Silicon-carbon negative electrode active material and preparation method thereof, silicon-carbon negative electrode material and battery

Abstract

The present invention belongs to the field of lithium battery technology and discloses a silicon-carbon negative electrode active material, which is mainly prepared from the following components: SiO, a polymer, and a titanate; the polymer has the following structural unit: #imgabs0#, wherein R1, R2, R3, and R4 are all selected from H, an alkyl group, a halogen, or a halogenated alkyl group; the titanate has the following general structural formula: #imgabs1#, wherein X is selected from a monoalkoxy group, an oxyacetic acid chelate group, or an oxalic acid chelate group, and Y is selected from a fatty acid ester group, a phosphate group, a pyrophosphate group, or a phosphite group, and 1≤m≤4, and m+n≤6. The present invention adds titanate to SiO and a polymer, causing the three to undergo an in-situ coupling reaction. That is, the titanate acts as a bridge connecting SiO and the polymer, and is directional bonded to organic and inorganic substances through chemical bonds, thereby enhancing the binding force between SiO and carbon in the silicon-carbon negative electrode material and reducing the risk of material expansion and pulverization and silicon-carbon separation during battery cycling.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium batteries and relates to a silicon-carbon negative electrode active material and a preparation method thereof, a silicon-carbon negative electrode material and a battery. Background Art

[0002] Lithium-ion batteries are widely used in many fields due to their many advantages, such as light weight, high energy density, high power density, and long life. However, with the rapid development of portable electronic devices and electric vehicles, the demand for high-energy-density lithium-ion batteries is also increasing. Commercial lithium-ion batteries with graphite as the negative electrode are approaching their energy density limit (372mAh / g), so it is necessary to explore higher-energy-density electrode materials to replace the currently used commercial materials.

[0003] Compared to graphite anode materials, silicon-based anode materials have extremely high theoretical specific capacity (3580 mAh / g at room temperature), are abundant in resources, and are low in cost. They are considered to be a promising new generation of high-energy-density anode materials. However, during the alloying process, silicon undergoes a significant volume expansion due to the insertion of lithium ions. This excessive volume change can lead to silicon-carbon separation, electrode pulverization, and even separation from the current collector, causing rapid battery capacity degradation and reduced cycle performance.

[0004] To avoid the problem of silicon-carbon separation caused by volume expansion, researchers have developed a variety of binders. However, the addition of binders usually reduces its conductivity and easily causes uneven silicon distribution. Invention patent CN114649523A discloses a silicon-carbon negative electrode material and its preparation method. The silicon-carbon negative electrode material is composed of silicon powder and porous carbon. The silicon powder is distributed in the pores of the porous carbon. The pores can provide a buffer space for silicon expansion and improve its electrochemical stability. However, the presence of the pores will lead to poor contact between silicon and carbon, which will greatly reduce the performance of the silicon-carbon negative electrode material.

[0005] Therefore, it is necessary to study a new method for preparing highly stable silicon-carbon negative electrode materials, improve the interface between silicon and carbon materials in silicon-carbon negative electrode materials, and effectively solve the silicon-carbon separation problem caused by volume expansion. Summary of the Invention

[0006] The present invention aims to provide a silicon-carbon negative electrode active material in which titanate serves as a bridge connecting SiO and polymer, thereby enhancing the binding force between SiO and carbon in the silicon-carbon negative electrode active material and reducing the risk of material expansion and pulverization and silicon-carbon separation during battery cycling. The lithium-ion battery obtained using the material exhibits high rate performance and very stable cycle performance.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a silicon-carbon negative electrode active material, which is mainly prepared from the following components: SiO, polymer, and titanate;

[0009] The polymer has the following structural units:

[0010]

[0011] wherein R1, R2, R3 and R4 are all selected from H, alkyl, halogen or haloalkyl;

[0012] The titanate has the following general structural formula:

[0013] X m TiY n ,

[0014] Wherein, X is selected from one of monoalkoxy, oxyacetic acid chelate or oxalic acid chelate, Y is selected from one of fatty acid ester, phosphate, pyrophosphate or phosphite, and 1≤m≤4, m+n≤6.

[0015] In one technical solution, the molar ratio of the polymer to the titanate is (1-5):1. When the amount of titanate added is too low, SiO2 and the polymer cannot be effectively connected, resulting in uneven dispersion and poor conductivity of the silicon-carbon material. This can easily lead to expansion and pulverization, as well as silicon-carbon separation, during battery cycling. When the amount of titanate added is too high, on the one hand, raw materials will be wasted, and on the other hand, the excess titanate will cause self-polymerization side reactions, which will have a negative effect on the performance of the silicon-carbon material.

[0016] In one technical solution, the polymer is polyethylene glycol, polyfluoroethylene glycol or polychloroethyl glycol.

[0017] The present invention adds titanate to SiO and a polymer, causing an in-situ coupling reaction among the three. That is, the titanate acts as a bridge connecting SiO and the polymer, and is directionally combined with organic and inorganic substances through chemical bonds, so that the SiO particles are evenly dispersed, the binding force between SiO and carbon in the silicon-carbon negative electrode active material is enhanced, and the risk of material expansion and pulverization and silicon-carbon separation during battery cycling is reduced.

[0018] Taking SiO and monoalkoxy titanate (RO-Ti-(OCOR')3) as an example, R and R' represent alkyl groups, and the polymer is represented by Y. The in situ coupling reaction is as follows:

[0019] RO-Ti-(OCOR')3+Si-OH+Y→SiO-Ti-(OCOY)3.

[0020] In a second aspect, the present invention provides a method for preparing the above-mentioned silicon-carbon negative electrode active material, comprising the following steps:

[0021] 1) mixing the ball-milled SiO powder with a polymer, titanate, and deionized water, and reacting at 60-80° C. for 24-48 hours to obtain a mixed solution; the mass ratio of the ball-milled SiO powder to the polymer is (1-50):(1-50);

[0022] 2) heating the mixed solution obtained in step 1) in an open state with stirring to obtain a solid mixture;

[0023] 3) The solid mixture obtained in step 2) is transferred to a crucible, carbonized at 700-1200° C. in an argon atmosphere for 0.5-4 h, and then naturally cooled to room temperature. The obtained solid is ground and sieved to obtain a silicon-carbon negative electrode active material.

[0024] In one technical solution, the ball milling time in step 1) is 8 to 18 hours. If the ball milling time is too short, the SiO particles become larger and the volume effect cannot be effectively suppressed. If the ball milling time is too long, the SiO particles undergo plastic deformation, which reduces their electrochemical performance.

[0025] In one technical solution, the heating rate of the carbonization process in step 3) is 1 to 10°C / min.

[0026] In a third aspect, the present invention provides a silicon-carbon negative electrode material, comprising a silicon-carbon negative electrode active material prepared by the above-mentioned method for preparing the silicon-carbon negative electrode active material, conductive carbon black, and a binder.

[0027] In one technical solution, the binder is polyvinylidene fluoride.

[0028] In one technical solution, the mass ratio of the silicon-carbon negative electrode active material, the conductive carbon black and the binder is 8:1:1.

[0029] In a fourth aspect, the present invention provides a lithium-ion battery comprising: a positive electrode; a negative electrode prepared from the above-mentioned silicon-carbon negative electrode material; a separator; a current collector; and an electrolyte.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] The present invention adds titanate to SiO and a polymer, causing an in-situ coupling reaction among the three. That is, the titanate acts as a bridge connecting SiO and the polymer, and combines with organic and inorganic substances through chemical bonds, thereby enhancing the binding force between SiO and carbon in the silicon-carbon negative electrode active material and reducing the risk of material expansion and pulverization and silicon-carbon separation during battery cycling.

[0032] The interface between SiO and carbon materials in the silicon-carbon negative electrode active material of the present invention is highly fused, and the conductivity is good. When applied to lithium-ion batteries, the material exhibits high rate performance and very stable cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is an SEM image of the silicon-carbon negative electrode active material prepared in Example 1 of the present invention.

[0034] Figure 2 This is an SEM image of the silicon-carbon negative electrode active material prepared in Comparative Example 1.

[0035] Figure 3 This is an SEM image of the silicon-carbon negative electrode active material prepared in Comparative Example 2.

[0036] Figure 4 This is a lithium-ion battery cycle performance diagram of the silicon-carbon negative electrode active material provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0037] The following examples are used to illustrate the present invention but are not intended to limit the scope of protection of the present invention. Unless otherwise specified, the technical means used in the examples are conventional means well known to those skilled in the art. The test methods in the following examples are all conventional methods unless otherwise specified.

[0038] Example 1 Preparation of silicon-carbon negative electrode active material

[0039] (1) Weigh 0.5 g of SiO powder after ball milling for 12 h, dissolve it and 2 g of polyethylene glycol with a molar mass of 1000 g / mol in 9 g of deionized water, slowly add 0.1932 g of titanate TC-F (structural formula: (CH3)2CHOTi(OOCR)3, R is an alkyl group, belonging to the plant acid type monoalkoxy titanate, molar mass: 284 g / mol) solution dropwise thereto, heat to 60 °C under continuous stirring conditions and keep warm for 24 h at a stirring rate of 700 r / min and a heating rate of 10 °C / min to obtain solution A.

[0040] (2) Solution A was transferred to an open beaker, heated to 90°C with continuous stirring, and kept warm until a solid mixture B was obtained.

[0041] (3) The solid mixture B was transferred to a crucible, and the crucible was placed in a tube furnace for carbonization under argon atmosphere protection. The temperature was raised to 900°C at a heating rate of 3°C / min and kept warm for 2 hours. The obtained solid was ground and sieved to obtain a silicon-carbon negative electrode active material.

[0042] The SEM image of the silicon-carbon negative electrode active material prepared in this embodiment is as follows: Figure 1 shown.

[0043] Example 2 Preparation of silicon-carbon negative electrode active material

[0044] This embodiment is basically the same as embodiment 1, except that: in this embodiment, the titanate TC-F is replaced by an equal molar amount of the titanate TC-114 (structural formula: (CH3)2CHOTi[OOP(OH)PO(OR)2]3, R is an alkyl group, and it belongs to the phosphoric acid type monoalkoxy titanate).

[0045] Example 3 Preparation of silicon-carbon negative electrode active material

[0046] This embodiment is basically the same as embodiment 1, except that: in this embodiment, the titanate TC-F is replaced by an equal molar amount of the titanate TC-WT (structural formula: R is an alkyl group, belonging to chelate 200 type titanate).

[0047] Example 4 Preparation of silicon-carbon negative electrode active material

[0048] This embodiment is basically the same as embodiment 1, except that: in this embodiment, the titanate TC-F is replaced by an equal molar amount of titanate TC-27 (structural formula: R is an alkyl group, belonging to a composite monoalkoxy titanate

[0049] Example 5 Preparation of silicon-carbon negative electrode active material

[0050] This embodiment is substantially the same as embodiment 1, except that: in this embodiment, the titanate TC-F is replaced by an equimolar amount of titanate TC-311 (a chelated phosphate titanium coupling agent with multiple active groups).

[0051] Example 6 Preparation of Silicon-Carbon Negative Electrode Active Material

[0052] This embodiment is basically the same as embodiment 1, except that: in this embodiment, the titanate TC-F is replaced by an equal molar amount of titanate TC-70 (a composite phosphoric acid type monoalkoxy titanate containing multiple active groups).

[0053] Example 7 Preparation of Silicon-Carbon Negative Electrode Active Material

[0054] This embodiment is substantially the same as embodiment 1, except that in this embodiment, the amount of titanate TC-F added is 0.5678 g (the molar ratio of TC-F to polyethylene glycol is 1:1).

[0055] Example 8 Preparation of Silicon-Carbon Negative Electrode Active Material

[0056] This embodiment is substantially the same as embodiment 1, except that in this embodiment, the amount of titanate TC-F added is 0.1136 g (the molar ratio of TC-F to polyethylene glycol is 1:5).

[0057] Example 9 Preparation of Silicon-Carbon Negative Electrode Active Material

[0058] (1) Weigh 2 g of SiO powder after ball milling for 10 h, dissolve it and 2 g of polyfluoroethylene glycol with a molar mass of 2000 g / mol in 12 g of deionized water, slowly add 0.1436 g of titanate TC-201 solution dropwise thereto, heat to 70 °C under continuous stirring conditions and keep warm for 48 h at a stirring rate of 900 r / min and a heating rate of 10 °C / min to obtain solution A.

[0059] (2) Solution A was transferred to an open beaker, heated to 90°C with continuous stirring, and kept warm until a solid mixture B was obtained.

[0060] (3) The solid mixture B was transferred to a crucible, and the crucible was placed in a tube furnace for carbonization under argon atmosphere protection. The temperature was raised to 1000°C at a heating rate of 5°C / min and kept warm for 1 hour. The obtained solid was ground and sieved to obtain a silicon-carbon negative electrode material.

[0061] Example 10 Preparation of silicon-carbon negative electrode active material

[0062] (1) 3 g of SiO powder ball-milled for 16 h was weighed and dissolved in 14 g of deionized water with 2 g of poly(ethylene glycol) (3000 g / mol). 0.1992 g of TC-TTS titanate solution was slowly added dropwise. The mixture was heated to 80 °C and kept warm for 24 h under continuous stirring at a stirring rate of 500 r / min and a heating rate of 5 °C / min to obtain solution A.

[0063] (2) Solution A was transferred to an open beaker, heated to 90°C with continuous stirring, and kept warm until a solid mixture B was obtained.

[0064] (3) The solid mixture B was transferred to a crucible, and the crucible was placed in a tube furnace for carbonization under argon atmosphere at a heating rate of 7°C / min to 1100°C, and kept warm for 1.5 hours. The obtained solid was ground and sieved to obtain a silicon-carbon negative electrode material.

[0065] Comparative Example 1

[0066] This example is basically the same as Example 1, except that the titanate TC-F solution is not included in this comparative example. The SEM image of the silicon-carbon negative electrode active material prepared in this comparative example is shown in FIG. Figure 2 shown.

[0067] contrast Figure 1 and Figure 2It can be seen that when titanate is added to the silicon-carbon negative electrode active material, the SiO particles are evenly dispersed after carbonization and are highly fused with the carbon material interface. However, when no titanate is added, the SiO particles agglomerate after carbonization and cannot form an effective bond with the carbon material, increasing the risk of material expansion and pulverization and silicon-carbon separation during battery cycling.

[0068] Comparative Example 2

[0069] This example is basically the same as Example 1, except that: in this comparative example, the SiO used was not ball-milled. The SEM image of the silicon-carbon negative electrode active material prepared in this comparative example is shown in FIG. Figure 3 shown.

[0070] contrast Figure 1 and Figure 3 It can be seen that the SiO particles before ball milling are severely aggregated and cannot fuse with the interface of carbon materials, while the interface of SiO and carbon materials after ball milling is highly fused, indicating that the SiO particles after ball milling are smaller in size and easier to combine with carbon materials.

[0071] Comparative Example 3

[0072] (1) 1 g of SiO powder ball-milled for 12 h was weighed and dissolved in 9 g of deionized water with 2 g of polyethylene glycol (1000 g / mol). 0.1932 g of the titanate TC-F solution was slowly added dropwise. The mixture was heated to 60 °C and kept warm for 24 h under continuous stirring at a stirring rate of 700 r / min and a heating rate of 10 °C / min to obtain solution A.

[0073] (2) Solution A was transferred to an open beaker, heated to 90°C with continuous stirring, and kept warm until a solid mixture was obtained, namely the silicon / polymer composite material.

[0074] Performance Testing

[0075] 1. Preparation of silicon-carbon negative electrode sheet:

[0076] Weigh a certain amount of silicon-carbon anode material, conductive carbon black, and polyvinylidene fluoride and place them in a ball mill. The mass ratio of silicon-carbon anode material, conductive carbon black, and polyvinylidene fluoride is 8:1:1. Add a certain amount of N-methylpyrrolidone and ball milling beads (the ratio of large ball milling beads, medium ball milling beads, and small ball milling beads is 1:4:8) to the ball mill. After ball milling, use a scraper to evenly coat the slurry on a metal copper foil. Dry it at 80°C for 8 hours, then cut it into discs with a diameter of 14mm. Then dry it in a vacuum oven at 80°C for 10 hours. The prepared silicon-carbon anode sheet needs to be stored in an argon-protected glove box with a water and oxygen content of less than 0.1ppm until ready for use.

[0077] 2. Preparation of electrolyte:

[0078] All operations were performed in a glove box with water and oxygen concentrations below 0.1 ppm. Solvent A was prepared by mixing ethylene carbonate, fluoroethylene carbonate, and diethyl carbonate in a mass ratio of 3:1:6. 1.2 mol / L of lithium salt LiPF6 was then dissolved in solvent A. Finally, 1 wt% of lithium difluorooxalatoborate was added and mixed thoroughly.

[0079] 3. Lithium-ion battery testing:

[0080] Assembly: All operations are carried out in a glove box with a water and oxygen content of less than 0.1ppm. First, 5μL of electrolyte is dripped into the center of the positive electrode shell to fix the electrode. The prepared electrode with a diameter of 14mm is placed in the middle of the positive electrode shell. Then, 35μL of electrolyte is dripped on the electrode to wet the electrode. Then, a Celgard 2325 (PP / PE / PP three-layer) separator with a diameter of 16mm is placed in the center of the positive electrode shell on the electrode. 40μL of electrolyte is dripped again to wet the separator. Then, a 15.8×5.8mm metal lithium sheet is placed on top of the separator in the center of the positive electrode shell. Then, a nickel foam with a diameter of 14mm is placed on top of the metal lithium sheet. Finally, the battery negative electrode shell is buckled on the positive electrode shell, placed in a mold, and pressed and sealed. The lithium-ion battery is completed.

[0081] Test: The prepared lithium-ion battery was set aside for 24 hours, and then the charge and discharge test was carried out on the Xinwei software tester using the discharge-first-charge program. It went through a formation stage before cycling (three weeks at 0.1C), and was left to stand for 1 minute between the completion of discharge and the start of the next charge. The charge and discharge voltage was 0.01~2V.

[0082] The cycle performance of the lithium-ion battery assembled with the silicon-carbon negative electrode active material prepared in Example 1 at room temperature and 5C rate is shown in the figure below: Figure 4 As shown. Figure 4 It can be seen that the silicon-carbon negative electrode prepared by the silicon-carbon negative electrode active material provided by the present invention can be stably cycled for more than 500 cycles, and the capacity retention rate exceeds 63%.

[0083] The performance test results of the assembled lithium-ion batteries of Examples 1 to 10 and Comparative Examples 1 to 3 are shown in Table 1.

[0084] Table 1 Performance test results of the assembled lithium ion batteries of Examples 1 to 10 and Comparative Examples 1 to 3

[0085]

[0086] As can be seen from Table 1, after titanate is omitted from the silicon-carbon negative electrode active material in Comparative Example 1, the cycle performance of the lithium battery is greatly reduced, while different types or amounts of titanate are added in Examples 1 to 10, and the cycle performance of the lithium battery is quite stable. It can be seen that titanate acts as a bridge connecting SiO and polymer, which enhances the binding force between SiO and carbon in the silicon-carbon negative electrode active material, and helps to improve the cycle performance of the lithium battery; SiO in Comparative Example 2 is not pretreated by ball milling, and SiO in Examples 1 to 10 are all pretreated by ball milling. Although the first discharge capacity of the lithium battery prepared by Comparative Document 2 is not much different from that of Examples 1 to 10, the cycle performance of the lithium battery is greatly reduced. It can be seen that the use of ball-milled SiO reduces the particle size of SiO, which also helps to enhance the binding force between SiO and carbon in the silicon-carbon negative electrode material, thereby improving the cycle performance of the lithium battery; the lithium battery of the uncarbonized polymer in Comparative Example 3 has no cycle performance, which indicates that the failure to carbonize the polymer will increase electrode side reactions, hinder ion transfer, and seriously affect battery performance.

[0087] The embodiments described above are only preferred embodiments of the present invention and are only used to explain the present invention, not to limit the scope of implementation of the present invention. For those skilled in the art, it is of course possible to easily make other implementation methods by replacing or changing the technical content disclosed in this specification. Therefore, all changes and improvements made on the principles of the present invention should be included in the scope of the patent application of the present invention.

Claims

1. A silicon-carbon negative electrode active material, characterized in that: It is mainly prepared from the following components: SiO, polymer, titanate; The polymer has the following structural units: ， wherein R1, R2, R3 and R4 are all selected from H, alkyl, halogen or haloalkyl; The titanate has the following general structural formula: ， wherein X is selected from a monoalkoxy group, an oxyacetic acid chelate group, or an oxalic acid chelate group, and Y is selected from a fatty acid ester group, a phosphate group, a pyrophosphate group, or a phosphite group, and 1≤m≤4, and m+n≤6; The preparation method of the silicon-carbon negative electrode active material comprises the following steps: 1) Mixing the ball-milled SiO powder with a polymer, titanate, and deionized water, and reacting at 60-80°C for 24-48 hours to obtain a mixed solution; the mass ratio of the ball-milled SiO powder to the polymer is (1-50):(1-50); 2) heating the mixed solution obtained in step 1) in an open state with stirring to obtain a solid mixture; 3) The solid mixture obtained in step 2) is transferred to a crucible and carbonized in an argon atmosphere at 700-1200° C. for 0.5-4 h, and then naturally cooled to room temperature. The obtained solid is ground and sieved to obtain a silicon-carbon negative electrode active material.

2. The silicon-carbon negative electrode active material according to claim 1, characterized in that The molar ratio of the polymer to the titanate is (1-5):

1.

3. The silicon-carbon negative electrode active material according to claim 1, characterized in that The polymer is polyethylene glycol, polyfluoroethylene glycol or polychloroethyl glycol.

4. The silicon-carbon negative electrode active material according to claim 1, characterized in that The ball milling time in step 1) is 8 to 18 hours.

5. The silicon-carbon negative electrode active material according to claim 1, characterized in that The heating rate of the carbonization process in step 3) is 1-10°C / min.

6. A silicon-carbon negative electrode material, characterized in that: The invention comprises the silicon-carbon negative electrode active material according to any one of claims 1 to 5, conductive carbon black and a binder.

7. The silicon-carbon negative electrode material according to claim 6, characterized in that The binder is polyvinylidene fluoride.

8. The silicon-carbon negative electrode material according to claim 6, characterized in that The mass ratio of the silicon-carbon negative electrode active material, the conductive carbon black and the binder is 8:1:

1.

9. A lithium-ion battery, characterized in that: include: positive electrode; A negative electrode prepared from the silicon-carbon negative electrode material according to any one of claims 6 to 8; diaphragm; current collector; as well as electrolyte.

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