Composite silicon-based negative electrode material, preparation method thereof and battery

Abstract

The invention belongs to the technical field of battery materials, and discloses a composite silicon-based negative electrode material, a preparation method thereof and a battery, the composite silicon-based negative electrode material comprises nanometer silicon and a carbon net, the nanometer silicon is distributed on the carbon net, and the nanometer silicon and the carbon net are tightly combined; the carbon net is doped with a nitrogen element, and the surface of the carbon net is loaded with nano-copper. The carbon material is doped into the silicon-based negative electrode material, the copper nanodots in the carbon material can promote electron conduction, and the nitrogen-doped carbon net has higher stability and can provide better frame support for the copper nanodots and nano silicon, so that the structural stability and conductivity of the silicon-based negative electrode material are improved, and the volume change of the silicon-based negative electrode material is relieved. Besides, the nitrogen-doped carbon net loaded with the copper nanodots provides a stable composite layer for the nano silicon material, so that the volume expansion of the silicon negative electrode can be effectively inhibited, and the structural stability of the silicon negative electrode is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of battery materials, and relates to a negative electrode material, in particular to a composite silicon-based negative electrode material and a preparation method thereof and a battery. BACKGROUND

[0002] With the continuous development of lithium ion battery technology, the development of high specific energy lithium ion batteries has become an unstoppable trend. In order to improve the specific energy of lithium ion batteries, it is necessary to proceed from two aspects of lithium ion battery structure design and new material development. The main method of battery structure design is to reduce the weight of structural parts, copper foil, aluminum foil and other non-active materials, thereby increasing the proportion of active materials and improving the specific energy of lithium ion batteries. The main method of new material development is to develop positive and negative electrode materials with higher capacity, and positive electrode materials with higher voltage, so as to improve the capacity and voltage of the battery and achieve the purpose of improving the energy density of the battery.

[0003] At present, the development direction of negative electrode materials is mainly to improve the capacity of the materials. For example, the capacity of the Si-based material which is now a relatively mature technology can reach more than 1000 mAh / g, which is much higher than that of graphite materials.

[0004] However, the silicon-based negative electrode material also has a serious volume expansion problem. In the fully embedded lithium state, the volume expansion of the Si negative electrode can reach 300%, which not only causes the particles of the Si negative electrode to break, but also damages the conductive network and the adhesive network of the electrode, resulting in loss of active materials, thereby seriously affecting the cycle performance of the silicon-based negative electrode material, which has become the main obstacle to the application of Si negative electrode materials. SUMMARY

[0005] In view of the defects and deficiencies of the prior art, in a first aspect, the application provides a composite silicon-based negative electrode material; in a second aspect, the application provides a preparation method of the composite silicon-based negative electrode material; and in a third aspect, the application provides a battery.

[0006] In a first aspect, the application provides a composite silicon-based negative electrode material, which comprises nano-silicon and a carbon network, the nano-silicon is distributed on the carbon network, and the nano-silicon and the carbon network are tightly combined; the carbon network is doped with nitrogen elements, and the surface of the carbon network is loaded with nano-copper.

[0007] Preferably, the size of the nano-silicon is 50-100 nm.

[0008] In a second aspect, the application provides a preparation method of the composite silicon-based negative electrode material, which comprises: mixing a copper-based nitrogen heterocyclic crown ether complex and nano-silicon, and sintering under a protective atmosphere to obtain the composite silicon-based negative electrode material.

[0009] Preferably, the mass ratio of the copper-based nitrogen heterocyclic crown ether complex to the nano-silicon is (0.1-0.8) : 1.

[0010] Preferably, the sintering temperature is 500-700℃, and the sintering time is 5-10h.

[0011] Preferably, the preparation method of the copper-based azacrown ether complex comprises mixing azacrown ether, copper salt and water, centrifuging, water washing and drying after coordination reaction for a certain time.

[0012] Preferably, the azacrown ether is any one or two or more of pyridine-azacrown ether, azac-18-crown-6, 4,13-diaz-18-crown-6-ether, azac-15-crown-5.

[0013] Preferably, the copper salt is any one or two or more of copper sulfate, copper chloride and copper nitrate.

[0014] Preferably, the molar ratio of azacrown ether to copper salt is (5-10) : 1.

[0015] Preferably, the coordination reaction time is 10-20h.

[0016] Preferably, the gas for providing the protective atmosphere is any one or two of nitrogen or argon.

[0017] In a third aspect, the present application provides a battery comprising the composite silicon-based negative electrode material.

[0018] Compared with the prior art, the present application has the following obvious beneficial effects: (1) The present application incorporates carbon material into the silicon-based negative electrode material, and the copper nanodots in the carbon material can promote electron conduction. The nitrogen-doped carbon network loaded with copper nanodots provides a stable composite layer for the nanosilicon material, which can effectively inhibit the volume expansion of the silicon negative electrode and improve the structural stability of the silicon negative electrode.

[0019] (2) The composite silicon-based negative electrode material is obtained by sintering the copper-based azacrown ether complex and nanosilicon, and the preparation process is simple and easy to realize large-scale production, which is conducive to commercialization and marketization. The silicon-based negative electrode material exhibits excellent cycle reversibility and structural stability. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 SEM image of the composite silicon negative electrode material prepared in Example 1; Figure 2 EDS image of the composite silicon negative electrode material prepared in Example 1; Figure 3 Cycle performance test chart of the battery assembled with the silicon negative electrode materials prepared in Examples 1-3 and Comparative Examples 1-3 and nanosilicon; Figure 4SEM image of the electrode sheet prepared from the composite silicon negative electrode material prepared in Example 1 after 50 cycles; Figure 5 SEM image of the electrode sheet prepared from the composite silicon negative electrode material prepared in Comparative Example 1 after 50 cycles; Figure 6 SEM image of the electrode sheet prepared from the nano-silicon after 50 cycles. DETAILED DESCRIPTION

[0021] The present application provides the following specific technical solutions.

[0022] In a first aspect, the present application provides a composite silicon-based negative electrode material, comprising nano-silicon and a carbon network, wherein the nano-silicon is distributed on the carbon network, and the nano-silicon and the carbon network are tightly combined; the carbon network is doped with nitrogen elements, and the surface of the carbon network is loaded with nano-copper.

[0023] The inventors have found that the carbon network has good flexibility and elasticity, and as a skeleton structure, the carbon network supports the silicon particles to form a stable overall electrode structure, reduces the displacement and agglomeration of the silicon particles during the charging and discharging process, ensures the structural stability of the electrode, can buffer the volume expansion and contraction of the silicon during the charging and discharging process, and reduces the pulverization of the silicon particles. The carbon network has a large specific surface area and rich pore structure, can better adsorb the electrolyte, promotes the uniform distribution of the electrolyte in the electrode, and thus accelerates the diffusion speed of lithium ions in the electrode. The copper nano-points on the surface of the carbon network can promote electron conduction, and the nitrogen-doped carbon network loaded with the copper nano-points provides a stable composite layer for the nano-silicon material, which can effectively inhibit the volume expansion of the silicon negative electrode and improve the structural stability of the silicon negative electrode.

[0024] Preferably, the size of the nano-silicon is 50-100 nm.

[0025] In a second aspect, the present application provides a preparation method of a composite silicon-based negative electrode material, comprising: mixing a copper-based nitrogen heterocyclic crown ether complex and nano-silicon, and sintering under a protective atmosphere to obtain the same.

[0026] The inventors have found that the copper-based nitrogen heterocyclic crown ether complex is selected as one of the raw materials, and in the sintering process, the copper-based nitrogen heterocyclic crown ether complex is cracked into a carbon network doped with nitrogen elements, and the carbon network is uniformly loaded with nano-copper. The carbon network and the nano-silicon are combined to obtain a silicon-based negative electrode material with good electrical conductivity and structural stability, which improves the cycle performance of the battery.

[0027] Preferably, the mass ratio of the copper-based nitrogen heterocyclic crown ether complex to the nano-silicon is (0.1-0.8) : 1.

[0028] The inventors have found that, within the above preferred range, the nano-silicon and the copper-based azacrown ether complex can be uniformly mixed, and sufficient carbon network can be generated to uniformly distribute the nano-silicon and reduce the possibility of agglomeration of the nano-silicon.

[0029] Preferably, the sintering temperature is 500-700℃, and the sintering time is 5-10h.

[0030] The inventors have found that, under the above preferred sintering conditions, the organic groups in the copper-based azacrown ether complex can be completely decomposed into carbon network, the content of impurities is reduced, and each material is uniformly distributed to reduce the possibility of agglomeration.

[0031] In a specific embodiment, a method for preparing a composite silicon-based negative electrode material includes the following steps: Step 1: preparing a copper-based azacrown ether complex: mixing azacrown ether, copper salt and water, and performing coordination reaction for a certain time, then centrifuging, washing with water and drying to obtain the copper-based azacrown ether complex; Step 2: preparing a composite silicon-based negative electrode material: mixing the copper-based azacrown ether complex prepared in Step 1 and nano-silicon, and sintering under a protective atmosphere to obtain the composite silicon-based negative electrode material.

[0032] Preferably, the azacrown ether is any one or two or more of pyridine-azacrown ether, azo-18-crown ether-6, 4,13-diazo-18-crown-6-ether, and azo-15-crown ether-5.

[0033] Preferably, the copper salt is any one or two or more of copper sulfate, copper chloride and copper nitrate.

[0034] Preferably, the molar ratio of azacrown ether to copper salt is (5-10):1.

[0035] Preferably, the coordination reaction time is 10-20h.

[0036] In actual application, the coordination reaction is performed at room temperature.

[0037] Preferably, the gas for providing the protective atmosphere is any one or both of nitrogen and argon.

[0038] In a third aspect, the present application provides a battery comprising the above composite silicon-based negative electrode material.

[0039] To make the technical problems, technical solutions and technical advantages of the present application clearer, specific examples will be described in detail below, but the protection scope of the present application is not limited to the following specific examples.

[0040] Unless otherwise defined, all terms used in the disclosure, including technical and scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art. The terms used in the present disclosure are only for the purpose of describing specific embodiments and are not intended to limit the scope of the present disclosure.

[0041] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present disclosure can be purchased on the market or prepared by existing methods.

[0042] Example 1: A preparation method of a composite silicon negative electrode, comprising the following steps: Step 1, 0.2 mol of pyridine-azacrown ether is dissolved in 500 ml of deionized water, 0.03 mol of copper sulfate is added to the above aqueous solution, and after 15 h of coordination reaction, the copper-based pyridine-azacrown ether complex is obtained by centrifugation, water washing and drying.

[0043] Step 2, 3 g of the copper-based pyridine-azacrown ether complex prepared in step 1 is mixed with 10 g of nano-silicon material, and then sintered at 550°C under nitrogen atmosphere for 7 h to obtain a composite silicon-based negative electrode material.

[0044] Figure 1 The SEM image of the composite silicon negative electrode material prepared in Example 1 is shown in Figure 1. Figure 1 It can be seen that the D50 of the silicon particles is about 50-100 nm, and the silicon particles are uniformly distributed inside the carbon network.

[0045] Figure 2 The EDS image of the composite silicon negative electrode material prepared in Example 1 is shown in Figure 2. Figure 2 It can be seen that Cu, N, C and Si are uniformly distributed in the material. The distribution of Cu and N overlaps with the distribution of C, which proves that the copper-based azacrown ether complex provided by the present disclosure is cracked into a carbon network containing N elements under the calcination process, and the carbon network is loaded with Cu.

[0046] Comparative Example 1: A preparation method of a composite silicon negative electrode, comprising the following steps: Step 1, 3 g of pyridine-azacrown ether is mixed with 10 g of nano-silicon material, and then sintered at 550°C under nitrogen atmosphere for 7 h to obtain a composite silicon-based negative electrode material.

[0047] Comparative Example 2: A preparation method of a composite silicon negative electrode, comprising the following steps: Step 1, 1.2 g of nano-copper and 10 g of nano-silicon material are mixed, and then sintered at 550°C under nitrogen atmosphere for 7 h to obtain a composite silicon-based negative electrode material.

[0048] Comparative Example 3: A preparation method of a composite silicon negative electrode, comprising the following steps: Step 1, 1.2g of nano-copper, 0.2mol of pyridine-azacrown ether and 10g of nano-silicon material are mixed and sintered at 550℃ under nitrogen atmosphere for 7h to obtain a composite silicon-based negative electrode material.

[0049] Example 2: A preparation method of a composite silicon negative electrode, comprising the following steps: Step 1, 0.2mol of azacrown-18-ether-6 is dissolved in 500ml of deionized water, 0.02mol of copper chloride is added to the above aqueous solution, and after 10h of coordination reaction, the copper-based azacrown-18-ether-6 complex is obtained by centrifugation, water washing and drying.

[0050] Step 2, 1g of the copper-based azacrown-18-ether-6 complex prepared in step 1 is mixed with 10g of nano-silicon material and sintered at 500℃ under nitrogen atmosphere for 10h to obtain a composite silicon-based negative electrode material.

[0051] Example 3: A preparation method of a composite silicon negative electrode, comprising the following steps: Step 1, 0.2mol of 4,13-diazacrown-18-ether-6 is dissolved in 500ml of deionized water, 0.04mol of copper nitrate is added to the above aqueous solution, and after 15h of coordination reaction, the copper-based 4,13-diazacrown-18-ether-6 complex is obtained by centrifugation, water washing and drying.

[0052] Step 2, 4g of the copper-based 4,13-diazacrown-18-ether-6 complex prepared in step 1 is mixed with 5g of nano-silicon material and sintered at 700℃ under nitrogen atmosphere for 5h to obtain a composite silicon-based negative electrode material.

[0053] The silicon negative electrode materials prepared in Examples 1-3 and Comparative Examples 1-3, as well as nano-silicon, are used as active materials, which are mixed with conductive agent acetylene black (AB) and binder polyvinylidene fluoride (PVDF) in a mass ratio of 7:2:1, N-methyl pyrrolidone (NMP) is used as solvent, and the mixture is stirred in a small beaker at a speed of 800r / min for 2h to obtain a slurry. The slurry is coated on the current collector copper foil using an automatic coating machine, placed on a tempered glass and dried in a vacuum drying oven at 85℃ for 4h, then punched to prepare a 14mm diameter electrode piece, dried in a vacuum drying oven at 105℃ for 4h, placed in an argon gas-filled glove box with water content and oxygen content less than 0.1ppm for 4h to reduce the adsorbed water in the electrode piece during transfer, and then assembled into a CR2032 type button cell in the glove box. The battery uses a porous polyethylene membrane with a diameter of 18mm and a model of Celgard2300 as a separator, and lithium sheet as a counter electrode.

[0054] After the battery assembly is completed and aged for 12 h, then a charge-discharge test at a 2C rate is performed in a voltage range of 0.1-3.0 V.

[0055] Figure 3 The cycle performance test chart of the battery assembled by the silicon negative electrode material prepared in Example 1-3, Comparative Example 1-3 and nano silicon is shown in Figure 3 It can be known that, by comprehensively analyzing Example 1, Comparative Example 1-3, it is known that only doping the carbon material containing nitrogen elements or doping copper elements in the silicon negative electrode material can improve the cycle performance of the silicon negative electrode material, and doping the carbon material containing nitrogen elements and copper elements in the silicon negative electrode material can further improve the cycle performance of the silicon negative electrode material. The silicon negative electrode material provided in the application is not only doped with carbon material, but also loaded with copper nano points on the carbon material. The cycle performance of the silicon negative electrode material provided in the application with a special structure is more excellent, which fully proves that the modified silicon negative electrode material has more excellent electrochemical stability, and further proves the structural stability of the silicon negative electrode material. The electrochemical performance of the unmodified nano silicon material is the worst, which may be due to the volume expansion of the silicon negative electrode after electrochemical cycling, thereby directly affecting the electrochemical capacity retention rate.

[0056] Figure 4 The SEM chart of the electrode sheet prepared from the composite silicon negative electrode material prepared in Example 1 after 50 cycles is shown in Figure 4 It can be known from the chart that, after cycling, the surface of the electrode sheet is smooth and no cracks are generated, which can prove that the composite silicon negative electrode material provided in the application has good structural stability.

[0057] Figure 5 The SEM chart of the electrode sheet prepared from the composite silicon negative electrode material prepared in Comparative Example 1 after 50 cycles is shown in Figure 5 It can be known from the chart that, after cycling, the electrode sheet has obvious cracks, which indicates that the silicon negative electrode material prepared by compounding a single nitrogen-containing carbon network and silicon material is also prone to volume expansion, and its structural stability is relatively poor compared with the composite silicon negative electrode material provided in the application.

[0058] Figure 6 The SEM chart of the electrode sheet prepared from the nano silicon after 50 cycles is shown in Figure 6 It can be known from the chart that, after cycling, the electrode sheet has obvious cracks, and the crack size is large, which will greatly affect the electrochemical performance of the material. It can be obviously seen from the electrochemical performance chart in Figure 3 that the electrochemical capacity decay is fast in the later period, which indicates that the severe expansion of the silicon negative electrode causes the irreversible structure of the silicon negative electrode, and the electrochemical reversibility is adversely affected.

[0059] Figures 3-6 ​It can be proved that the copper nanodot and nitrogen-doped carbon net provided by the application have better cycle performance and structural stability.

[0060] The above-described embodiments are merely preferred specific embodiments of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can make equivalent replacements or changes to the technical solutions and concepts of the present application within the technical scope of the present application, which should be covered within the protection scope of the present application.

Claims

1. A composite silicon-based negative electrode material, characterized in that: The invention comprises nano-silicon and carbon network, wherein the nano-silicon is distributed on the carbon network and the nano-silicon and the carbon network are tightly combined; the carbon network is doped with nitrogen element, and the surface of the carbon network is loaded with nano-copper.

2. The composite silicon-based negative electrode material according to claim 1, characterized in that The size of the nano-silicon is 50-100 nm.

3. A method for preparing a composite silicon-based negative electrode material, characterized in that: The copper-based nitrogen crown ether complex and nano-silicon are mixed and sintered under a protective atmosphere to obtain the product.

4. The method for preparing a composite silicon-based negative electrode material according to claim 3, wherein: The mass ratio of the copper-based azacrown ether complex to nano-silicon is (0.1-0.8):

1.

5. The method for preparing the composite silicon-based negative electrode material according to claim 3, wherein: The sintering temperature is 500~700℃ and the sintering time is 5~10h.

6. The method for preparing the composite silicon-based negative electrode material according to claim 3, wherein: The preparation method of the copper-based azacrown ether complex comprises the following steps: mixing azacrown ether, copper salt and water, performing coordination reaction for a certain period of time, centrifuging, washing with water and drying to obtain the complex.

7. The method for preparing the composite silicon-based negative electrode material according to claim 6, wherein: The azacrown ether is any one or more of pyridine-azacrown ether, aza-18-crown-6, 4,13-diaza-18-crown-6, and aza-15-crown-5; the copper salt is any one or more of copper sulfate, copper chloride, and copper nitrate; and the molar ratio of the azacrown ether to the copper salt is (5-10):

1.

8. The method for preparing the composite silicon-based negative electrode material according to claim 6, wherein: The coordination reaction time is 10~20h.

9. A battery, characterized in that: The invention comprises the composite silicon-based negative electrode material according to any one of claims 1 to 2 or the composite silicon-based negative electrode material prepared by the preparation method according to any one of claims 3 to 8.

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