Lithium ion battery silicon-carbon composite negative electrode material and preparation method and application thereof

Abstract

The application belongs to the technical field of lithium ion batteries, and particularly relates to a silicon-carbon composite material, a preparation method thereof and application of the silicon-carbon composite material as a negative electrode material of a lithium ion battery. The silicon-carbon composite material is obtained by sequentially depositing nano-silicon through pyrolysis of a silicon source gas and coating carbon through pyrolysis of a carbon source gas from cross-linked porous hard carbon, and the cross-linked porous hard carbon is obtained by carbonizing starch and resin together and then activating the carbonized product by an activating agent. The starch-resin cross-linked composite porous hard carbon has better mechanical strength than starch porous hard carbon and resin porous hard carbon, and can better adapt to the stress generated by the volume change of silicon particles in the charging and discharging process, so that the gas-phase deposited silicon-carbon composite material has better electrochemical performance when used as a negative electrode of a lithium ion battery. The raw materials involved in the application are easy to obtain, the preparation method is simple and easy to implement, the production can be easily scaled up, the cost is lower than that of the currently commonly used resin-based hard carbon material, and the application has great development and application potential.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to silicon-carbon composite materials, their preparation methods, and their application as negative electrode materials for lithium-ion batteries. Background Technology

[0002] Lithium-ion batteries are widely used in various fields of human society due to their advantages such as high energy density, long cycle life, no memory effect, and low self-discharge. In recent years, the rapid development of electric vehicles, hybrid vehicles, and energy storage devices has placed higher demands on the specific energy density and power density of lithium-ion batteries. Currently, the specific energy density of lithium-ion batteries with graphite anodes as the mainstream is approaching its theoretical limit, and there is an urgent need to develop a new generation of electrode materials with high specific energy density. Silicon-based anode materials have a theoretical specific capacity as high as 4200 mAh / g, and with low operating potential, abundant natural reserves, and environmental friendliness, they have attracted widespread attention and are considered one of the important choices for lithium-ion battery anode materials.

[0003] However, silicon undergoes a volume change of approximately 300% during charge and discharge, leading to numerous adverse effects such as Si particle fragmentation during charge-discharge cycles, detachment of active material from the current collector, and repeated growth of the solid electrolyte interphase (SEI) film. Furthermore, Si's poor electrical conductivity is another disadvantage as an electrode active material. Currently, many research strategies have been proposed to overcome the problems of silicon-based anodes, such as nano-sizing of Si, designing suitable structures, developing novel binders, and composite formation with carbon. Among these, the preparation of silicon-carbon composite materials through carbon composite formation is currently the most promising method.

[0004] Among the numerous solutions to the volume expansion problem of silicon-based materials, three routes have been industrialized. The first is the grinding method for preparing nano-silicon-carbon, the second is the carbon-coated silicon-oxygen route, and the third is the CVD (chemical vapor deposition) silicon-carbon route. Among these, the CVD silicon-carbon route is considered the most promising. One of the most crucial issues for CVD silicon-carbon materials is the selection of the carbon matrix. The mechanical strength, pore volume, and porosity of the carbon matrix have a significant impact on the final performance of the CVD silicon-carbon material. Therefore, it is essential to prepare a porous carbon material with a suitable pore structure and sufficient mechanical strength as the carbon matrix for CVD silicon-carbon materials. Summary of the Invention

[0005] The purpose of this invention is to provide a low-cost, high-performance, mass-producible silicon-carbon composite anode material for lithium-ion batteries, its preparation method, and its application.

[0006] The silicon-carbon composite material provided by this invention is obtained by sequentially depositing nano-silicon through silicon source gas pyrolysis and carbon coating through carbon source gas pyrolysis of cross-linked porous hard carbon. The cross-linked porous hard carbon is obtained by carbonizing a mixture of starch and resin and then activating it with an activator. The specific steps are as follows:

[0007] (1) Weigh starch and resin powder with a mass ratio between 10:1 and 1:10 and transfer them to a mortar. After grinding and mixing, transfer them to a porcelain boat.

[0008] (2) Place the ceramic boat from step (1) into a tube furnace and heat it in an inert gas atmosphere. Set the heating rate to 1-10℃ / min and heat it to 500-1600℃. Hold it for 0.5-5h and then let it cool naturally to obtain cross-linked hard carbon material.

[0009] (3) Transfer the cross-linked hard carbon material obtained in step (2) into a beaker, add an activator, the mass of which is 1-10 times the mass of the cross-linked hard carbon, then add deionized water and stir evenly. After standing for 1-5 hours, put the beaker into an 80-180℃ forced-air drying oven and dry for 5-50 hours until the water in the solution is dried.

[0010] (4) Transfer the dried material from step (3) into a ceramic boat and place it in a tube furnace. Heat it in an inert gas atmosphere, set the heating rate to 1-10℃ / min, heat it to 600-1500℃ and hold it for 0.5-5h, then let it cool naturally to obtain porous cross-linked hard carbon material.

[0011] (5) Place the porous cross-linked hard carbon material obtained in step (4) in a beaker, add hydrochloric acid to wash until the pH is acidic, then add deionized water to filter and wash until the pH is neutral; place the washed porous cross-linked hard carbon material in an 80-180℃ forced-air drying oven to dry;

[0012] (6) Place the porous cross-linked hard carbon material obtained in step (5) in a deposition equipment, heat it to 300-600℃ at 1-10℃ / min in an inert gas atmosphere, introduce a silicon source gas mixture and keep it at the temperature for 1-10h. After deposition, heat it to 600-1000℃ at 1-10℃ / min in an Ar atmosphere, introduce a carbon source gas and keep it at the temperature for 0.1-5h, and then cool it to room temperature in an inert gas atmosphere to obtain silicon-carbon composite anode material.

[0013] In step (3), the activator is one or more of KOH, NaOH, ZnCl2, and H3PO4.

[0014] In steps (2), (4), and (6), the inert gas is one or more of Ar, N2, and He.

[0015] In step (6), the silicon source gas is one or more of the following: silane, silane, chlorosilane, etc., which can be decomposed into silicon atoms.

[0016] In step (6), the carbon source gas is one or more alkanes that can be cracked into carbon at 600 to 1000°C.

[0017] In step (6), the deposition equipment is any one of rotary tube furnace, rotary kiln, fixed bed, and fluidized bed.

[0018] In this invention, the hard carbon matrix is ​​obtained by cross-linking and carbonizing starch and resin.

[0019] In this invention, the porous cross-linked hard carbon matrix is ​​obtained by mixing a solution of pre-carbonized products and activators, drying, and activating at high temperature.

[0020] The silicon-carbon composite material prepared by this invention can be used as a negative electrode material for lithium-ion batteries.

[0021] The starch-resin crosslinked porous hard carbon matrix proposed in this invention has a lower cost than resin-based porous hard carbon, a simpler process, and higher scalability. Silicon-carbon composite materials prepared using this matrix exhibit high specific capacity, good cycle stability, and low electrode expansion rate. Therefore, the starch-resin crosslinked porous hard carbon matrix and the silicon-carbon composite anode materials prepared using it as a matrix described in this invention have lower costs and great development potential. Attached Figure Description

[0022] Figure 1 These are thermogravimetric diagrams of the phenolic resin, corn starch, and carbonized mixtures of the two in different mass ratios used in the examples and comparative examples.

[0023] Figure 2 This is a SEM image of the negative electrode material obtained in Example 1.

[0024] Figure 3 These are the first charge-discharge curves of the batteries assembled from the negative electrode materials obtained in Examples 1, 2, and 1.

[0025] Figure 4 These are charge-discharge cycle performance diagrams of batteries assembled from the negative electrode materials obtained in Examples 1, 2, and 1. Detailed Implementation

[0026] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0027] Example 1: Preparation of a silicon-carbon composite material, the specific steps are as follows:

[0028] S1: Weigh corn starch and phenolic resin powder in a 1:1 mass ratio, transfer them to a mortar, grind and mix them, and then transfer them to a porcelain boat.

[0029] S2: Place the ceramic boat from step S1 into a tube furnace, introduce Ar gas and heat it. Set the heating rate to 1-10℃ / min, heat it to 500-1000℃ and hold it for 0.5-5 hours, then let it cool naturally to obtain cross-linked hard carbon material.

[0030] S3: Transfer the cross-linked hard carbon material obtained in step S2 into a beaker, add 1-10 times the mass of potassium hydroxide (KOH) of the cross-linked hard carbon material, add an appropriate amount of deionized water and stir evenly. After standing for 1-5 hours, put the beaker into a 120℃ forced-air drying oven and dry for 5-50 hours.

[0031] S4: Transfer the dried material from step S3 to a ceramic boat and place it in a tube furnace. Introduce Ar gas and heat it. Set the heating rate to 1-10℃ / min. Heat to 600-1000℃ and hold for 0.5-5 hours. Then allow it to cool naturally to obtain porous cross-linked hard carbon material.

[0032] S5: Place the porous cross-linked hard carbon material obtained in step S4 in a beaker, add hydrochloric acid to wash until the pH is acidic, then add deionized water and filter to wash until the pH is neutral. Place the washed porous cross-linked hard carbon material in a 120℃ forced-air drying oven and dry overnight.

[0033] S6: Place the porous cross-linked hard carbon material obtained in step S5 in a rotary deposition tube furnace, heat it to 300-600℃ at 1-10℃ / min under Ar atmosphere, introduce a SiH4:Ar=95:5 mixed gas and keep it at this temperature for 1-10h. After deposition, heat it to 600-1000℃ at 1-10℃ / min under Ar atmosphere, introduce C2H2 gas and keep it at this temperature for 0.1-5h, and then cool it to room temperature under Ar atmosphere to obtain silicon-carbon composite anode material.

[0034] The thermogravimetric analysis (TGA) of the phenolic resin, corn starch, and the carbonization of the two mixed in different mass ratios used in Example 1 is shown below. Figure 1 SEM images of the prepared anode material are shown below. Figure 2 .

[0035] Figure 3 This is a graph showing the first charge-discharge curve of the battery assembled with the negative electrode materials obtained in Example 1 and Comparative Example 1. Example

[0036] The preparation steps are basically the same as in Example 1, except that step S1 is changed to weighing corn starch and phenolic resin powder in a mass ratio of 2:1 in a ceramic boat.

[0037] Comparative Example 1

[0038] The preparation steps are basically the same as in Example 1, except that step S1 is replaced by weighing pure phenolic resin powder in a ceramic boat.

[0039] The negative electrode materials prepared in the examples and comparative examples were used to assemble batteries. The batteries were subjected to constant current charge-discharge tests on a Blue Electric testing system, with the test current set at 500 mA / g and the test voltage range of 0.005-2V.

[0040] The first charge-discharge curves of the batteries assembled with the negative electrode materials obtained in Examples 1, 2, and 1 are shown below. Figure 3 .

[0041] The charge-discharge cycle performance diagrams of the batteries assembled with the negative electrode materials obtained in Examples 1, 2, and 1 are shown below. Figure 4 .

Claims

1. A method for producing a silicon-carbon composite material, characterized by, The silicon-carbon composite material is obtained by sequentially depositing nano-silicon by pyrolysis of silicon source gas and carbon-coating by pyrolysis of carbon source gas from the cross-linked porous hard carbon, and the cross-linked porous hard carbon is obtained by carbonizing starch and resin together and then activating with an activating agent, and the specific steps are as follows: (1) The starch and phenolic resin powder with a mass ratio of 10:1 to 1:10 are weighed and transferred into a mortar, and after grinding and mixing, they are transferred into a porcelain boat; (2) The porcelain boat in step (1) is placed in a tube furnace and heated in an inert gas atmosphere, the heating rate is set to 1-10℃ / min, heated to 500-1600℃ and kept for 0.5-5h, and then naturally cooled to obtain cross-linked hard carbon material; (3) The cross-linked hard carbon material obtained in step (2) is transferred into a beaker, an activating agent is added, the mass of the activating agent is 1-10 times the mass of the cross-linked hard carbon, deionized water is added and stirred uniformly, and after standing for 1-5h, the beaker is placed in a 80-180℃ air drying oven and dried for 5-50h until the water in the solution is dried; (4) The dried material in step (3) is transferred to a porcelain boat and placed in a tube furnace and heated in an inert gas atmosphere, the heating rate is set to 1-10℃ / min, heated to 600-1500℃ and kept for 0.5-5h, and then naturally cooled to obtain a porous cross-linked hard carbon material; (5) The porous cross-linked hard carbon material obtained in step (4) is placed in a beaker, washed with hydrochloric acid until the pH is acidic, and then washed with deionized water until the pH is neutral; The washed porous cross-linked hard carbon material is dried in an 80-180℃ air drying oven; (6) The porous cross-linked hard carbon material obtained in step (5) is placed in a deposition device, heated to 300-600℃ at a rate of 1-10℃ / min in an inert gas atmosphere, and silicon source gas mixture is introduced and kept for 1-10h, after deposition, heated to 600-1000℃ at a rate of 1-10℃ / min in Ar atmosphere, and carbon source gas is introduced and kept for 0.1-5h, and then cooled to room temperature in an inert gas atmosphere to obtain a silicon-carbon composite material.

2. The production method according to claim 1, characterized by, The activating agent in step (3) is one or more of KOH, NaOH, ZnCl2, and H3PO4.

3. The preparation method according to claim 1, characterized in that, The inert gas in steps (2), (4), and (6) is one or more of Ar, N2, and He.

4. The method of claim 1, wherein, The silicon source gas in step (6) is one or more of methylsilane, ethylsilane, and chlorosilane.

5. The preparation method according to claim 1, characterized in that, The carbon source gas in step (6) is one or more of alkanes that can be cracked into carbon at 600-1000℃.

6. The method of claim 1, wherein, The deposition device in step (6) is any one of a rotary tube furnace, a rotary kiln, a fixed bed, and a fluidized bed.

7. A silicon-carbon composite material prepared by the method of claim 1.

8. Use of the silicon-carbon composite material of claim 7 as a negative electrode material for lithium ion batteries.

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