Silicon-carbon negative electrode material with in-situ grown onion carbon layer structure and preparation method thereof
By growing an onion-like carbon layer structure in situ in silicon-based anode materials, the structural damage caused by volume effects in silicon-based anode materials in lithium-ion batteries is solved, thereby improving the cycle stability and first-cycle efficiency of the materials.
Patent Information
- Application Number
- CN202110818760.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2021-07-20
- Publication Date
- 2026-01-09
- Estimated Expiration
- 2041-07-20
AI Technical Summary
Silicon-based anode materials suffer structural damage and reduced cycle life in lithium-ion batteries due to volume effects. Existing modification methods are costly and difficult to apply on a large scale.
The silicon-carbon anode material adopts an in-situ grown onion carbon layer structure. The core is a composite sphere of silicon-based material and low-carbon carbon source, and the outer shell is an onion carbon layer. The pores left after the low-carbon carbon source is carbonized provide a buffer space, and the onion carbon layer supports the structure and reduces the formation of SEI film.
This improved the stability of the anode material during cycling, reduced the formation of the SEI film, and enhanced the structural stability and cycling performance.
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Figure CN115642231B_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of materials, in particular to a silicon-carbon negative electrode material with in-situ grown onion carbon layer structure and a preparation method thereof. BACKGROUND
[0002] Silicon or silicon monoxide as a lithium ion battery negative electrode material has extremely high theoretical reversible capacity, among which, silicon material is as high as 4200 mAh / g. However, the silicon-based negative electrode material has a huge volume effect in the process of deintercalating lithium, which destroys the negative electrode particle structure in the charging and discharging process, causes the negative electrode to be pulverized and invalid, and leads to the decrease of battery cycle performance.
[0003] At present, the modification of silicon-based materials is continuously carried out. The document (H. Li, X. J. Huang, L. Q. Chen, Z. G. Wu, Y Liang, Electr Chem. and Solid-State Lett., 2, 547-549 (1999)) records that Li et al. prepared a negative electrode material by using nano-silicon particles, which can reduce the volume effect, improve the cycle performance of the silicon-based negative electrode material, and maintain a high reversible capacity (1700 mAh / g). However, this method has high cost, and nano-silicon particles are not easy to prepare, so the industry is still exploring other improvement methods. SUMMARY
[0004] The present application provides a silicon-carbon negative electrode material with in-situ grown onion carbon layer structure and a preparation method thereof. The pores left after the carbonization of the low-residual carbon source in the core of the present application can provide a buffer space for the expansion of the silicon-based material. The complete onion carbon layer structure of the shell plays a supporting role, and can prevent the contact between the electrolyte and the silicon particles to form a large amount of solid electrolyte interface (SEI) film, and has a small specific surface area and surface impurities, further reducing the formation of SEI film, and greatly improving the stability of the negative electrode material in the cycle process.
[0005] In a first aspect, the present application provides a silicon-carbon negative electrode material with in-situ grown onion carbon layer structure, which comprises a core and a shell.
[0006] The core is a composite sphere of silicon-based material and carbon material, and the particle size of the composite sphere is in the range of 1 μm to 50 μm; wherein the raw material of the carbon material is a low-residual carbon source, and the core has pores formed after the carbonization of the low-residual carbon source;
[0007] The shell is an in-situ grown onion carbon layer structure, and the thickness of the onion carbon layer is 1 nm to 1000 nm.
[0008] The particle size of the silicon-carbon negative electrode material is in the range of 1 μm to 100 μm.
[0009] Preferably, the silicon-based material comprises one or more of silicon, silicon monoxide, modified silicon monoxide or amorphous silicon alloy;
[0010] The low-residual carbon carbon source has a residual carbon rate of ≤20% at 900℃.
[0011] Further preferably, the low-residual carbon carbon source specifically comprises one or more of glucose, sucrose, polyvinylpyrrolidone or sodium carboxymethyl cellulose.
[0012] In a second aspect, the present application provides a preparation method of the silicon-carbon negative electrode material with in-situ grown onion carbon layer structure as described in the first aspect, and the preparation method comprises:
[0013] After the silicon-based material and the low-residual carbon carbon source are mixed at a mass ratio of 1:0.1 to 1:10, a solvent is added, stirring is performed until the low-residual carbon carbon source is dissolved, ultrasonic treatment is then performed, and spray granulation is then performed to obtain spray particles with an average particle size of 1nm to 30μm;
[0014] The compound containing boron and / or calcium elements is mixed with the high-residual carbon polymer to perform ball milling to obtain ball-milled particles with an average particle size of 1nm to 500nm;
[0015] After the spray particles and the ball-milled particles are uniformly mixed at a mass ratio of 1:1 to 20:1, the temperature is raised to 700℃ to 1200℃ at a rate of 1℃ / min to 10℃ / min under a protective atmosphere, and after being kept at the temperature for 1 hour to 15 hours, the product is dispersed and sieved to obtain composite material particles with an average particle size of 1μm to 100μm;
[0016] The composite material particles are added to distilled water for stirring, and then filtered and dried to obtain the core-shell structure silicon-carbon composite negative electrode material with in-situ grown onion carbon layer structure.
[0017] Preferably, the mass ratio of the solid to the solvent after the silicon-based material and the low-residual carbon carbon source are added to the solvent is 1:100 to 1:100.
[0018] Preferably, the silicon-based material comprises one or more of silicon, silicon monoxide, modified silicon monoxide or amorphous silicon alloy;
[0019] The low-residual carbon carbon source has a residual carbon rate of ≤20% at 900℃, and specifically comprises one or more of glucose, sucrose, polyvinylpyrrolidone or sodium carboxymethyl cellulose.
[0020] The high-residual carbon polymer comprises one or more of pitch, phenolic resin or epoxy resin;
[0021] The compound containing boron and / or calcium elements includes one or more of boron oxide, calcium oxide, and calcium hydroxide.
[0022] Preferably, the spray granulation is specifically spray granulation by using a spray dryer.
[0023] Preferably, the stirring time is 1-20 hours, and the rotating speed is 500-2000 r / min.
[0024] In a third aspect, the present application provides a negative electrode including the silicon-carbon negative electrode material with the in-situ grown onion carbon layer structure as described in the first aspect.
[0025] In a fourth aspect, the present application provides a lithium battery including the negative electrode as described in the third aspect.
[0026] The silicon-carbon negative electrode material with the in-situ grown onion carbon layer structure provided by the present application has a silicon-based material and carbon material composite sphere as the core, the pores left after carbonization of the low-residual-carbon carbon source in the core can provide a buffer space for the expansion of the silicon-based material; the complete onion carbon layer formed shell outside plays a supporting role, and can prevent the electrolyte from contacting the silicon-carbon particles in the core to form a large number of SEI films, at the same time, the onion carbon layer has a small specific surface area and less surface impurities, which further reduces the formation of surface SEI films, greatly improves the stability of the silicon-based negative electrode material in the cycle process. The composite negative electrode material provided by the present application can be used in liquid, semi-solid, quasi-solid, and full-solid electrolyte lithium ion batteries. BRIEF DESCRIPTION OF DRAWINGS
[0027] The technical solutions of the embodiments of the present application will be further described in detail below with reference to the drawings and examples.
[0028] Figure 1 The structure schematic diagram of the silicon-carbon negative electrode material with the in-situ grown onion carbon layer structure of the embodiments of the present application;
[0029] Figure 2 The flow chart of the preparation method of the silicon-carbon negative electrode material with the in-situ grown onion carbon layer structure of the embodiments of the present application;
[0030] Figure 3 The transmission electron microscope (TEM) diagram of the silicon-carbon negative electrode material with the onion carbon layer structure provided by the embodiment 1 of the present application;
[0031] Figure 4 The capacity cycle retention diagram of the embodiment 1, the embodiment 2, and the comparative example 1 of the present application. DETAILED DESCRIPTION
[0032] The application will be further described below with reference to the accompanying drawings and specific examples, but it should be understood that these examples are only used for more detailed description and should not be understood as limiting the application in any form, i.e. not intended to limit the protection scope of the application.
[0033] The silicon-carbon negative electrode material with in-situ grown onion carbon layer structure of the application has a structure as shown in the figure, wherein the inner core is a composite sphere of silicon-based material and carbon material, the particle size of the composite sphere ranges from 1 μm to 50 μm; the shell is an in-situ grown onion carbon layer structure, the thickness of the onion carbon layer ranges from 1 nm to 1000 nm; the particle size of the silicon-carbon negative electrode material ranges from 1 μm to 100 μm. Figure 1
[0034] In the composite sphere of the inner core, the silicon-based material includes one or more of silicon, silicon monoxide, modified silicon monoxide or amorphous silicon alloy; the raw material of the carbon material is a low-residue carbon source, and the residue carbon rate of the low-residue carbon source is ≤20% at 900°C. The low-residue carbon source specifically includes one or more of glucose, sucrose, polyvinylpyrrolidone or sodium carboxymethyl cellulose.
[0035] The inner core has pores formed after carbonization of the low-residue carbon source.
[0036] The above material can be prepared by the following method, and the main steps are as shown in the figure, which include: Figure 2
[0037] In step 110, the silicon-based material and the low-residue carbon source are mixed in a mass ratio of 1:0.1 to 1:10, a solvent is added, stirring is performed until the low-residue carbon source is dissolved, ultrasonic treatment is then performed, and spray granulation is then performed to obtain spray particles with an average particle size of 1 nm to 30 μm.
[0038] In the step, the mass ratio of the solid to the solvent after the silicon-based material and the low-residue carbon source are added to the solvent is 1:100 to 1:1000.
[0039] The silicon-based material includes one or more of silicon, silicon monoxide, modified silicon monoxide or amorphous silicon alloy.
[0040] The residue carbon rate of the low-residue carbon source is ≤20% at 900°C, and the low-residue carbon source specifically includes one or more of glucose, sucrose, polyvinylpyrrolidone or sodium carboxymethyl cellulose.
[0041] The spray granulation is specifically spray granulation performed by using a spray dryer, and the outlet temperature of the spray dryer is 130°C to 200°C, and the pressure is 3 MPa to 4 MPa.
[0042] In step 120, a compound containing boron and / or calcium elements is mixed with a high-residue polymer to perform ball milling to obtain ball-milled particles with an average particle size of 1 nm to 500 nm.
[0043] The high-residue polymer includes one or more of pitch, phenolic resin or epoxy resin; and the compound containing boron and / or calcium elements includes one or more of boron oxide, calcium oxide, calcium hydroxide, etc.
[0044] The rotation speed of the ball mill is 1000 r / min to 3000 r / min, and the grinding time is 2 hours to 24 hours.
[0045] In step 130, the spray particles and the ball mill particles are mixed uniformly at a mass ratio of 1:1 to 20:1, and then heated to 700 DEG C to 1200 DEG C at a rate of 1 DEG C / min to 10 DEG C / min under a protective atmosphere, and after holding for 1 hour to 15 hours, the product is dispersed and sieved to obtain composite particles with an average particle size of 1 μm to 100 μm.
[0046] The protective atmosphere includes a nitrogen atmosphere, an argon atmosphere or other inert atmosphere.
[0047] In step 140, the composite particles are added to distilled water for stirring, and then filtered and dried to obtain a core-shell structure silicon-carbon composite negative electrode material with an in-situ grown onion carbon layer structure.
[0048] The stirring time is 1 hour to 20 hours, and the rotation speed is 500 r / min to 2000 r / min.
[0049] In the preparation method of the silicon-carbon negative electrode material, in order to ensure the grain size of the silicon particles, a compound of boron and calcium is used as a medium for forming an onion carbon layer, and water washing is used instead of high-temperature removal of impurities. In the preparation process of the material, the pores left after carbonization of the low-residue carbon source can provide a buffer space for the expansion of the silicon-based material, the complete onion carbon layer forms a shell to provide support, and prevents the electrolyte from contacting the silicon particles to form a large amount of SEI film. The onion carbon layer has a small specific surface area and surface impurities, further reducing the formation of SEI film, and greatly improving the stability of the negative electrode material in the cycle process.
[0050] In order to better understand the technical solutions provided by the present application, the following describes the specific process of preparing a silicon-carbon negative electrode material by using the method provided by the above embodiments of the present application, and the characteristics of the lithium ion battery.
[0051] Example 1
[0052] The present embodiment provides a silicon-carbon negative electrode material with an in-situ grown onion carbon layer structure, and the preparation method is as follows:
[0053] Take 100g of silicon particles with D50 = 2.3 μm, mix with glucose in a mass ratio of 1:5, add distilled water in a solid to solvent mass ratio of 1:300, stir until the glucose is completely dissolved, ultrasonic treatment for 5 minutes, spray granulation with a spray dryer, outlet temperature 150℃, pressure 3MPa, to obtain D50 = 4.5 μm spray particles;
[0054] Take 100g of boron oxide and 100g of pitch, mix and ball mill for 6 hours at 1000r / min, to obtain D50 = 200nm ball milled particles;
[0055] Heat the spray particles and ball milled particles to 1200℃ at 1℃ / min under a nitrogen atmosphere, hold for 2 hours, break up the resulting product and sieve to obtain D50 = 12.8 μm composite material particles;
[0056] Add the composite material particles to distilled water and stir for 20 hours at 500r / min, then filter and dry to obtain core-shell structure silicon-carbon composite negative electrode material particles with in-situ grown onion carbon layer structure.
[0057] Figure 3 TEM image of the silicon-carbon negative electrode material with onion carbon layer structure provided for Example 1 of the present application.
[0058] For better comparison, we prepared a comparative sample according to the following method.
[0059] Comparative Example 1
[0060] Take 100g of silicon particles with D50 = 2.3 μm, mix with glucose in a mass ratio of 1:5, add distilled water in a solid to solvent mass ratio of 1:300, stir until the glucose is completely dissolved, ultrasonic treatment for 5 minutes, spray granulation with a spray dryer, outlet temperature 150℃, pressure 3MPa, to obtain D50 = 4.5 μm spray particles;
[0061] Heat the spray particles to 1200℃ at 1℃ / min under a nitrogen atmosphere, hold for 2 hours, break up the resulting product and sieve to obtain D50 = 12.8 μm negative electrode material particles.
[0062] Example 2
[0063] This example provides a silicon-carbon negative electrode material with in-situ grown onion carbon layer structure, prepared according to the following method:
[0064] Take 100g of silicon particles with D50 = 1.3pm, mix with polyvinylpyrrolidone at a mass ratio of 1:10, add distilled water at a solid to solvent mass ratio of 1:200, stir until the polyvinylpyrrolidone is completely dissolved, ultrasonic treatment for 5 minutes, spray granulation with a spray dryer, outlet temperature 200℃, pressure 3MPa, to obtain D50 = 3.2pm spray particles;
[0065] Take 100g of boron oxide and 100g of asphalt, mix and ball mill for 24 hours at a speed of 1000r / min, to obtain D50 = 80nm ball milled particles;
[0066] Heat the spray particles and ball milled particles to 1100℃ at a rate of 10℃ / min under a nitrogen atmosphere, and hold for 1 hour, then crush and sieve the resulting product to obtain D50 = 10.6pm composite particles;
[0067] Add the composite particles to distilled water and stir for 1 hour at a speed of 2000r / min, then filter and dry to obtain core-shell structure silicon-carbon composite negative electrode material particles with in-situ grown onion carbon layer structure.
[0068] Example 3
[0069] This example provides a silicon-carbon negative electrode material with in-situ grown onion carbon layer structure, and the preparation method is as follows:
[0070] Take 100g of silicon oxide particles with D50 = 3.3pm, mix with glucose at a mass ratio of 1:0.1, add distilled water at a solid to solvent mass ratio of 1:300, stir until the glucose is completely dissolved, ultrasonic treatment for 5 minutes, spray granulation with a spray dryer, outlet temperature 150℃, pressure 3MPa, to obtain D50 = 5.5pm spray particles;
[0071] Take 100g of calcium oxide and 100g of phenolic resin, mix and ball mill for 2 hours at a speed of 2000r / min, to obtain D50 = 500nm ball milled particles;
[0072] Heat the spray particles and ball milled particles to 700℃ at a rate of 1℃ / min under a nitrogen atmosphere, and hold for 15 hours, then crush and sieve the resulting product to obtain D50 = 8.9pm composite particles;
[0073] Add the composite particles to distilled water and stir for 5 hours at a speed of 500r / min, then filter and dry to obtain core-shell structure silicon-carbon composite negative electrode material particles with in-situ grown onion carbon layer structure.
[0074] Example 4
[0075] The embodiment provides a silicon-carbon negative electrode material with an in-situ grown onion carbon layer structure, and a preparation method is as follows:
[0076] 100g of silicon particles with D50=3.5um are weighed, mixed with glucose at a mass ratio of 1:2, distilled water is added at a solid-solvent mass ratio of 1:300, stirring is performed until the glucose is completely dissolved, ultrasonic treatment is performed for 5 minutes, spray granulation is performed by using a spray dryer, the outlet temperature is 130 DEG C, the pressure is 4MPa, and D50=6.3um spray particles are obtained;
[0077] 100g of boron oxide is weighed, mixed with 100g of phenolic resin, and then ball milled for 24 hours at a rotating speed of 2000r / min, D50=20nm ball milled particles are obtained;
[0078] The spray particles and the ball milled particles are heated to 1200 DEG C at a rate of 1 DEG C / min under a nitrogen atmosphere, and then kept for 2 hours, the obtained product is broken and sieved, and D50=12.8um composite material particles are obtained;
[0079] The composite material particles are added into distilled water and stirred for 20 hours at a rotating speed of 500r / min, and then filtered and dried, so as to obtain core-shell structure silicon-carbon composite negative electrode material particles with an in-situ grown onion carbon layer structure.
[0080] Embodiment 5
[0081] The embodiment provides a silicon-carbon negative electrode material with an in-situ grown onion carbon layer structure, and a preparation method is as follows:
[0082] 100g of silicon oxide particles with D50=4.3um are weighed, mixed with polyvinylpyrrolidone at a mass ratio of 1:5, distilled water is added at a solid-solvent mass ratio of 1:300, stirring is performed until the polyvinylpyrrolidone is completely dissolved, ultrasonic treatment is performed for 5 minutes, spray granulation is performed by using a spray dryer, the outlet temperature is 150 DEG C, the pressure is 3MPa, and D50=25.6um spray particles are obtained;
[0083] 100g of calcium hydroxide is weighed, mixed with 100g of pitch, and then ball milled for 6 hours at a rotating speed of 1000r / min, D50=150nm ball milled particles are obtained;
[0084] The spray particles and the ball milled particles are heated to 800 DEG C at a rate of 1 DEG C / min under a nitrogen atmosphere, and then kept for 15 hours, the obtained product is broken and sieved, and D50=15.8um composite material particles are obtained;
[0085] The composite material particles are added into distilled water and stirred for 20 hours at a rotating speed of 500r / min, and then filtered and dried, so as to obtain core-shell structure silicon-carbon composite negative electrode material particles with an in-situ grown onion carbon layer structure.
[0086] Example 6
[0087] The present example provides a silicon-carbon negative electrode material with an in-situ grown onion carbon layer structure, and the preparation method is as follows:
[0088] Take 100g of modified silicon monoxide particles with D50=3.5pm, mix with glucose at a mass ratio of 1:10, add distilled water at a solid to solvent mass ratio of 1:300, stir until the glucose is completely dissolved, ultrasonic treatment for 5 minutes, spray granulation with a spray dryer, outlet temperature 150°C, pressure 3MPa, to obtain D50=4.5pm spray particles;
[0089] Take 100g of calcium oxide and 100g of epoxy resin, mix and ball mill for 5 hours at a speed of 1000r / min, to obtain D50=300nm ball milled particles;
[0090] Heat the spray particles and ball milled particles to 1200°C at a rate of 1°C / min under a nitrogen atmosphere, and keep the temperature for 2 hours, then crush and sieve the obtained product to obtain D50=25.6pm composite material particles;
[0091] Add the composite material particles to distilled water and stir for 20 hours at a speed of 500r / min, then filter and dry to obtain core-shell structure silicon-carbon composite negative electrode material particles with an in-situ grown onion carbon layer structure.
[0092] Example 7
[0093] The present example provides a silicon-carbon negative electrode material with an in-situ grown onion carbon layer structure, and the preparation method is as follows:
[0094] Take 100g of amorphous silicon alloy particles with D50=1.3pm, mix with glucose at a mass ratio of 1:5, add distilled water at a solid to solvent mass ratio of 1:300, stir until the glucose is completely dissolved, ultrasonic treatment for 5 minutes, spray granulation with a spray dryer, outlet temperature 200°C, pressure 4MPa, to obtain D50=3.2pm spray particles;
[0095] Take 100g of boron oxide and 100g of pitch, mix and ball mill for 16 hours at a speed of 2000r / min, to obtain D50=50nm ball milled particles;
[0096] Heat the spray particles and ball milled particles to 1000°C at a rate of 1°C / min under a nitrogen atmosphere, and keep the temperature for 2 hours, then crush and sieve the obtained product to obtain D50=4.8pm composite material particles;
[0097] The composite material particles are added into distilled water and stirred for 20 hours at a speed of 500 r / min, and then filtered and dried to obtain the core-shell structure silicon-carbon composite negative electrode material particles with the in-situ grown onion carbon layer structure.
[0098] Example 8
[0099] The example provides a silicon-carbon negative electrode material with an in-situ grown onion carbon layer structure, and the preparation method is as follows:
[0100] 100 g of silicon particles with D50 = 3.3 μm are weighed, mixed with glucose at a mass ratio of 1:5, distilled water is added at a solid to solvent mass ratio of 1:300, stirred until the glucose is completely dissolved, ultrasonic treated for 5 minutes, and spray granulation is performed by using a spray dryer, the outlet temperature is 150°C, the pressure is 3 MPa, and D50 = 6.5 μm spray particles are obtained;
[0101] 100 g of boron oxide and 100 g of phenolic resin are mixed and ball milled for 6 hours at a speed of 1000 r / min to obtain D50 = 100 nm ball milled particles;
[0102] The spray particles and the ball milled particles are heated to 1200°C at a rate of 1°C / min under a nitrogen atmosphere, and then kept for 6 hours, the obtained product is broken and sieved to obtain D50 = 44.3 μm composite material particles;
[0103] The composite material particles are added into distilled water and stirred for 20 hours at a speed of 500 r / min, and then filtered and dried to obtain the core-shell structure silicon-carbon composite negative electrode material particles with the in-situ grown onion carbon layer structure.
[0104] Example 9
[0105] The example provides a silicon-carbon negative electrode material with an in-situ grown onion carbon layer structure, and the preparation method is as follows:
[0106] 100 g of silicon particles with D50 = 3.3 μm are weighed, mixed with glucose at a mass ratio of 1:5, distilled water is added at a solid to solvent mass ratio of 1:300, stirred until the glucose is completely dissolved, ultrasonic treated for 5 minutes, and spray granulation is performed by using a spray dryer, the outlet temperature is 150°C, the pressure is 3 MPa, and D50 = 6.5 μm spray particles are obtained;
[0107] 100 g of boron oxide and 100 g of phenolic resin are mixed and ball milled for 6 hours at a speed of 1000 r / min to obtain D50 = 100 nm ball milled particles;
[0108] The spray particles and the ball-milled particles are heated to 1200°C at a rate of 10°C / min under a nitrogen atmosphere, and then held for 2 hours. The resulting product is broken up and sieved to obtain D50 = 18.9 μm composite particles.
[0109] The composite particles are added to distilled water and stirred at a speed of 500 r / min for 20 hours, and then filtered and dried to obtain core-shell structure silicon-carbon composite negative electrode material particles with in-situ grown onion carbon layer structure.
[0110] Example 10
[0111] The present example provides a silicon-carbon negative electrode material with in-situ grown onion carbon layer structure, and the preparation method is as follows:
[0112] 100 g of silicon particles with D50 = 1.3 μm are mixed with glucose at a mass ratio of 1:10, and then distilled water is added at a solid-to-solvent mass ratio of 1:300. The mixture is stirred until the glucose is completely dissolved, and then ultrasonic treatment is performed for 5 minutes. Spray granulation is performed using a spray dryer, with an outlet temperature of 150°C and a pressure of 3 MPa, to obtain D50 = 6.5 μm spray particles.
[0113] 100 g of calcium oxide and 100 g of phenolic resin are mixed and ball-milled at a speed of 1000 r / min for 20 hours to obtain D50 = 40 nm ball-milled particles.
[0114] The spray particles and the ball-milled particles are heated to 1200°C at a rate of 10°C / min under a nitrogen atmosphere, and then held for 2 hours. The resulting product is broken up and sieved to obtain D50 = 18.9 μm composite particles.
[0115] The composite particles are added to distilled water and stirred at a speed of 500 r / min for 20 hours, and then filtered and dried to obtain core-shell structure silicon-carbon composite negative electrode material particles with in-situ grown onion carbon layer structure.
[0116] The materials prepared in the examples and comparative examples, and commercially available graphite A are mixed in a proportion to obtain a lithium ion battery negative electrode material with a specific capacity of 350 mAh / g. Carbon black, carboxymethyl cellulose sodium, and butadiene-styrene rubber are uniformly mixed in a polyvinylidene fluoride (PVDF) solvent at mass ratios of 2%, 2%, and 3%, respectively, to form a battery slurry. The slurry is coated on a copper foil, dried, and then cut into a circular sheet with a diameter of 14 mm. The lithium sheet is assembled into a coin cell battery in a glove box after vacuum drying at 100°C for 12 hours. The structure and electrochemical performance of the battery are evaluated by testing, and the results are recorded in Table 1.
[0117]
[0118]
[0119] Table 1
[0120] It can be seen from the comparison of the results of the comparative example and the examples that the core-shell structure of the in-situ grown onion carbon layer on the silicon-carbon negative electrode material ensures the stability of the structure, further reduces the irreversible capacity, and achieves the purpose of improving the first cycle efficiency and cycle stability.
[0121] Figure 3 The TEM image of the silicon-carbon negative electrode shows that the amorphous structure of the outermost layer of the silicon-carbon negative electrode is converted into an onion carbon layer structure, thereby reducing the formation of the SEI film and the adsorption of impurities on the surface, reducing the irreversible capacity, and improving the first cycle efficiency.
[0122] The lithium ion batteries prepared by using the negative electrode materials of Example 1, Example 2 and Comparative Example 1 as the negative electrode were compared in terms of cycle performance. The test was carried out at 25℃ in the range of 1.5-4.2V, and the capacity retention rate after 500 cycles was as shown in Table 1. Figure 4 It can be seen that the cycle capacity retention rates of the silicon-carbon negative electrode materials of Example 1 and Example 2 after 200 cycles can still reach more than 90% and 80%, respectively, which is much better than that of Comparative Example 1.
[0123] The above-described specific embodiments further illustrate the purposes, technical solutions and beneficial effects of the present application. It should be understood that the above-described embodiments are merely specific embodiments of the present application and are not intended to limit the protection scope of the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.
Claims
1. A method for preparing a silicon-carbon anode material with an in-situ grown onion-like carbon layer structure, characterized in that, The preparation method includes: Silicon-based materials and low-carbon residue carbon sources are mixed at a mass ratio of 1:0.1 to 1:10, then a solvent is added and stirred until the low-carbon residue carbon source is dissolved. After ultrasonic treatment, spray granulation is performed to obtain spray particles with an average particle size of 1 nm to 30 μm. A compound containing boron and / or calcium is mixed with a high carbon residue polymer and ball-milled to obtain ball-milled particles with an average particle size of 1 nm to 500 nm; the compound containing boron and / or calcium includes one or more of boron oxide, calcium oxide, and calcium hydroxide. After the sprayed particles and the ball-milled particles are mixed evenly at a mass ratio of 1:1 to 20:1, the mixture is heated to 700°C to 1200°C at a rate of 1°C / min to 10°C / min under a protective atmosphere and kept at that temperature for 1 hour to 15 hours. The product is then broken up and sieved to obtain composite material particles with an average particle size of 1μm to 100μm. The composite material particles were added to distilled water and stirred, then filtered and dried to obtain the silicon-carbon anode material with an in-situ grown onion carbon layer structure. The silicon-carbon anode material includes a core and a shell; The core is a composite sphere of silicon-based material and carbon material, and the particle size of the composite sphere ranges from 1μm to 50μm; wherein, the raw material of the carbon material is a low-carbon residue carbon source, and the core has pores formed after the low-carbon residue carbon source is carbonized; The outer shell is an in-situ grown onion carbon layer structure with a thickness of 1 nm to 1000 nm. The particle size range of the silicon-carbon anode material is 1 μm to 100 μm.
2. The preparation method according to claim 1, characterized in that, The mass ratio of the solid to the solvent after adding the silicon-based material and the low-carbon carbon source to the solvent is 1:100 to 1:1000.
3. The preparation method according to claim 1, characterized in that, The silicon-based material includes one or more of silicon, silicon suboxide, modified silicon suboxide, or amorphous silicon alloy; The low-carbon-residue carbon source has a carbon residue rate of ≤20% at 900℃, and specifically includes one or more of glucose, sucrose, polyvinylpyrrolidone or sodium carboxymethyl cellulose. The high carbon residue polymer includes one or more of asphalt, phenolic resin, or epoxy resin.
4. The preparation method according to claim 1, characterized in that, The spray granulation specifically refers to spray granulation using a spray dryer.
5. The preparation method according to claim 1, characterized in that, The stirring time is 1 to 20 hours, and the stirring speed is 500 to 2000 r / min.
6. A negative electrode, characterized in that, The negative electrode comprises a silicon-carbon negative electrode material with an in-situ grown onion carbon layer structure prepared by any of the preparation methods described in claims 1-5.
7. A lithium battery, characterized in that, The lithium battery includes the negative electrode as described in claim 6.