on the present invention is within the protection scope of the present invention. Furthermore, although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.