Metal-organic framework coated modified silicon-carbon negative electrode material, and preparation method and application thereof

Abstract

The application belongs to the technical field of lithium ion battery negative electrode material, and provides metal organic framework coated modified silicon-carbon negative electrode material, a preparation method and application thereof, and comprises the following steps: dispersing silicon-carbon powder in ethanol, ultrasonic treatment, adding trimesic acid and Ni(NO3)2.6H2O, stirring, heating for reaction, cooling to room temperature, centrifugal separation of the product, washing, vacuum drying of the obtained washing product, and obtaining Si@C-Ni-MOF; adding super p, Si@C-Ni-MOF and CMC into deionized water, oscillating and mixing uniformly, adding SBR and mixing uniformly, adding deionized water and mixing uniformly, drying and defoaming, adding dropwise on the surface of copper foil after stirring, coating, drying the coated copper foil, and obtaining metal organic framework coated modified silicon-carbon negative electrode material. The application improves the electrochemical performance of the negative electrode material, and can realize high initial efficiency and excellent cycle performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion battery negative electrode materials, and particularly relates to a metal organic framework coated modified silicon-carbon negative electrode material and a preparation method and application thereof. BACKGROUND

[0002] Lithium ion batteries are widely concerned due to their high energy density, long service life, low discharge rate and other advantages, wherein the negative electrode material of the lithium ion battery is one of the key factors restricting its performance. The currently commercialized graphite negative electrode material has a low theoretical capacity (372 mAh g -1 ), which limits the further improvement of the performance of the lithium ion battery. The silicon-based material has a theoretical capacity as high as 3579 mAh g -1 , a stable working voltage, and is abundant in reserves and low in price, and is the most promising negative electrode material for a new generation of lithium ion batteries, but its practical application is faced with serious problems such as volume expansion and pulverization, low first coulomb efficiency, low intrinsic electronic conductivity, slow lithium ion diffusion and unstable solid electrolyte interface.

[0003] In view of the inherent problems of the silicon-based negative electrode, various strategies have been developed: nano-structuring of silicon: reducing the size of silicon to the nanoscale to form nanoparticles, nanowires and nanosheets, which can alleviate the volume expansion and contraction adaptability during the lithium intercalation / deintercalation process, thereby reducing mechanical stress and reducing the risk of cracking and pulverization; composite material design: silicon-carbon and silicon-graphene composite materials can improve the electrical conductivity, structural integrity and mechanical buffering capacity, effectively alleviate the volume change problem and optimize the overall electrochemical performance; surface coating: a protective outer layer of carbon layer, inorganic material and conductive polymer can adapt to the size change of silicon, maintain structural integrity and electrical conductivity; innovative binder and electrolyte engineering technology: conductive, self-repairing and ion-conducting binders, in cooperation with new electrolytes and additives, significantly improve the mechanical toughness, SEI stability and cycle performance of the silicon-based negative electrode; pre-lithiation technology: various pre-lithiation methods such as chemical, electrochemical and mechanical methods are established to solve the problem of initial irreversible capacity loss and improve the initial coulomb efficiency (CE) of the silicon-based negative electrode.

[0004] Among them, the current mainstream technology is to combine the silicon negative electrode material with the carbon material, mainly because the carbon material has a small volume change during charging and discharging, has good cycle stability, and has good electrical conductivity; in the silicon-carbon composite system, silicon serves as the active material to provide lithium storage capacity, and the carbon material not only alleviates the serious volume expansion of the silicon negative electrode during charging and discharging, but also improves the electrical conductivity and avoids silicon agglomeration to maintain a stable SEI layer. Therefore, the silicon-carbon composite material combines the advantages of both and exhibits high specific capacity and long cycle life.

[0005] Although the inherent problems of silicon-based negative electrodes are solved to some extent by the above method, the commercialization of silicon-based negative electrodes still faces many obstacles, such as the cycle stability and electrochemical performance of silicon-carbon negative electrode materials still need to be further improved, and the large-scale production process still needs to be optimized, etc. Therefore, it is of great significance to use more innovative technologies for structural design, explore more delicate and ingenious structures, and further improve the cycle performance and service life. SUMMARY

[0006] The purpose of the embodiment of the present application is to provide a preparation method of metal organic framework coated modified silicon-carbon negative electrode material, aiming to solve the problems raised in the above background.

[0007] The embodiment of the present application is implemented in this way, the preparation method of metal organic framework coated modified silicon-carbon negative electrode material, comprising the following steps:

[0008] Preparation of Si@C-Ni-MOF: disperse silicon-carbon powder in ethanol, ultrasonic treatment, then add trimesic acid and Ni(NO3)2·6H2O, stir, heat for reaction, then cool to room temperature, centrifugal separation of the product, washing, vacuum drying of the obtained washed product, to obtain Si@C-Ni-MOF;

[0009] Si@C-Ni-MOF negative electrode material coating: add super p (conductive carbon black), Si@C-Ni-MOF and CMC (binder carboxymethyl cellulose sodium) into deionized water, oscillate and mix uniformly, add SBR (styrene-butadiene rubber) and mix uniformly, add deionized water and mix uniformly, then dry and defoam, then drop on the surface of copper foil after stirring, coat, then dry the coated copper foil, to obtain metal organic framework coated modified silicon-carbon negative electrode material.

[0010] Another purpose of the embodiment of the present application is to provide a metal organic framework coated modified silicon-carbon negative electrode material, which is prepared by the above preparation method.

[0011] Another purpose of the embodiment of the present application is to provide a metal organic framework coated modified silicon-carbon negative electrode material in the preparation of lithium ion batteries.

[0012] The embodiment of the present application adopts a hydrothermal synthesis method to synthesize metal organic framework coated silicon-carbon negative electrode material, the network layer constructed by the metal organic framework provides skeleton support and buffer space for the volume shrinkage and expansion effect of silicon in the charging and discharging process, and also ensures the high-speed passage of electrons; at the same time, a large number of metal open sites on the structure skeleton are beneficial to the fixation of anions, so as to realize faster lithium ion migration and uniform lithium deposition, and inhibit the growth of lithium dendrites, which provides protection for the stable operation of the subsequent battery.

[0013] The metal organic framework coated silicon-carbon negative electrode prepared by the embodiment of the present application can be applied to a lithium ion battery. Thanks to the ability of the metal organic framework to relieve the volume expansion of silicon and the faster lithium ion transmission ability, the electrochemical performance of the negative electrode material is improved, and high initial efficiency and excellent cycle performance can be achieved. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 SEM image of Si@C-Ni-MOF synthesized in Example 1 of the present application;

[0015] Figure 2 TEM image of Si@C-Ni-MOF synthesized in Example 1 of the present application;

[0016] Figure 3 FT-IR image of Si@C-Ni-MOF synthesized in Example 1 of the present application;

[0017] Figure 4 XRD image of Si@C-Ni-MOF synthesized in Example 1 of the present application;

[0018] Figure 5 SEM image of Si@C-Ni-MOF electrode sheet obtained in Example 2 of the present application;

[0019] Figure 6 Cycle performance of the lithium ion battery assembled by using the original silicon-carbon negative electrode material in Comparative Example 1 of the present application;

[0020] Figure 7 Cycle performance of the lithium ion battery assembled by using the metal organic framework coated silicon-carbon negative electrode material in Example 3 of the present application. DETAILED DESCRIPTION

[0021] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application.

[0022] The silicon-carbon powder used in the embodiment of the present application is a commercial silicon-carbon provided by the Carbon New Energy Group Co., Ltd., and the model number is C ONE-SC 1800.

[0023] The specific implementation of the present application will be described in detail below in combination with specific examples.

[0024] Example 1, Si@C-Ni-MOF, the synthesis of which includes the following steps:

[0025] (1) Disperse 100 mg of silicon-carbon powder in 50 mL of ethanol and ultrasonic for 30 min;

[0026] (2) 22.5 mg of trimesic acid and 22.5 mg of Ni(NO3)2·6H2O were added to the solution obtained in step (1);

[0027] (3) The mixed solution obtained in step (2) was transferred to a reaction kettle, and reacted at 150 °C for 15 h under an oven;

[0028] (4) The solution obtained in step (3) was cooled to room temperature, and the product was separated by centrifugation and washed with ethanol three times;

[0029] (5) The washed product obtained in step (4) was placed in a vacuum drying oven at 55 °C to obtain the final product, denoted as Si@C-Ni-MOF.

[0030] The Si@C-Ni-MOF prepared in Example 1 was characterized by scanning electron microscopy, transmission electron microscopy, infrared spectroscopy, and XRD, and the results are shown in Figures 1-4 ; Figure 1 and Figure 2 are SEM and TEM images of Si@C-Ni-MOF, and from the images it can be clearly seen that the Ni-MOF is successfully coated on the surface of the silicon-carbon negative electrode, Figure 3 is the FT-IR spectrum of Si@C-Ni-MOF, and the appearance of the characteristic absorption peak at 726 cm -1 corresponding to the stretching vibration of Ni-O indicates the successful synthesis of the sample, Figure 4 is the XRD pattern of Si@C-Ni-MOF, and the appearance of the characteristic diffraction peak of Ni-MOF in the range of 5-20° further proves the above results.

[0031] Example 2, Si@C-Ni-MOF negative electrode material coating, the specific steps are as follows:

[0032] (1) 625 μL of deionized water was added to a centrifuge tube containing 450 mg of Si@C-Ni-MOF prepared in Example 1, 25 mg of super p, and 18.75 mg of CMC, 5 smallest ball milling beads (stirring effect), and mixed uniformly with a homogenizer at a speed of 400 rpm; then 70 μL of SBR was added and mixed at a speed of 200 rpm for 30 min; then 625 μL of deionized water was added and mixed at a speed of 300 rpm for 30 min;

[0033] (2) The centrifuge tube was placed in a vacuum drying oven and dried for 1 min, then stirred appropriately, and dropped onto the surface of a copper foil with a dropper, and coated with a spatula;

[0034] (3) The coated copper foil was placed in a 60 °C oven to dry, obtaining a Si@C-Ni-MOF electrode sheet (metal-organic framework coated silicon-carbon negative electrode material).

[0035] The electrode sheet prepared in Example 2 was characterized by scanning electron microscopy, and the results are shown in Figure 5 , Figure 5 It can be seen that the surface of the Si-C negative electrode is covered by Ni-MOF nanosheets. This porous structure composed of Ni-MOF nanosheets not only facilitates the transmission of lithium ions, but also provides sufficient space to relieve the volume expansion of silicon during the cycle process.

[0036] Example 3, a method for manufacturing a lithium ion battery, comprising the following steps:

[0037] In the glove box, the Si@C-Ni-MOF electrode sheet prepared in Example 2, the electrolyte (the electrolyte is a 1 M LiPF6 (lithium hexafluorophosphate) electrolyte purchased from the Multitester Network, and the volume ratio of EC (ethylene carbonate) and DEC (diethyl carbonate) is 1:1. The finished electrolyte is added with 5% FEC (fluorinated ethylene carbonate) by mass fraction), NCM811 positive electrode are placed on the 2032 negative electrode shell in turn, and finally the 2032 positive electrode shell is capped and assembled. The battery is placed on the battery packaging machine and packaged under a pressure of 50 kg / cm -2 to obtain a lithium ion battery.

[0038] Comparative Example 1, compared with Example 3, the only difference is that the Si@C-Ni-MOF electrode sheet prepared in Example 2 is adjusted to a commercial silicon-carbon negative electrode material.

[0039] The lithium ion batteries prepared in Comparative Example 1 and Example 3 were respectively subjected to cycle performance test, and the results are shown in Figure 6 , Figure 7 As can be seen from the comparison of the two figures, the battery assembled by the Si@C-Ni-MOF electrode sheet has a higher initial efficiency, and after 50 cycles, the capacity attenuation is weak. The Ni-MOF framework greatly improves the cycle performance of Si@C-Ni-MOF, and makes the battery exhibit better cycle stability.

[0040] The above only describes the preferred embodiments of the present application and should not be used to limit the present application. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A method for preparing metal-organic framework-coated modified silicon-carbon anode materials, characterized in that, include: Preparation of Si@C-Ni-MOF: Silicon carbon powder was dispersed in ethanol, ultrasonically treated, and then pyromellitic acid and Ni(NO3)2·6H2O were added. The mixture was stirred, heated to react, cooled to room temperature, centrifuged to separate the product, washed, and the washed product was vacuum dried to obtain Si@C-Ni-MOF. The mass ratio of pyromellitic acid to Ni(NO3)2·6H2O was 1:

1. Si@C-Ni-MOF anode material coating: Si@C-Ni-MOF, super p, and CMC were added to deionized water and shaken to mix. SBR was added and mixed, followed by deionized water and mixed again. The mixture was then dried and defoamed. After stirring, the mixture was dropped onto the surface of copper foil for coating. The coated copper foil was then dried to obtain the metal-organic framework-coated modified silicon-carbon anode material. The shaking and mixing speed was 400 rpm, the SBR was added and mixed at 200 rpm, and the deionized water was added and mixed at 300 rpm.

2. The method for preparing the metal-organic framework-coated modified silicon-carbon anode material according to claim 1, characterized in that, In the Si@C-Ni-MOF anode material coating step, the mass ratio of Si@C-Ni-MOF, super p, and CMC is 90:5:3.

75.

3. A metal-organic framework-coated modified silicon-carbon anode material, characterized in that, It is prepared using the preparation method described in any one of claims 1-2.

4. The application of the metal-organic framework-coated modified silicon-carbon anode material as described in claim 3 in the preparation of lithium-ion batteries.

5. The application according to claim 4, characterized in that, Includes the following steps: The metal-organic framework-coated modified silicon-carbon anode material, electrolyte, and NCM811 cathode are sequentially placed on the anode shell, and finally the cathode shell is covered and assembled. The battery is placed on a battery packaging machine and packaged under pressure to obtain a lithium-ion battery.

6. The application according to claim 5, characterized in that, The electrolyte is LiPF6, EC, DEC, and FEC.

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