CN113675392A

CN113675392A - Porous silicon-carbon composite material and preparation method and application thereof

Info

Publication number: CN113675392A
Application number: CN202110857547.3A
Authority: CN
Inventors: 曹军
Original assignee: Sichuan Jiuyuan Core Material Technology Co ltd
Current assignee: Sichuan Jiuyuan Core Material Technology Co ltd
Priority date: 2021-07-28
Filing date: 2021-07-28
Publication date: 2021-11-19
Anticipated expiration: 2041-07-28
Also published as: CN113675392B

Abstract

The embodiment of the invention discloses a porous silicon-carbon composite material which has a core-shell structure, wherein the core is a composite body comprising porous carbon, cerium dioxide and graphene components, and the shell is nano silicon doped with at least one of P, As and Se oxides. The inner core is prepared by spray drying, the shell is coated by ALD multiple alternate deposition of nano-silicon and oxide, and finally the coating is carbonized to obtain the nano-silicon/oxide composite material. Firstly, the charge capacity of the material is improved by utilizing the characteristics of high conductivity and high specific capacity of the raw material, and secondly, the expansion of silicon is restrained in the charge-discharge process by utilizing a porous inner core forming a network structure, so that the cycle performance is improved; thirdly, the ALD coating of the nano-silicon can form a uniform and compact inorganic coating layer, and the coating thickness is easy to control; the silicon is uniformly coated and is not easy to generate side reaction with the electrolyte; the method is beneficial to reducing the specific surface area of the material, improving the cycle life and high-temperature performance of the battery and reducing the gas generation in the battery cycle process.

Description

Porous silicon-carbon composite material and preparation method and application thereof

Technical Field

The invention belongs to the field of lithium ion battery materials, and particularly relates to a porous silicon-carbon composite material.

Background

The silicon-carbon cathode material has the advantages of high specific capacity, wide material source, high safety performance and the like, so the silicon-carbon cathode material is widely applied to the fields of high-end digital and power batteries and the like, but the rate performance and the cycle performance deviation of the lithium ion battery are caused by the defects of poor conductivity, large expansion and the like of silicon-carbon.

One of the measures for improving the multiplying power and the cycle performance of the silicon-carbon material is the coating doping modification of the material. The physical doping is a traditional doping technology, and mainly includes doping graphene, copper and nickel materials with high conductivity on the surface or inside of silicon carbon to improve the conductivity of the composite material and reduce the expansion of the composite material, but as the doped materials and the silicon carbon are combined together through physical adsorption, the poor binding force between the materials is easily caused in the cyclic expansion process. The ALD vapor deposition, that is, depositing amorphous carbon on the surface of graphite, has the characteristics of thin deposition thickness, good consistency, high conductivity, etc., and the process is controllable, and can deposit different materials and different thicknesses according to the requirements of the materials, so as to achieve the customized development of the materials.

Disclosure of Invention

Aiming at the defects of poor conductivity, large expansion rate and the like of the existing silicon-carbon material, the invention provides the porous silicon-carbon composite material.

In order to achieve the technical purpose, the technical scheme adopted by the invention is as follows:

the technical purpose of the first aspect of the invention is to provide a porous silicon-carbon composite material, which has a core-shell structure, wherein the core is a composite body comprising porous carbon, cerium dioxide and graphene components, the shell is nano-silicon doped with at least one compound selected from oxides of P, As and Se, the mass percentage of the shell is 1-20%, preferably 5-10%, based on the total weight of the porous silicon-carbon composite material, the mass percentage of the oxide is 1-5%, preferably 2-4%, based on the total weight of the shell, and the mass ratio of cerium dioxide, porous carbon and graphene in the core is (1-5): 30-50): 0.5-2).

Furthermore, the D50 of the porous silicon-carbon composite material is 2-10 mu m, and the ratio of the diameter of the inner core to the thickness of the outer shell is 100: 5-20.

Further, the oxide of P, the oxide of As and the oxide of Se are respectively P₂O₅、As₂O₃And SeO₂。

The technical purpose of the second aspect of the invention is to provide a preparation method of a porous silicon-carbon composite material, which comprises the following steps:

preparation of the inner core: placing porous carbon, cerium dioxide and graphene in an organic solvent, uniformly mixing, and performing spray drying to obtain an inner core;

preparing a nano silicon shell: depositing nano-silicon on the surface of the inner core by adopting a chemical vapor deposition method, continuously depositing oxide on the surface of the material by adopting the chemical vapor deposition method for at least one compound selected from oxide of P, oxide of As and oxide of Se, and repeating the deposition of the nano-silicon and the oxide to complete 1-100 cycles to obtain the composite material;

carbonizing: carbonizing the composite material.

Further, the organic solvent used in preparing the inner core is selected from at least one of N-methylpyrrolidone, carbon tetrachloride, cyclohexane, xylene, and butanediol.

Furthermore, the mass ratio of cerium dioxide, porous carbon and graphene used in preparing the inner core is (1-5): (30-50): 0.5-2.

Further, the particle size of the porous carbon is 0.2-1.5 mu m, and the specific surface area is 200-400 m²A pore volume of 0.5 to 1.0 cm/g³The pore diameter is 20-100 nm.

Furthermore, when the inner core is prepared, the mass-volume ratio concentration of the total suspended solid in the organic solvent is 15-50 g/100mL, and preferably 20-45 g/100 mL.

Further, when the nano silicon is deposited, the reaction chamber is vacuumized to 20-50 toor and heated to 100-500 ℃, the gasified nano silicon enters the reaction chamber in a pulse mode under the carrying of nitrogen at the flow rate of 10-100 sccm, the nano silicon is adsorbed on the surface of the inner core until the air pressure of the reaction chamber reaches 5-20 toor, and the deposition of the nano silicon is achieved by keeping for 1-120 s.

Further, when the oxide is deposited, the reaction chamber is vacuumized to 50-100 torr, the temperature is heated to 50-300 ℃, the gasified oxide enters the reaction chamber in a pulse mode under the carrying of nitrogen at the flow rate of 10-100 sccm, the oxide is adsorbed on the surface of the inner core until the air pressure of the reaction chamber reaches 5-20 torr, and the deposition and doping of the oxide are achieved by keeping for 1-120 s.

Further, the deposition of the nano silicon and the oxide is preferably completed by 5-50 cycles, and most preferably completed by 5-20 cycles.

Further, the carbonization is carried out for 1-12 hours at 600-1000 ℃ in an inert atmosphere to obtain the porous silicon-carbon composite material. The inert atmosphere is selected from one of nitrogen, helium, neon, argon, krypton or xenon.

The technical purpose of the third aspect of the invention is to provide the application of the porous silicon-carbon composite material as a battery negative electrode material.

The porous silicon-carbon composite material core has a network structure, can restrict the expansion of silicon in the charging and discharging processes, has good cycle performance, and the coating layer formed on the outer layer has controllable thickness, is uniform and compact, reduces the specific surface area of the material, and improves the cycle life and the high-temperature performance of the battery.

The embodiment of the invention has the following beneficial effects:

(1) according to the composite material, the cerium dioxide and the graphene are doped in the porous carbon in the core structure, so that on one hand, the charging capacity of the composite material is improved by utilizing the characteristics of high conductivity and high specific capacity of the material, on the other hand, the porous core with a network structure can be formed by utilizing the compounding of the cerium dioxide, the graphene and the porous carbon, the expansion of silicon is restrained in the charging and discharging process, and the cycle performance is improved; meanwhile, graphene is doped in the graphene, and a network is built in the expansion process of silicon carbon by utilizing the net structure of the graphene, so that an electronic conductive network is formed, the structural collapse of the material is avoided, the water jump is avoided, and the cycle performance is further improved.

(2) The composite material disclosed by the invention coats the nano-silicon by a chemical vapor deposition method, the silicon can uniformly grow on the surface of an inner core, a uniform and compact inorganic matter coating layer can be formed by a few coating times, and the coating thickness is easy to control; the silicon is uniformly coated and is not easy to generate side reaction with the electrolyte; the particles are not agglomerated and are not required to be crushed by adopting a chemical vapor deposition method for coating;

(3) the coating layer formed by the composite material through a chemical vapor deposition method is compact and uniform, the specific surface area of the material is favorably reduced, the cycle life and the high-temperature performance of the battery are improved, and the gas generation in the cycle process of the battery is reduced.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.

Wherein:

FIG. 1 is a flow chart of the preparation steps for examples 1-3;

FIG. 2 SEM image of composite material prepared in example 1.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

In examples 1-3, porous silicon carbon composites were prepared according to the procedure shown in fig. 1:

example 1

S1, preparing an inner core:

adding 3g of cerium dioxide into 100mL of N-methylpyrrolidone to prepare a3 wt% solution, then adding 40g of porous carbon and 50mL of 2 wt% graphene solution, uniformly stirring, and performing spray drying to obtain an inner core; wherein the porous carbon has an average particle diameter of 1 μm and a specific surface area of 300m²Per g, pore volume of 0.8cm³In g, the mean pore diameter is 50 nm.

S2, preparing a nano silicon shell:

transferring the inner core prepared in the step S1 to a substrate of a reaction chamber, vacuumizing the reaction chamber to 30 toar by adopting a chemical vapor deposition method, heating to 300 ℃, gasifying the nano-silicon, and feeding the nano-silicon into the reaction chamber in a pulse mode at the flow rate of 50sccm under the carrying of nitrogen, wherein the nano-silicon is adsorbed on the surface of the inner core until the air pressure of the reaction chamber reaches 10 toar, and keeping the pressure for 60S; the reaction chamber was then adjusted to 80toor, 150 ℃ and P was added₂O₅The oxides are gasified and carried along with the nitrogenPulsed into the reaction chamber at a flow rate of 50sccm, P₂O₅Adsorbing the oxide on the surface of the inner core until the air pressure of the reaction chamber reaches 10toor, keeping the air pressure for 60s to realize P₂O₅Doping of oxide, and repeating the steps₂O₅The deposition is circulated for 10 times to obtain the composite material coated with the shell;

s3, carbonization:

and carbonizing the material obtained in the step S2 at 800 ℃ for 6h in an inert atmosphere to obtain the porous silicon-carbon composite material.

The shell accounts for 8 percent of the total weight of the composite material, and the oxide accounts for 3 percent of the total weight of the shell.

Example 2

S1, preparing an inner core:

adding 1g of cerium dioxide into 100mL of carbon tetrachloride to prepare a1 wt% solution, then adding 30g of porous carbon and 50mL of 1 wt% graphene solution, uniformly stirring, and carrying out spray drying to obtain an inner core; wherein the porous carbon has an average particle diameter of 0.2 μm and a specific surface area of 400m²G, pore volume of 1.0cm³(ii)/g, average pore diameter of 20 nm;

s2, preparing a nano silicon shell:

transferring the inner core prepared in the step S1 to a substrate of a reaction chamber, vacuumizing the reaction chamber to 20 toar by adopting a chemical vapor deposition method, heating to 100 ℃, gasifying the nano-silicon, and feeding the nano-silicon into the reaction chamber in a pulse mode at a flow rate of 10sccm under the carrying of nitrogen, wherein the nano-silicon is adsorbed on the surface of the inner core until the air pressure of the reaction chamber reaches 5 toar, and keeping the pressure for 120S; the reaction chamber was then adjusted to 50toor, 50 ℃ and AS was added₂O₃The oxide is vaporized and pulsed into the reaction chamber, AS, at a flow rate of 10sccm under nitrogen drive₂O₃The oxide is adsorbed on the surface of the inner core until the air pressure of the reaction chamber reaches 20toor, and is kept for 120s, so that AS is realized₂O₃After that, the nano silicon and AS are repeated₂O₃The deposition is circulated for 10 times to obtain the composite material coated with the shell;

s3, carbonization:

Example 3

S1, preparing an inner core:

adding 5g of cerium dioxide into 100mL of cyclohexane to prepare a 5 wt% solution, then adding 50g of porous carbon and 40mL of 5 wt% graphene solution, uniformly stirring, and performing spray drying to obtain an inner core; wherein the porous carbon has an average particle diameter of 1.5 μm and a specific surface area of 200m²Per g, pore volume of 0.5cm³In g, the mean pore diameter is 100 nm.

S2, preparing a nano silicon shell:

transferring the inner core prepared in the step S1 to a substrate of a reaction chamber, vacuumizing the reaction chamber to 50toor by adopting a chemical vapor deposition method, heating to 500 ℃, gasifying the nano-silicon, and feeding the nano-silicon into the reaction chamber in a pulse mode at the flow rate of 50sccm under the carrying of nitrogen, wherein the nano-silicon is adsorbed on the surface of the inner core until the air pressure of the reaction chamber reaches 20toor, and keeping the pressure for 1S; the reaction chamber was then adjusted to 100toor, 300 ℃ and SeO was added₂The oxide was vaporized and pulsed into the reaction chamber, SeO, at a flow rate of 100sccm under nitrogen drive₂The oxide is adsorbed on the surface of the inner core until the air pressure of the reaction chamber reaches 5toor, and is kept for 1s, so that SeO is realized₂Doping of oxide, and repeating the steps₂The deposition is circulated for 10 times to obtain the composite material coated with the shell;

s3, carbonization:

Comparative example 1

Adding 5g of nano-silicon, 30g of porous carbon and 40mL of 5% graphene solution into 200mL of N-methylpyrrolidone, ball-milling for 24h in a ball mill, drying, carbonizing for 6h at 800 ℃ in an inert atmosphere, and crushing to obtain the porous carbon/nano-silicon composite material.

Comparative example 2

According to the same material composition ratio of each component in the embodiment, cerium dioxide, porous carbon and stone are mixedGraphene, nano-silicon and P₂O₅Dispersing the mixture evenly in N-methyl pyrrolidone, ball-milling the mixture for 24 hours, then drying the mixture, carbonizing the mixture for 6 hours at 800 ℃ in an inert atmosphere, and crushing the carbonized mixture to obtain the doped porous carbon/nano silicon composite material.

And (3) performance measurement:

(1) topography testing

SEM tests were performed on the porous silicon carbon composite material of example 1, and the test results are shown in fig. 2. As can be seen from FIG. 2, the material has a spherical structure, and the particle size distribution of the material is uniform and reasonable, and the particle size of the material is between 2 and 8 μm. D50 was tested to be 6.5 μm, the inner core 6.0 μm and the outer shell 0.5 μm.

(2) Button cell test

The composite materials in examples 1-3 and comparative examples 1 and 2 were used as negative electrode materials of lithium ion batteries to assemble button cells, which are respectively marked as A1, A2, A3, B1 and B2.

The preparation method comprises the following steps: adding a binder, a conductive agent and a solvent into a lithium ion battery negative electrode material, stirring and pulping, coating the mixture on copper foil, and drying and rolling to prepare a negative electrode plate; the binder is LA132, the conductive agent is SP, the solvent is NMP, and the dosage ratio of the negative electrode material, SP, PVDF and NMP is 95 g: 1 g: 4 g: 220 mL; LiPF in electrolyte₆A mixture of EC and DEC with a volume ratio of 1:1 is used as an electrolyte; the metal lithium sheet is a counter electrode, and the diaphragm is a polypropylene (PP) film. The button cell was assembled in a hydrogen-filled glove box. The electrochemical performance is carried out on a Wuhan blue electricity CT2001A type battery tester, the charging and discharging voltage range is 0.005V to 2.0V, and the charging and discharging rate is 0.1C.

The test results are shown in table 1.

TABLE 1

As can be seen from the data in table 1, the specific capacity and the first efficiency of the porous silicon-carbon composite material prepared in the example of the present invention are significantly better than those of the comparative examples 1 and 2. The reasons for this may be: the nano-silicon coated on the outer layer is uniformly deposited on the surface of the porous carbon and the interlayer of the porous carbon through ALD, and meanwhile, the carbonized amorphous carbon is coated on the surface of the nano-silicon, so that the direct contact probability of the nano-silicon and electrolyte is reduced, the occurrence of side reaction of the nano-silicon is reduced, and the first efficiency is improved; meanwhile, the material prepared by ALD has high density, so that the tap density is high and the powder conductivity is high.

(3) Testing the soft package battery:

the negative plate is prepared by doping 90% of artificial graphite into the composite materials in examples 1-3 and comparative examples 1 and 2 as a negative electrode material, and NCM532 is used as a positive electrode material; LiPF in electrolyte₆A mixture of EC and DEC with a volume ratio of 1:1 is used as an electrolyte; 5Ah pouch cells, labeled C1, C2, C3, D1, and D2, were prepared with Celgard 2400 membrane as the separator. And respectively testing the liquid absorption and retention capacity, the rebound elasticity and the cycle performance of the negative pole piece.

a. Imbibition ability test

And (3) adopting a 1mL burette, sucking the electrolyte VmL, dripping a drop on the surface of the pole piece, timing until the electrolyte is completely absorbed, recording the time t, and calculating the liquid absorption speed V/t of the pole piece. The test results are shown in table 2.

b. Liquid retention test

Calculating the theoretical liquid absorption amount m of the pole piece according to the pole piece parameters₁And weighing the weight m of the pole piece₂Then, the pole piece is placed in electrolyte to be soaked for 24 hours, and the weight of the pole piece is weighed to be m₃Calculating the amount m of the pole piece liquid absorption₃-m₂And calculated according to the following formula: retention rate ═ m₃-m₂) 100%/m 1. The test results are shown in table 2.

TABLE 2

As can be seen from Table 2, the liquid-absorbing and liquid-retaining abilities of the silicon composite materials obtained in examples 1 to 3 were significantly higher than those of comparative examples 1 and 2. Experimental results show that the porous silicon carbon/nano silicon composite material has high liquid absorption and retention capacity. The reason for this may be: the specific surface of the composite material of the embodiment is larger, so that the liquid absorption and retention capacity of the material is improved.

c. Pole piece rebound rate test

Firstly, testing the average thickness of a pole piece to be D1 by using a thickness gauge, then placing the pole piece in a vacuum drying oven of 80 ℃ for drying for 48h, testing the thickness of the pole piece to be D2, and calculating according to the following formula: the rebound rate was (D2-D1) × 100%/D1. The test results are shown in table 3.

d. Pole piece resistivity testing

The resistivity of the pole piece was measured using a resistivity tester, and the results are shown in table 3.

TABLE 3

As can be seen from the data in table 3, the rebound resilience and resistivity of the negative electrode sheets prepared from the porous silicon-carbon composites obtained in examples 1 to 3 are significantly lower than those of comparative examples 1 and 2, i.e., the negative electrode sheets prepared from the silicon-carbon composites of the present invention have lower rebound resilience and resistivity. The reason for this may be: the porous carbon and the cerium dioxide material are porous structures, so that the expansion of the porous carbon and the cerium dioxide material is reduced, and meanwhile, the electronic conductivity of the cerium dioxide and the graphene material is high, so that the resistivity of the pole piece is reduced.

e. Cycle performance test

The cycle performance of the battery is tested at the temperature of 25 +/-3 ℃ with the charge-discharge multiplying power of 1C/1C and the voltage range of 2.8V-4.2V. The test results are shown in table 4.

TABLE 4

As can be seen from table 4, the cycle performance of the battery prepared from the silicon-carbon composite material of the present invention is significantly better than that of the comparative example, and the reason for this is probably that the pole piece prepared from the silicon-carbon composite material of the present invention has a lower expansion rate, the structure of the pole piece is more stable during the charging and discharging processes, and the cycle performance is improved. In addition, the nano silicon and the amorphous carbon coated on the surface of the silicon-carbon composite material have the characteristics of high density and strong structural stability, and the cycle performance of the nano silicon and the amorphous carbon is also improved.

Claims

1. The porous silicon-carbon composite material is characterized by having a core-shell structure, wherein the core is a composite body comprising porous carbon, cerium dioxide and graphene, the shell is nano-silicon doped with at least one compound selected from oxides of P, As and Se, the mass percent of the shell is 1-20% based on the total weight of the porous silicon-carbon composite material, the mass percent of the oxides is 1-5% based on the total weight of the shell, and the mass ratio of the cerium dioxide, the porous carbon and the graphene in the core is 1-5: 30-50: 0.5-2.

2. The porous silicon-carbon composite material of claim 1, wherein the porous silicon-carbon composite material has a D50 of 2-10 μm and a ratio of the diameter of the inner core to the thickness of the outer shell of 100: 5-20.

3. The porous silicon-carbon composite material according to claim 1, wherein the oxides of P, As and Se are each P₂O₅、As₂O₃And SeO₂。

4. A preparation method of a porous silicon-carbon composite material comprises the following steps:

carbonizing: carbonizing the composite material.

5. The preparation method according to claim 4, wherein the mass ratio of the cerium oxide, the porous carbon and the graphene used in preparing the core is 1-5: 30-50: 0.5-2.

6. The method according to claim 4, wherein the porous carbon has a particle size of 0.2 to 1.5 μm and a specific surface area of 200 to 400m²A pore volume of 0.5 to 1.0 cm/g³The pore diameter is 20-100 nm.

7. The method as claimed in claim 4, wherein the reaction chamber is evacuated to 20to 50 torr during the deposition of the nano-silicon, the temperature is heated to 100to 500 ℃, the gasified nano-silicon is introduced into the reaction chamber in a pulse manner under the carrying of nitrogen at a flow rate of 10to 100sccm, the nano-silicon is adsorbed on the surface of the inner core until the pressure of the reaction chamber reaches 5to 20 torr, and the pressure is maintained for 1 to 120 seconds, thereby realizing the deposition of the nano-silicon.

8. The method as claimed in claim 4, wherein the reaction chamber is evacuated to 50to 100 torr during the deposition of the oxide, the temperature is heated to 50to 300 ℃, the vaporized oxide is introduced into the reaction chamber in a pulse manner under the nitrogen carrying atmosphere at a flow rate of 10to 100sccm, the oxide is adsorbed on the surface of the inner core until the pressure of the reaction chamber reaches 5to 20 torr, and the deposition and doping of the oxide are carried out for 1 to 120 seconds.

9. The preparation method according to claim 4, wherein the deposition of the nano silicon and the oxide is completed by 5to 50 cycles.

10. Use of the porous silicon carbon composite material prepared according to claim 1 or claim 4 as a battery negative electrode material.