Silicon-carbon composite film negative electrode material and preparation method and application thereof

Abstract

The invention discloses a silicon-carbon composite film negative electrode material and a preparation method and application thereof, and belongs to the technical field of lithium ion batteries. The silicon-carbon composite film negative electrode material is of a three-layer film structure and comprises a first silicon-carbon composite film, a second silicon-carbon composite film and a third silicon-carbon composite film which are sequentially stacked, wherein the diameter of the silicon-based material in the second silicon-carbon composite film is greater than the diameters of the silicon-based materials in the first silicon-carbon composite film and the third silicon-carbon composite film; the thickness of the second silicon-carbon composite film is larger than that of the first silicon-carbon composite film and that of the third silicon-carbon composite film. The silicon-carbon composite film negative electrode material has a three-layer structure, and by controlling the diameter and content of the carbon nanoparticles in different layers, on the premise of ensuring the capacity, the silicon nanoparticles can be effectively prevented from being separated from the electrode contact, and the capacity attenuation in the charge-discharge cycle process of the battery is relieved.

Description

Technical Field

[0001] The present invention relates to a technology in the field of lithium-ion batteries, specifically a silicon-carbon composite film negative electrode material and a preparation method and application thereof. Background Art

[0002] The current commercial lithium-ion battery graphite negative electrode has limited its application due to its low theoretical specific capacity (372mAh / g). Silicon is considered to be one of the most promising new negative electrode materials to replace graphite because of its highest theoretical lithium storage capacity (4200mAh / g), moderate voltage platform, abundant resources, low price, and environmental friendliness.

[0003] However, silicon anodes also face several key challenges that severely limit their practical applications. Specifically, on the one hand, the huge volume change of silicon during the charge and discharge process can lead to severe crushing, unstable solid electrolyte interface and loss of electrical contact, limiting the stability and cycle life of the battery; on the other hand, the binder has a great influence on the electrochemical properties of Si / C-based electrodes. The weak van der Waals interaction between most binders and silicon cannot guarantee the integrity of the silicon electrode during the cycle, resulting in loss of electrical contact between silicon particles and peeling of the film from the collector. Therefore, it is not suitable for silicon anodes.

[0004] At present, many methods have been developed to improve the cycle and rate performance of silicon, with the main ideas focusing on silicon nano-sizing, Si / C composite and pre-expansion space. However, the current methods are usually complicated, cumbersome, uncontrollable, low in yield, high in risk, high in cost, and not conducive to mass production.

[0005] In order to solve the above problems in the prior art, the present invention is provided. Summary of the invention

[0006] In view of the above-mentioned deficiencies in the prior art, the present invention proposes a silicon-carbon composite thin film negative electrode material and a preparation method and application thereof, wherein the silicon-carbon composite thin film negative electrode material has a three-layer structure. By controlling the diameter and content of the silicon-based material in different layers, the silicon-based material can be effectively inhibited from being separated from the electrode contact while ensuring the capacity, thereby alleviating the capacity attenuation during the battery charge and discharge cycle.

[0007] The first aspect of the present invention relates to a silicon-carbon composite thin film negative electrode material, which is a three-layer thin film structure, comprising:

[0008] A first silicon-carbon composite film, a second silicon-carbon composite film, and a third silicon-carbon composite film are sequentially stacked;

[0009] The thickness of the first silicon-carbon composite film is 15 to 20 µm, the weight proportion of the silicon-based material is 0.1 to 2 wt%, and the diameter (average particle size) is 0.5 to 10 nm; for example, the thickness of the first silicon-carbon composite film may be 15 µm, 16 µm, 17 µm, 18 µm, 19 µm, 20 µm, etc., the weight proportion of the silicon-based material may be 0.1 wt%, 0.3 wt%, 0.5 wt%, 0.6 wt%, 0.9 wt%, 1.0 wt%, 1.2 wt%, 1.4 wt%, 1.5 wt%, 1.7 wt%, 1.8 wt%, 2.0 wt%, etc., and the diameter of the silicon-based material may be 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, etc.;

[0010] The thickness of the second silicon-carbon composite film is 50-70µm, the weight proportion of the silicon-based material is 25-35wt%, and the diameter is 10-80nm; for example, the thickness of the second silicon-carbon composite film may be 50µm, 55µm, 60µm, 65µm, 70µm, etc., the weight proportion of the silicon-based material may be 25wt%, 26wt%, 27wt%, 28wt%, 29wt%, 30wt%, 31wt%, 32wt%, 33wt%, 34wt%, 35wt%, etc., and the diameter of the silicon-based material may be 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, 55nm, 60nm, 65nm, 70nm, 75nm, 80nm, etc.;

[0011] The thickness of the third silicon-carbon composite film is 15 to 20 µm, the weight proportion of the silicon-based material is 0.1 to 2 wt%, and the diameter is 0.5 to 10 nm; for example, the thickness of the third silicon-carbon composite film may be 15 µm, 16 µm, 17 µm, 18 µm, 19 µm, 20 µm, etc., the weight proportion of the silicon-based material may be 0.1 wt%, 0.3 wt%, 0.5 wt%, 0.6 wt%, 0.9 wt%, 1.0 wt%, 1.2 wt%, 1.4 wt%, 1.5 wt%, 1.7 wt%, 1.8 wt%, 2.0 wt%, etc., and the diameter of the silicon-based material may be 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, etc.;

[0012] Wherein, the diameter of the silicon-based material in the second silicon-carbon composite film is greater than the diameter of the silicon-based material in the first silicon-carbon composite film and the third silicon-carbon composite film;

[0013] The silicon-based material includes silicon nanoparticles and / or nano-SiO x pink.

[0014] For some specific embodiments, the thickness of the first silicon-carbon composite film and the third silicon-carbon composite film, the weight ratio of the silicon-based material and / or the diameter of the silicon-based material may be the same or different.

[0015] For some specific embodiments, the silicon-carbon composite film also includes nanocarbon materials to make up for the poor conductivity of silicon-based materials; the nanocarbon materials include amorphous carbon and / or graphitized carbon, so as to better construct a conductive network in the silicon-carbon composite film and improve the conductivity of the negative electrode material. Preferably, the added weight of the nanocarbon material is less than the added weight of the silicon-based material.

[0016] The second aspect of the present invention relates to a method for preparing a silicon-carbon composite thin film negative electrode material, comprising the following steps:

[0017] S1: Add the silicon-based material and polyoxypropylene-polyoxyethylene copolymer PPO-PEO to N,N-dimethylformamide at 60-70°C, stir for 1-2 hours, and then ultrasonically vibrate to obtain solution A. m ; Dissolve the polymer in N, N-dimethylformamide and mix well to make solution B m ;

[0018] S2: At 60-70°C, add solution A at a mass ratio of 1:2-3 m and B m The mixture was mixed and stirred continuously for 10 to 12 hours using a magnetic stirrer, and then ultrasonically treated for 30 to 40 minutes at room temperature to obtain a homogeneous spinning solution C. m ;

[0019] S3: Electrospinning using a coaxial electrospinning device, homogenizing the spinning solution C m According to the outer tube and inner tube, it is divided into C 外 and C 内 , where the homogeneous spinning solution C in the outer tube 外 Containing 0.1-2wt% silicon-based material with a diameter of 0.5-10nm, the inner tube contains a homogeneous spinning solution C 内 Silicon-based material containing 25 to 35 wt% and a diameter of 10 to 80 nm;

[0020] First, the outer tube homogenous spinning solution is injected, and the injection is stopped after 30 to 40 minutes; then the inner tube homogenous spinning solution is injected, and the injection is stopped after 120 to 150 minutes; then the outer tube homogenous spinning solution is injected again, and the injection is stopped after 30 to 40 minutes, to obtain a three-layer structure nano silicon-carbon fiber film;

[0021] S4: The three-layer structure nano silicon-carbon fiber film is subjected to nitrogen doping treatment to reduce the charge transfer impedance of electrons, improve the electronic conductivity of the material, and improve its rate performance, while increasing the lithium storage capacity to a certain extent; the three-layer structure nano silicon-carbon fiber film obtained in step S3 is dried and preheated in air at 200-300°C for 1-3h, and then kept warm in an inert gas atmosphere containing nitrogen at 650-1100°C for 2-4h to obtain a three-layer structure silicon-carbon composite film negative electrode material.

[0022] For some specific embodiments, step S1 is to prepare solution A. m Nano-carbon materials are added during the process.

[0023] In some specific embodiments, the high molecular weight polymer is polyacrylonitrile, polyvinyl pyrrolidone or polyvinyl alcohol.

[0024] For some specific implementation schemes, the process parameters of the electrospinning are as follows: needle tip voltage is 15 kV, liquid pushing speed is 0.06-0.08 mL / h, spinning distance is 12-15 cm, spinning process humidity is 20%-40%, and spinning process temperature is 20-30°C.

[0025] The third aspect of the present invention relates to the application of the above silicon-carbon composite thin film negative electrode material in lithium-ion batteries.

[0026] Compared with the prior art, the present invention has the following technical effects:

[0027] 1) The above three-layer silicon-carbon composite thin film negative electrode material does not require the addition of a binder during the production process. By controlling the diameter and content of the silicon-based material in different layers, the electrical contact loss caused by the detachment of the silicon-based material can be effectively suppressed while ensuring the capacity, and the capacity attenuation can be alleviated, thus overcoming the problems of large volume changes and easy peeling of silicon particles in the silicon-carbon negative electrode material with the addition of a binder during the charge and discharge cycle.

[0028] 2) The three-layer silicon-carbon composite film negative electrode material is manufactured by electrospinning and applied in battery manufacturing and applications. No current collector is required, which greatly improves the mass specific capacity. The carbon fibers prepared by electrospinning are densely arranged and have small gaps, which can effectively inhibit the expansion of silicon-based materials and increase cycle performance.

[0029] 3) The preparation process is simple, reliable and low-cost; the high molecular polymer as a carbon source is made into solutions with nano-sized silicon-based materials and then mixed, which improves the dispersibility of the silicon-based material and avoids the agglomeration of the silicon-based material during the electrospinning process; and nitrogen is added during the carbonization process for nitrogen doping, which reduces the material impedance and improves the electrochemical performance. DETAILED DESCRIPTION

[0030] The present invention is described in detail below in conjunction with specific embodiments. Experimental methods without specific conditions in the examples are carried out according to conventional methods and conditions.

[0031] Example 1

[0032] The process of making the silicon-carbon composite thin film negative electrode material in this embodiment is as follows.

[0033] Solution preparation

[0034] Silicon nanoparticles with an average particle size of 5 nm and polyoxypropylene-polyoxyethylene copolymer were added to N,N-dimethylformamide, stirred at 60°C for 1 hour, and then ultrasonically treated for 30 minutes to obtain a precursor spinning solution A. 1 ;

[0035] Silicon nanoparticles with an average particle size of 60 nm and polyoxypropylene-polyoxyethylene copolymer were added to N,N-dimethylformamide, stirred at 60°C for 1 hour, and then ultrasonically treated for 30 minutes to obtain a precursor spinning solution A. 2 ;

[0036] 2 g of polyacrylonitrile was dissolved in N,N-dimethylformamide and magnetically stirred for 1 h to obtain a 15 wt % polymer solution B.

[0037] Dispersion and mixing of solutions

[0038] Solution A 1 , A 2 The solution C was mixed with solution B in a mass ratio of 1:2, stirred continuously at 60°C with a magnetic stirrer for 12 h, and then ultrasonically treated at room temperature for 30 min to obtain a homogeneous spinning solution C with a silicon content of 0.12 wt%. 1 and 35wt% silicon content homogeneous spinning solution C 2 .

[0039] Electrospinning

[0040] The homogeneous spinning solution C 1 Add to outer tube, homogenize spinning solution C 2 Add inner tube;

[0041] The positive voltage was set to 15 kV, the negative voltage to 1.5 kV, the ambient temperature to 25 °C, the humidity to 40%, and the high-speed directional accessory was selected as the receiving device; the distance from the nozzle of the coaxial spinning device to the receiving device was 15 cm;

[0042] First, a homogeneous spinning solution C is injected. 1 The liquid pushing speed was 0.06 mL / min, which lasted for 30 min and then stopped; then, the homogeneous spinning solution C was injected. 2The liquid pushing speed is 0.06mL / min, which lasts for 150min and then stops; finally, the homogeneous spinning solution C is pushed again. 1 The liquid pushing speed was 0.06 mL / min, and it was stopped after 30 min. A three-layer nano-silicon-carbon fiber film was obtained.

[0043] Baking Carbonization

[0044] The prepared film was placed in a vacuum drying oven at 60°C and dried for 10 hours. After being completely dried, it was heated to 280°C in air at a heating rate of 2°C / min and preheated for 2 hours. In a nitrogen-argon mixed atmosphere (90:10, V / V), it was heated to 650°C and kept warm for 4 hours to obtain a three-layer silicon-carbon composite thin film negative electrode material.

[0045] Battery Assembly

[0046] The silicon-carbon composite film negative electrode material was cut into 10 mm thin slices using a slicer, and the battery was assembled using a battery packaging machine in an argon atmosphere glove box. The metal lithium sheet was used as the reference electrode, the polypropylene film was used as the battery separator, and the electrolyte was 1.0 mol / L LiPF 6 Solution (the solvent is a mixture of ethylene carbonate and dimethyl carbonate in a volume ratio of 1:1).

[0047] After the battery is assembled, it is left to stand for 48 hours, and the battery is tested for cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) using an electrochemical workstation.

[0048] Example 2

[0049] Compared with Example 1, the difference of this embodiment is that the homogeneous spinning solution C 1 The silicon content is 0.54wt%.

[0050] Example 3

[0051] Compared with Example 1, the difference of this embodiment is that the homogeneous spinning solution C 1 The silicon content is 1.75wt%, homogeneous spinning solution C 2 The silicon content is 30wt%.

[0052] Example 4

[0053] Compared with Example 1, the difference of this embodiment is that the homogeneous spinning solution C 1 The silicon content is 1.32wt%, homogeneous spinning solution C 2 The silicon content is 30wt%.

[0054] Example 5

[0055] Compared with Example 1, the difference of this embodiment is that the homogeneous spinning solution C 1 The silicon content is 1.32wt%, homogeneous spinning solution C 2 The silicon content is 35wt%.

[0056] Example 6

[0057] Compared with Example 1, the difference of this embodiment is that the homogeneous spinning solution C 2 The silicon content is 25wt%.

[0058] Comparative Example 1

[0059] The method for preparing the negative electrode sheet is the same as that in Example 1, except that the precursor spinning solution A 1 and A 2 The average particle size of the silicon nanoparticles added is 60 nm.

[0060] Comparative Example 2

[0061] The method for preparing the negative electrode sheet is the same as that of Comparative Example 1, except that the baking carbonization condition is a hydrogen-argon mixed atmosphere (90:10, V / V).

[0062] Comparative Example 3

[0063] The method for preparing the negative electrode sheet is the same as that of Comparative Example 1, except that the homogeneous spinning solution C 2 The silicon content is 30wt%.

[0064] Comparative Example 4

[0065] The method for preparing the negative electrode sheet is the same as that of Comparative Example 1, except that the homogeneous spinning solution C 2 The silicon content is 25wt%.

[0066] The batteries prepared in Examples 1 to 6 were tested and compared with Comparative Examples 1 to 4. The results are shown in Table 1 below.

[0067] Table 1 Battery performance test table

[0068] It should be emphasized that the above are only preferred embodiments of the present invention and do not limit the present invention in any form. Any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A silicon-carbon composite thin film negative electrode material, characterized in that: It is a three-layer film structure, including: A first silicon-carbon composite film, a second silicon-carbon composite film, and a third silicon-carbon composite film are sequentially stacked; The first silicon-carbon composite film has a thickness of 15 to 20 µm, a weight proportion of the silicon-based material of 0.1 to 2 wt%, and a diameter of 0.5 to 10 nm; The second silicon-carbon composite film has a thickness of 50 to 70 µm, a weight proportion of the silicon-based material of 25 to 35 wt%, and a diameter of 10 to 80 nm; The thickness of the third silicon-carbon composite film is 15 to 20 µm, the weight proportion of the silicon-based material is 0.1 to 2 wt%, and the diameter is 0.5 to 10 nm; Wherein, the diameter of the silicon-based material in the second silicon-carbon composite film is greater than the diameter of the silicon-based material in the first silicon-carbon composite film and the third silicon-carbon composite film; The silicon-based material includes silicon nanoparticles and / or nano-SiO x pink.

2. The silicon-carbon composite thin film negative electrode material according to claim 1, characterized in that: The first silicon-carbon composite film and the third silicon-carbon composite film have the same thickness, weight ratio of silicon-based material and / or diameter of silicon-based material.

3. The silicon-carbon composite thin film negative electrode material according to claim 1, characterized in that: The first silicon-carbon composite film and the third silicon-carbon composite film have different thicknesses, different weight proportions of silicon-based materials, and different diameters of silicon-based materials.

4. The silicon-carbon composite thin film negative electrode material according to claim 1, characterized in that: The first silicon-carbon composite film, the second silicon-carbon composite film and / or the third silicon-carbon composite film are added with nano-carbon materials, and the nano-carbon materials are amorphous carbon and / or graphitized carbon.

5. A method for preparing the silicon-carbon composite thin film negative electrode material according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1: Add the silicon-based material and polyoxypropylene-polyoxyethylene copolymer PPO-PEO to N,N-dimethylformamide at 60-70°C, stir for 1-2 hours, and then ultrasonically vibrate to obtain solution A. m ; Dissolve the polymer in N, N-dimethylformamide and mix well to make solution B m ; S2: At 60-70°C, add solution A at a mass ratio of 1:2-3 m and B m The mixture was mixed and stirred continuously for 10 to 12 hours using a magnetic stirrer, and then ultrasonically treated for 30 to 40 minutes at room temperature to obtain a homogeneous spinning solution C. m ; S3: Electrospinning using a coaxial electrospinning device, homogenizing the spinning solution C m According to the outer tube and inner tube, it is divided into C 外 and C 内 , where the homogeneous spinning solution C in the outer tube 外 Containing 0.1-2wt% silicon-based material with a diameter of 0.5-10nm, the inner tube contains a homogeneous spinning solution C 内 Silicon-based material containing 25 to 35 wt% and a diameter of 10 to 80 nm; First, the outer tube homogenous spinning solution is injected, and the injection is stopped after 30 to 40 minutes; then the inner tube homogenous spinning solution is injected, and the injection is stopped after 120 to 150 minutes; then the outer tube homogenous spinning solution is injected again, and the injection is stopped after 30 to 40 minutes, to obtain a three-layer structure nano silicon-carbon fiber film; S4: nitrogen doping the three-layer structure nano silicon-carbon fiber film; drying the three-layer structure nano silicon-carbon fiber film obtained in step S3, preheating it in air at 200-300°C for 1-3h, and then keeping it in an inert gas atmosphere containing nitrogen at 650-1100°C for 2-4h to obtain a three-layer structure silicon-carbon composite film negative electrode material.

6. The preparation method according to claim 5, characterized in that: The high molecular polymer is polyacrylonitrile, polyvinyl pyrrolidone or polyvinyl alcohol.

7. The preparation method according to claim 5, characterized in that: The process parameters of the electrospinning are as follows: needle tip voltage is 15 kV, liquid pushing speed is 0.06-0.08 mL / h, spinning distance is 12-15 cm, spinning process humidity is 20%-40%, and spinning process temperature is 20-30° C.

8. The preparation method according to claim 5, characterized in that: In step S1, solution A is prepared m Nano-carbon materials are added during the process.

9. Use of the silicon-carbon composite thin film negative electrode material according to any one of claims 1 to 4 in a lithium ion battery.

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