CN111740084B

CN111740084B - Sulfur-doped pre-lithiated silicon-carbon composite material and preparation method thereof

Info

Publication number: CN111740084B
Application number: CN202010540999.4A
Authority: CN
Inventors: 许晓落; 庞成志; 魏智伟; 安静
Original assignee: Shanxi Shangtai Lithium Technology Co ltd; Shijiazhuang Shangtai Technology Co Ltd
Current assignee: Shanxi Shangtai Lithium Technology Co ltd; Shijiazhuang Shangtai Technology Co Ltd
Priority date: 2020-06-15
Filing date: 2020-06-15
Publication date: 2021-11-23
Anticipated expiration: 2040-06-15
Also published as: CN111740084A

Abstract

The invention relates to a sulfur-doped pre-lithiated silicon-carbon composite material and a preparation method thereof. The preparation method comprises the following steps: adding an organic sulfur compound into the graphene oxide solution, and uniformly stirring to obtain a solution a; adding organic lithium and an organic solvent into the solution a, sealing and uniformly stirring to obtain a solution b; adding silicon monoxide into the solution b, uniformly stirring, heating and pressurizing to react, filtering, and drying to obtain a composite material intermediate; and (3) putting the composite material intermediate into an inert atmosphere for carbonization, and obtaining the sulfur-doped pre-lithiated silicon-carbon composite material after the carbonization. By doping organic sulfur and organic lithium in the silicon monoxide, the invention forms lithium silicate to improve the first efficiency of the material, and simultaneously forms a-Li-S-structure and a-CO-NH-structure to improve the structural stability and specific capacity of the material and improve the cycle performance of the material.

Description

Sulfur-doped pre-lithiated silicon-carbon composite material and preparation method thereof

Technical Field

The invention belongs to the field of lithium ion battery preparation, and particularly relates to a sulfur-doped pre-lithiated silicon-carbon composite material and a preparation method thereof.

Background

With the improvement of the energy density requirement of the lithium ion battery, the negative electrode material is required to have high energy density and electrochemical performance thereof, and the silicon-carbon material is applied to the field of the high energy density battery due to the characteristics of high specific capacity and the like, but the silicon-carbon material has the defects of poor conductivity, large expansion, low initial efficiency, poor cycle and the like, so that the application of the silicon-carbon material is limited.

Disclosure of Invention

In order to solve the problems in the prior art, the invention provides a sulfur-doped pre-lithiated silicon-carbon composite material and a preparation method thereof. Aiming at the defects of poor electronic conductivity, poor structural stability caused by expansion in the circulation process, poor circulation performance and the like of the existing silicon-carbon material, the invention dopes organic sulfur and organic lithium in the silicon monoxide, and simultaneously forms a structure of Li-S-to improve the structural stability and specific capacity of the material and improve the circulation performance of the material while forming lithium silicate to improve the first efficiency of the material.

The scheme of the invention is to provide a preparation method of a sulfur-doped pre-lithiated silicon-carbon composite material, which comprises the following steps:

(1) adding an organic sulfur compound into the graphene oxide solution, and uniformly stirring to obtain a solution a;

(2) adding organic lithium and an organic solvent into the solution a obtained in the step (1), and sealing and uniformly stirring to obtain a solution b;

(3) adding silicon monoxide into the solution b obtained in the step (2), uniformly stirring, heating and pressurizing to react, filtering, and drying to obtain a composite material intermediate;

(4) and (4) putting the composite material intermediate obtained in the step (3) into an inert atmosphere for carbonization, and obtaining the sulfur-doped pre-lithiation silicon-carbon composite material after the carbonization.

Preferably, in the step (1), the organic sulfur compound is one of methionine, cysteine or 2-mercaptoethanol.

Preferably, in the step (1), the concentration of the graphene oxide solution is 0.1-1 wt.%; the ratio of hydroxyl and carboxyl in the graphene oxide is 0.5-2%.

Preferably, in the step (2), the organolithium is one of methyllithium, lithium n-butoxide, n-butyllithium or tert-butyllithium.

Preferably, in step (2), the organic solvent is N-methylpyrrolidone.

Preferably, the weight ratio of the organic sulfur compound, the graphene oxide, the organic lithium and the organic solvent is 10: 0.1-1: 1-5: 100.

Preferably, the weight ratio of the silicon monoxide to the solution b is 100: 100-500.

Preferably, in the step (3), the heating temperature is 100-200 ℃, the pressurizing pressure is 1-5 Mpa, and the reaction time is 1-24 hours.

Preferably, in the step (4), the carbonization temperature is 800-1100 ℃, and the carbonization time is 1-12 h.

Based on the same technical concept, the invention further provides the sulfur-doped pre-lithiated silicon-carbon composite material prepared by the preparation method.

The design idea of the invention is as follows:

one of the methods for improving the conductivity of the silicon-carbon material is to dope the high-conductivity graphene and other conductivity materials, and simultaneously dope and modify the high-conductivity graphene and other conductivity materials to improve the specific capacity and reduce the expansion of the high-conductivity graphene and other conductivity materials.

The invention has the beneficial effects that:

according to the preparation method of the sulfur-doped pre-lithiated silicon-carbon composite material, the specific capacity of the material is improved and the expansion of the material is reduced by using sulfur, the electronic conductivity of the material is improved by using graphene, the irreversible capacity loss of the material is reduced by using lithium silicate formed by organic lithium and silicon monoxide, and the first efficiency of the composite material is improved. Meanwhile, sulfur in the organic compound and organic lithium form a-Li-S-structure, so that the structural stability of the material can be improved. Through hydrothermal reaction, silicon monoxide can be uniformly doped among compounds with a structure of-Li-S-, and a formed complex has the characteristics of high structural stability, high first-time efficiency, high specific capacity and the like. Meanwhile, the structure of the-CO-NH-structure formed by the acid groups such as hydroxyl, carboxyl and the like on the surface of the graphene oxide and the amino group on the surface of the organic sulfur compound through chemical reaction has the characteristic of stable structure, and the structural stability of the material is improved.

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.

FIG. 1 is a scanning electron micrograph of a sulfur-doped prelithiated silicon carbon composite prepared in accordance with example 1 of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention will be described in detail below. It is to be understood that the described embodiments are merely exemplary of the invention, and not restrictive of the full scope of the invention. All other embodiments, which can be derived by a person skilled in the art from the examples given herein without any inventive step, are within the scope of the present invention.

Example 1

The embodiment provides a preparation method of a sulfur-doped pre-lithiated silicon-carbon composite material, which comprises the following steps:

(1) adding 10g of methionine into 100g of graphene oxide N-methyl pyrrolidone solution with the concentration of 0.5 wt.%, and uniformly stirring to obtain a solution a; wherein, the ratio of hydroxyl and carboxyl in the graphene oxide is 1 percent.

(2) Adding 3g of tert-butyl lithium and 100g N-methyl pyrrolidone solvent into the solution a obtained in the step (1), and sealing and uniformly stirring to obtain a solution b;

(3) adding 100g of silicon monoxide into 300g of the solution b, uniformly stirring, transferring into a high-pressure reaction kettle, reacting for 12 hours at 180 ℃ and 3Mpa, sequentially filtering, and drying at 80 ℃ for 12 hours to obtain a composite material intermediate;

(4) and (4) transferring the composite material intermediate obtained in the step (3) to a tubular furnace, heating to 900 ℃ at a heating rate of 5 ℃/min in an argon inert atmosphere for carbonization for 6h, and then naturally cooling to room temperature to obtain the sulfur-doped pre-lithiated silicon-carbon composite material.

Example 2

(1) adding 10g of cysteine into 100g of graphene oxide N-methyl pyrrolidone solution with the concentration of 0.1 wt.%, and uniformly stirring to obtain a solution a; wherein, the ratio of hydroxyl and carboxyl in the graphene oxide is 0.5 percent.

(2) Adding 1g of lithium n-butoxide and 100g of carbon tetrachloride solvent into the solution a obtained in the step (1), and sealing and uniformly stirring to obtain a solution b;

(3) adding 100g of silicon monoxide into 100g of the solution b, uniformly stirring, transferring into a high-pressure reaction kettle, reacting for 24 hours at 100 ℃ and 1Mpa, sequentially filtering, and drying at 80 ℃ for 12 hours to obtain a composite material intermediate;

(4) and (4) transferring the composite material intermediate obtained in the step (3) to a tubular furnace, heating to 800 ℃ at a heating rate of 5 ℃/min in an argon inert atmosphere, carbonizing for 12h, and naturally cooling to room temperature to obtain the sulfur-doped pre-lithiated silicon-carbon composite material.

Example 3

(1) adding 10g of 2-mercaptoethanol into 100g of graphene oxide N-methylpyrrolidone solution with the concentration of 1 wt.%, and uniformly stirring to obtain a solution a; wherein, the ratio of hydroxyl and carboxyl in the graphene oxide is 2 percent.

(2) Adding 5g of n-butyllithium and 100g of tetrahydrofuran solvent into the solution a obtained in the step (1), and sealing and uniformly stirring to obtain a solution b;

(3) adding 100g of silicon monoxide into 500g of the solution b, uniformly stirring, transferring the solution to a high-pressure reaction kettle, reacting for 1h at 200 ℃ and 5Mpa, sequentially filtering, and drying at 80 ℃ for 12h to obtain a composite material intermediate;

(4) and (4) transferring the composite material intermediate obtained in the step (3) to a tubular furnace, heating to 1100 ℃ at a heating rate of 5 ℃/min in an argon inert atmosphere, carbonizing for 1h, and naturally cooling to room temperature to obtain the sulfur-doped pre-lithiated silicon-carbon composite material.

Comparative example

The comparative example provides a preparation method of a silicon-carbon composite material, comprising the following steps:

adding 100g of silicon monoxide and 100g of graphene oxide N-methyl pyrrolidone solution with the concentration of 1 wt.% into 100g of tetrahydrofuran, uniformly stirring, transferring into a high-pressure reaction kettle, reacting for 12h at the temperature of 180 ℃ and the pressure of 3Mpa, filtering, vacuum drying at the low temperature of 80 ℃ for 12h, transferring into a tubular furnace, heating to 900 ℃ at the heating rate of 5 ℃/min under the inert atmosphere of argon, carbonizing for 6h, and naturally cooling to room temperature to obtain the silicon monoxide/carbon composite material.

Examples of the experiments

(1) Scanning Electron Microscope (SEM) testing

Fig. 1 is an SEM image of the sulfur-doped pre-lithiated silicon-carbon composite material prepared in example 1, and it can be seen from fig. 1 that the sulfur-doped pre-lithiated silicon-carbon composite material of example 1 has a particle size of 5 to 10 μm and a uniform and reasonable size distribution.

(2) Physicochemical property test and button cell performance test

The specific surface area, tap density and powder conductivity of the composite material prepared according to the test examples and comparative examples of the national standard GB/T-245131-2009 graphite cathode materials for lithium ion batteries are shown in Table 1.

The preparation method comprises the following steps of respectively taking the sulfur-doped pre-lithiated silicon-carbon composite material obtained in the examples 1-3 and the silicon monoxide/carbon composite material obtained in the comparative example as negative electrode materials to prepare the pole piece, and specifically comprises the following steps: weighing 9g of negative electrode material, 0.5g of conductive agent SP and 0.5g of LA132 binder, adding into 220ml of deionized water, stirring uniformly, coating on a copper foil to prepare a membrane,then, LiPF with a lithium sheet as a negative electrode, celegard2400 as a diaphragm and electrolyte solute of 1mol/L₆The button cell is assembled in a glove box with the content of oxygen and water lower than 0.1ppm to form the button cell, the button cell is arranged on a blue tester, the button cell is charged and discharged at the rate of 0.1C, the voltage range is 0.05V-2.0V, and the button cell is stopped after circulation for 3 weeks. The results of the button cell performance tests are shown in table 1.

TABLE 1 comparison of physicochemical and performance test results for button cell

As can be seen from table 1, the sulfur-doped pre-lithiated silicon-carbon composite materials obtained in examples 1 to 3 are superior to comparative examples in terms of the first efficiency and the first discharge capacity thereof, because the pre-lithiation reduces the loss of the irreversible capacity thereof to improve the first efficiency thereof, and the sulfur doping improves the specific capacity thereof; the density of the material can be improved by adopting the hydrothermal reaction, so that the tap density of the material can also be improved; in the sulfur-doped pre-lithiated silicon-carbon composite material obtained in the embodiment, the organic lithium and silicon form lithium silicate, so that the electronic conductivity of the material is improved, and the powder conductivity of the material is improved.

(3) Manufacturing of soft package battery

And (3) doping 90% of artificial graphite into the sulfur-doped pre-lithiated silicon-carbon composite material obtained in the examples 1-3 and the silicon monoxide/carbon composite material obtained in the comparative example to serve as negative electrode materials, and preparing a negative electrode piece. With ternary materials (LiNi)_1/3Co_1/3Mn_1/ ₃O₂) As the positive electrode, LiPF₆(the solvent is EC + DEC, the volume ratio is 1:1, and the concentration is 1.3mol/l) is used as electrolyte, and celegard2400 is a diaphragm to prepare 5Ah soft package batteries C1, C2, C3 and D. And then testing the cycle performance and the rate capability of each soft package battery and the expansion rate of the pole piece of each soft package battery.

(3.1) Pole piece thickness test

Testing the expansion rate of the pole piece: the method comprises the steps of firstly testing the thickness D1 of a negative pole piece of the soft package battery after constant volume, then circulating for 100 times and fully charging the soft package battery, then testing the thickness D2 of the negative pole piece of the soft package battery after the soft package battery is dissected, and then calculating the expansion rate (D2-D1)/D1. The results are shown in Table 2.

TABLE 2 comparison of pole piece thickness for examples and comparative examples

	D1/μm	D2/μm	Expansion ratio (D2-D1)/D1
				Example 1	105	137	30.5％
Example 2	104	137	31.5％
				Example 3	106	140	32.5％
Comparative example	105	148	40.5％

It can be seen from table 2 that the expansion rate of the negative electrode plate prepared by using the sulfur-doped pre-lithiated silicon-carbon composite material obtained in the example is significantly smaller than that of the comparative example, because the lithium silicate contained in the material of the example can relieve the expansion in the charging and discharging processes, and the chemical bond structures of the-Li-S-and-CO-NH-in the sulfur-doped pre-lithiated silicon-carbon composite material have the advantage of firm combination, and the expansion rate can be reduced.

(3.2) cycle Performance test

And carrying out cycle test on the soft package lithium ion battery under the conditions that the charge and discharge voltage is 2.5-4.2V, the temperature is 25 +/-3.0 ℃ and the charge and discharge multiplying power is 0.5C/0.5C, and the test results are shown in Table 3.

TABLE 3 comparison of the cycles of the examples and comparative examples

Examples	Initial capacity retention (%)	Capacity retention rate (%). about 500 times
			Example 1	100	93.3
Example 2	100	93.0
			Example 3	100	92.7
Comparative example	100	88.1

As can be seen from table 3, the cycle performance of the soft-packed lithium ion battery prepared by using the sulfur-doped pre-lithiated silicon-carbon composite material obtained in the example is superior to that of the comparative example at each stage of the cycle, because the sulfur-doped pre-lithiated silicon-carbon composite material obtained in the example can increase the amount of lithium ions in the charging and discharging process by means of sufficient lithium ions, and the pre-lithiated material structure formed at the same time has a small expansion force, so that the cycle performance of the pre-lithiated silicon-carbon composite material can be improved.

(3.3) Rate Performance test

Conditions of rate performance test: the charging and discharging voltage is 2.5-4.2V, the temperature is 25 +/-3.0 ℃, the charging multiplying factor is 1.0C, and the discharging multiplying factor is 1.0C, 2.0C, 3.0C and 5.0C. The results of the rate performance test are shown in table 4.

TABLE 4 comparison of Rate Properties of examples and comparative examples

It can be seen from table 4 that the rate capability of the soft-packed lithium ion battery using the sulfur-doped pre-lithiated silicon carbon composite material obtained in the example is significantly better than that of the comparative example, because the sulfur-doped pre-lithiated silicon carbon composite material obtained in the example contains lithium silicate, which provides sufficient lithium ions during the charging and discharging process, thereby improving the high rate capability thereof.

The above description is only for the specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present invention, and all the changes or substitutions should be covered within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the appended claims.

Claims

1. The preparation method of the sulfur-doped prelithiation silicon-carbon composite material is characterized by comprising the following steps of:

(1) adding an organic sulfur compound into the graphene oxide solution, and uniformly stirring to obtain a solution a; the organic sulfur compound is one of methionine, cysteine or 2-mercaptoethanol; the concentration of the graphene oxide solution is 0.1-1 wt.%; the ratio of hydroxyl and carboxyl in the graphene oxide is 0.5-2%;

(2) adding organic lithium and an organic solvent into the solution a obtained in the step (1), and sealing and uniformly stirring to obtain a solution b; the organic lithium is one of n-butyl alcohol lithium, n-butyl lithium or tert-butyl lithium; the organic solvent is one of N-methyl pyrrolidone, carbon tetrachloride or tetrahydrofuran;

(3) adding SiO into the solution b obtained in the step (2) and uniformly stirring, wherein the weight ratio of the SiO to the solution b is 100: 100-500; heating and pressurizing at 100-200 ℃ under 1-5 Mpa for reaction for 1-24 h, filtering and drying to obtain a composite material intermediate;

(4) putting the composite material intermediate obtained in the step (3) into an inert atmosphere, and carbonizing at 800-1100 ℃ for 1-12 h to obtain a sulfur-doped pre-lithiated silicon-carbon composite material;

wherein the weight ratio of the organic sulfur compound, the graphene oxide, the organic lithium and the organic solvent is 10: 0.1-1: 1-5: 100.

2. The sulfur-doped prelithiated silicon-carbon composite material produced by the method of claim 1.