Method for preparing high-capacity hard carbon composite material, hard carbon composite material and application thereof

Abstract

The present invention discloses a preparation method of a high-capacity hard carbon composite material, the hard carbon composite material and an application thereof. The preparation method includes: dissolving a soluble silicon-containing compound in water to prepare a solution with a mass concentration of 1% to 20%; adding a high-molecular polymer containing exchange groups, stirring at 100 rpm to 600 rpm until ion exchange is completed, and then performing filtration and washing to obtain a high-molecular polymer with silicon-containing groups; heating to 700 °C to 900 °C in a protective atmosphere environment and holding for 5 hours to 20 hours to obtain a hard carbon composite material containing nano-silica; after pre-electrolyzing the molten salt in the crucible, connecting the conductive wire connected to the negative electrode of the molten salt electrolysis electrode to the hard carbon composite material containing nano-silica, with the positive electrode in the crucible, continuously heating at a heating rate of 1-10 °C / min to 900-1000 °C, and performing molten salt electrolysis to obtain the high-capacity hard carbon composite material through molten salt electrolysis.

Description

Technical Field

[0001] The present invention relates to the technical field of new energy materials, and particularly relates to a preparation method of a high-capacity hard carbon composite material, a hard carbon composite material and an application thereof. Background Art

[0002] At present, with the vigorous development of lithium-ion batteries, the existing main anode material, graphite, has been difficult to meet people's requirements for battery capacity. Developing high-capacity anode materials has become a top priority.

[0003] The theoretical specific capacity of silicon materials reaches 4200 mAh / g and the source is wide. However, silicon materials have a huge volume effect during the process of lithium insertion and extraction, expand and pulverize during charge and discharge, resulting in a decline in the battery cycle performance. Currently, the modification work on silicon-based materials is continuously carried out. It is found that, as described in the literature (X.H. Liu, L. Zhong, S.H. Huang, S.X. Mao, T. Zhu, J.Y. Huang, Size-Dependent Fracture of Silicon Nanoparticles During Lithiation, ACS Nano, 6(2012)1522-1531), Liu et al. proved through in-situ TEM that silicon materials have a critical size. When the silicon particles exceed the critical size (about 150 nm), cracks can be observed during the lithium insertion process. After that, nano-sized silicon materials have become an important development direction for silicon-based anode materials. However, due to the agglomeration of nanoparticles, the first-cycle Coulomb efficiency of nano-silicon materials will be reduced.

[0004] Silicon monoxide SiOx further developed on the basis of pure silicon materials, although it has a smaller volume expansion and also has a relatively high theoretical capacity, still has problems commonly existing in silicon-based materials, such as poor conductivity and large volume effect during the process of lithium insertion and extraction.

[0005] Therefore, improving silicon-based composite materials and enhancing the cycle stability have become an important development direction for the anode materials of lithium-ion batteries at present. Summary of the Invention

[0006] The object of the present invention is to address the deficiencies of the prior art and provide a preparation method of a high-capacity hard carbon composite material, a hard carbon composite material and an application thereof. The preparation method of the present invention has simple preparation equipment, low raw material cost, good repeatability and easy operation. In the prepared hard carbon composite material, the dispersion of nano-SiOx particles and nano-pores is uniform; and the sintering temperature of the preparation process of the present invention is relatively low, reducing the raw material and production costs. At the same time, the pores existing around the nano-silicon particles can provide a buffer space for the volume expansion of SiOx particles, ensuring the structural stability during the process of lithium insertion and extraction and ensuring a relatively high cycle stability. This material can be used as the anode material of lithium batteries or other fields.

[0007] In view of this, in a first aspect, an embodiment of the present invention provides a method for preparing a high-capacity hard carbon composite material, comprising:

[0008] Dissolving a soluble silicon-containing compound in water to prepare a solution with a mass concentration of 1% to 20%;

[0009] Adding a high molecular polymer containing an exchange group to the solution, stirring the solution at a speed of 100 rpm to 600 rpm until the ion exchange is completed, filtering and washing the solution, and drying the filtered product to obtain a high molecular polymer containing a silicon group;

[0010] The high molecular polymer having silicon-containing groups is heated to 700° C. to 900° C. at a heating rate of 0.5° C. / min to 5° C. / min in a protective atmosphere, and kept at this temperature for 5 to 20 hours to obtain a hard carbon composite material containing nano-silicon dioxide;

[0011] Put the dried halide salt into a crucible, and respectively wrap two graphite sheets with conductive wires and suspend them on the crucible as the positive electrode and the negative electrode for electrolysis; introduce argon gas with a gas flow rate of 0.5-2L / min, and heat the temperature to 800-900°C at a rate of 2-10°C / min, and place the two graphite sheets after keeping the temperature for half an hour; apply a constant voltage of 2.5-3.0V between the two graphite sheets for pre-electrolysis, and the pre-electrolysis time is 1-2 hours;

[0012] After the pre-electrolysis is completed, the graphite sheet connected to the negative electrode is lifted up from the molten salt to be suspended in the air, and the conductive wire connected to the negative electrode is connected to the hard carbon composite material containing nano-silicon dioxide, and the positive electrode is kept in the crucible; the temperature is continued to be increased to 900-1000°C at a heating rate of 1-10°C / min; a constant voltage of 2.2-3.0V is applied between the positive and negative electrodes of the molten salt electrolysis electrode, and electrolysis is started for 5-20 hours; after the electrolysis is completed, the high-capacity hard carbon composite material is obtained; wherein, nano-SiOx particles and nano-pores are uniformly dispersed inside the high-capacity hard carbon composite material; the nano-pores exist around the nano-SiOx particles; 0≤X<2.

[0013] Preferably, the exchange group includes one or more of a sulfonic acid group (-SO3H), a carboxyl group (-COOH), and a quaternary amine group (-NR3OH).

[0014] Preferably, the molar ratio of silicon in the soluble silicon-containing compound to the exchange groups in the high molecular polymer containing exchange groups is 0.1:1 to 1:1.

[0015] Preferably, the time for fully stirring to complete the ion exchange is 24 hours to 48 hours.

[0016] Preferably, the polymer includes one or a combination of several of polystyrene, epoxy resin, urea-formaldehyde resin, acrylic resin, and polyethylene oxide;

[0017] The soluble silicon-containing compound includes sodium silicate and / or potassium silicate;

[0018] The halogen salt includes one or a combination of several of calcium chloride, magnesium chloride, sodium chloride, or potassium chloride;

[0019] The protective atmosphere is a nitrogen atmosphere or an argon atmosphere.

[0020] Preferably, the conductive wire is one of molybdenum wire, copper wire, or iron wire, and the diameter is 0.2 mm to 1 mm.

[0021] In a second aspect, an embodiment of the present invention provides a high-capacity hard carbon composite material prepared by the preparation method described in the first aspect above. The high-capacity hard carbon composite material is a hard carbon material in which nano-SiOx particles and nano-pores are uniformly dispersed inside; the nano-pores exist around the nano-SiOx particles; 0 ≤ X < 2;

[0022] The particle size range of the high-capacity hard carbon composite material is 0.1 nm to 100 nm. In the high-capacity hard carbon composite material, the mass content ratio of SiOx is 1% to 80%.

[0023] Preferably, the hard carbon composite material is obtained by carbonizing a silicon-containing group polymer formed by ion exchange of a polymer containing an exchange group and a soluble silicon-containing compound; the exchange group includes one or several of sulfonic acid group (-SO3H), carboxyl group (-COOH), and quaternary amine group (-NR3OH).

[0024] In a third aspect, an embodiment of the present invention provides a negative electrode, and the negative electrode includes the high-capacity hard carbon composite material described in the first aspect above.

[0025] In a fourth aspect, an embodiment of the present invention provides a lithium battery, and the lithium battery includes the negative electrode described in the third aspect above.

[0026] The preparation method of the high-capacity hard carbon composite material provided by the present invention has simple preparation equipment, low raw material cost, good repeatability, and easy operation. In the prepared hard carbon composite material, the dispersion of nano-SiOx particles and nano-pores is uniform; and the sintering temperature of the preparation process of the present invention is relatively low, reducing the raw material and production costs. At the same time, the pores existing around the nano-silicon particles can provide a buffer space for the volume expansion of the SiOx particles, ensuring the structural stability during the process of lithium deintercalation and insertion, and ensuring high cycle stability. This material can be used as a negative electrode material for lithium batteries or other fields. Description of the Drawings

[0027] The technical solution of the embodiment of the present invention is further described in detail below through the drawings and examples.

[0028] Figure 1 A flow chart of a method for preparing a high-capacity hard carbon composite material provided by an embodiment of the present invention;

[0029] Figure 2 A scanning electron microscope (SEM) image of the high-capacity hard carbon composite material provided in Example 1 of the present invention;

[0030] Figure 3 A scanning electron microscope (SEM) image of a cross section of the high-capacity hard carbon composite material provided in Example 1 of the present invention;

[0031] Figure 4 This is a dispersion spectrum (EDS) diagram of Si in the high-capacity hard carbon composite material provided in Example 1 of the present invention;

[0032] Figure 5 The X-ray diffraction (XRD) pattern of Si in the high-capacity hard carbon composite material provided in Example 1 of the present invention;

[0033] Figure 6 It is a comparison diagram of the charging and discharging curves of Example 1, Example 2 and Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0034] The technical scheme of the present invention is further described in detail below through the accompanying drawings and examples. The following examples will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, without departing from the concept of the present invention, several variations and improvements can also be made, which all belong to the protection scope of the present invention.

[0035] Figure 1 The high capacity hard carbon composite material provided by the embodiment of the present invention is Figure 1 The preparation method comprises:

[0036] Step 110, dissolving the soluble silicon-containing compound in water to prepare a solution with a mass concentration of 1% to 20%;

[0037] Specifically, the soluble silicon-containing compound includes sodium silicate and / or potassium silicate.

[0038] Step 120, adding a high molecular polymer containing an exchange group to the solution, stirring the solution at a speed of 100 rpm to 600 rpm until the ion exchange is completed, filtering and washing the solution, and drying the filtered product to obtain a high molecular polymer containing a silicon group;

[0039] Specifically, the exchange groups include one or more of sulfonic acid groups (-SO3H), carboxyl groups (-COOH), and quaternary amine groups (-NR3OH). The high molecular polymers include one or a combination of several of polystyrene, epoxy resin, urea-formaldehyde resin, acrylic resin, and polyethylene oxide.

[0040] The addition amount of the high molecular polymer containing exchange groups is in a molar ratio of 0.1:1 to 1:1 between the silicate radical in the soluble silicon-containing compound and the exchange groups in the high molecular polymer containing exchange groups.

[0041] The time for sufficient stirring until the ion exchange is completed is 24 hours to 48 hours.

[0042] The silicon-containing groups in the high molecular polymer containing silicon-containing groups include silicate radicals in this embodiment. Of course, other silicon-containing groups that can form nano-silicon dioxide after high-temperature processes and are known to those skilled in the art according to common general knowledge are also within the scope of the present invention.

[0043] Step 130: Heat the high molecular polymer containing silicon-containing groups in a protective atmosphere environment at a heating rate of 0.5 °C / min to 5 °C / min to 700 °C to 900 °C, and keep it warm for 5 hours to 20 hours to obtain a hard carbon composite material containing nano-silicon dioxide;

[0044] The protective atmosphere is a nitrogen atmosphere or an argon atmosphere; the reaction device can specifically be a conventional device such as a high-temperature furnace, and no special limitation is made here.

[0045] Step 140: Put the dried halide salt into a crucible, wind two graphite sheets with conductive wires respectively and suspend them above the crucible as the positive and negative electrodes for electrolysis; introduce argon with a gas flow rate of 0.5 - 2 L / min, heat it to 800 - 900 °C at a heating rate of 2 - 10 °C / min, and lower the two graphite sheets after keeping it warm for half an hour; apply a constant voltage of 2.5 - 3.0 V between the two graphite sheets for pre-electrolysis, and the pre-electrolysis time is 1 - 2 hours;

[0046] The pre-electrolysis is mainly to remove impurities in the molten salt. The conductive wire used is one of molybdenum wire, copper wire, or iron wire, with a diameter of 0.2 mm to 1 mm.

[0047] The halide salts used include one or a combination of several of calcium chloride, magnesium chloride, sodium chloride, or potassium chloride.

[0048] Step 150: After the pre-electrolysis is completed, lift the graphite sheet connected to the negative electrode upward from the molten salt to suspend it, and connect the conductive wire connected to the negative electrode to the hard carbon composite material containing nano-silica. Keep the positive electrode in the crucible. Continue to heat up at a heating rate of 1 - 10 °C / min to 900 - 1000 °C. Apply a constant voltage of 2.2 - 3.0 V between the positive and negative electrodes of the molten salt electrolysis electrode to start electrolysis, and the electrolysis time is 5 - 20 hours. After the electrolysis is completed, a high-capacity hard carbon composite material is obtained.

[0049] During the molten salt electrolysis process, the halide salt melts into a liquid phase to provide a reaction medium. A large number of active electrons generated during this process are beneficial for the reaction to proceed at low temperatures. By using a voltage lower than the decomposition potential of the molten salt and higher than the decomposition potential of silicon dioxide, deoxidation occurs at the negative electrode, and oxygen ions lose electrons at the positive electrode, causing the silicon dioxide in the hard carbon composite material containing nano-silica to be reduced. When the reaction time is sufficient for all the oxygen ions in the silicon dioxide to lose electrons, the product obtained is nano-silicon particles.

[0050] Among them, nano-SiOx particles and nano-pores are uniformly dispersed inside the high-capacity hard carbon composite material; the nano-pores exist around the nano-SiOx particles; 0 ≤ X < 2. Preferably, nano-silicon monoxide and Si particles coexist, that is, 0 < X < 2, and X = 0 also coexists.

[0051] The particle size range of the high-capacity hard carbon composite material prepared by the present invention is 0.1 nm to 100 nm. In the high-capacity hard carbon composite material, the mass content ratio of SiOx is 1% to 80%.

[0052] The high-capacity hard carbon composite material prepared by the present invention can be used as the negative electrode material of a lithium-ion battery.

[0053] To better understand the technical solution provided by the present invention, the following uses multiple specific examples to separately illustrate the specific process of preparing the high-capacity hard carbon composite material by applying the method provided in the above embodiments of the present invention, as well as the method and battery characteristics of applying it to a lithium-ion secondary battery.

[0054] Example 1

[0055] This example provides a method for preparing a high-capacity hard carbon composite material, which includes:

[0056] Step 1: Take 200 g of potassium silicate and dissolve it in 1800 ml of water to prepare a solution with a mass concentration of about 10%. Add 289 g of polystyrene containing a carboxyl (-COOH) exchange group (exchange capacity is about 4.5 mmol / g) according to the molar ratio of silicon to the exchange group in the polymer of 1:1. Stir at a speed of 100 r / min for 48 hours until the ion exchange is completed. Then filter and wash the polymer 3 times, and dry it to obtain a polymer containing silicon groups.

[0057] Step 2: Put the dried sample into the reaction device, heat it to 1200 °C at a rate of 0.5 °C / min, and keep it for 5 hours in a nitrogen atmosphere for carbonization to obtain a carbonized polymer material containing nano-silica.

[0058] Step 3: Put 100 g of dried calcium chloride into a crucible, introduce argon with a gas flow rate of 2 L / min, heat it to 900 °C at a heating rate of 10 °C / min, keep it for half an hour, and then place two graphite sheets wound with molybdenum wires with a diameter of 1 mm connected to the positive and negative electrodes respectively and suspended above the crucible. The distance between the positive and negative electrode sheets formed by the two graphite sheets is 6 cm, and a constant voltage of 3.0 V is applied for pre-electrolysis for 2 hours;

[0059] Step 4: After the pre-electrolysis is completed, take out the graphite sheet connected to the negative electrode, connect the conductive wire connected to the negative electrode to the carbonized polymer material containing nano-silica obtained in Step 2, and keep the positive electrode in the crucible; the distance between the two poles is 6 cm, introduce argon with a gas flow rate of 2 L / min, heat it to 1000 °C at a heating rate of 10 °C / min, apply a constant voltage of 3.0 V between the two poles, and start electrolysis for 20 hours. After cooling, the high-capacity hard carbon composite material is obtained.

[0060] The high-capacity hard carbon composite material obtained in this example was subjected to SEM and EDS tests. Figure 2 This is the SEM image of the high-capacity hard carbon composite material provided in Example 1 of the present invention. Figure 3 This is the SEM image of the cross-section of the high-capacity hard carbon composite material; it can be seen that the dispersion of nano-SiOx particles and nano-pores in the hard carbon composite material is uniform. The present invention solves the problems of uneven dispersion and nano-agglomeration existing in the preparation process of the current carbon-based composite material containing nano-silicon; there are pores constructed around the nano-SiOx particles, which can provide a buffer space for the volume expansion of silicon particles and ensure the structural stability during the process of lithium deintercalation and insertion. Figure 4 This is the EDS image, and it can be seen that the silicon element is evenly distributed in the material, indicating that the SiOx itself is evenly dispersed. Figure 5 This is the XRD image of Si in the high-capacity hard carbon composite material provided in Example 1 of the present invention. It can be seen that in addition to amorphous silicon suboxide particles, there are also some SiOx (X = 0) particles, showing certain characteristic peaks.

[0061] Example 2

[0062] This example provides a preparation method of a high-capacity hard carbon composite material, which includes:

[0063] Step 1: Take 200 g of potassium silicate and dissolve it in 6500 ml of water to prepare a solution with a mass concentration of approximately 3%. Add 2890 g of polystyrene with a carboxyl group (-COOH) exchange group (exchange capacity of approximately 4.5 mmol / g) according to the molar ratio of silicon to the exchange group in the polymer of 0.1:1. Stir thoroughly at a speed of 100 r / min for 24 hours until the ion exchange is completed. Then filter and wash the polymer three times, and dry it to obtain a silicon group-containing polymer.

[0064] Step 2: Put the dried sample into a reaction device, heat it to 900 °C at a rate of 2 °C / min, and keep it at this temperature for 20 hours in an argon atmosphere for carbonization to obtain a carbonized polymer material containing nano-silica.

[0065] Step 3: Put 100 g of dried calcium chloride into a crucible, introduce argon with a gas flow rate of 0.5 L / min, heat it to 800 °C at a heating rate of 10 °C / min, keep it at this temperature for half an hour, and then place two graphite sheets wound with copper wires with a diameter of 1 mm connected to the positive and negative electrodes respectively and suspended above the crucible. The distance between the positive and negative electrode sheets formed by the two graphite sheets is 2 cm, and a constant voltage of 3.0 V is applied for pre-electrolysis for 2 hours.

[0066] Step 4: After the pre-electrolysis is completed, take out the graphite sheet connected to the negative electrode, connect the conductive wire connected to the negative electrode to the hard carbon composite material of nano-silica obtained in Step 2. The distance between the two electrodes is 2 cm, introduce argon with a gas flow rate of 0.5 L / min, heat it to 1000 °C at a heating rate of 1 °C / min, apply a constant voltage of 2.5 V between the two electrodes, and start electrolysis for 5 hours. After cooling, the high-capacity hard carbon composite material is obtained.

[0067] Example 3

[0068] This example provides a method for preparing a high-capacity hard carbon composite material, which includes:

[0069] Step 1: Take 200 g of sodium silicate and dissolve it in 800 ml of water to prepare a solution with a mass concentration of approximately 20%. Add 380 g of polystyrene with a carboxyl group (-COOH) exchange group (exchange capacity of approximately 4.5 mmol / g) according to the molar ratio of silicon to the exchange group in the polymer of 1:1. Stir thoroughly at a speed of 100 r / min for 24 hours until the ion exchange is completed. Then filter and wash the polymer three times, and dry it to obtain a silicon group-containing polymer.

[0070] Step 2: Put the dried sample into a reaction device, heat it to 1000 °C at a rate of 2 °C / min, and keep it at this temperature for 10 hours in a nitrogen atmosphere for carbonization to obtain a carbonized polymer material containing nano-silica.

[0071] Step 3: Put 100 g of dried calcium chloride into a crucible, introduce argon with a gas flow rate of 2 L / min, and raise the temperature to 900 °C at a heating rate of 10 °C / min. After holding for half an hour, place two graphite sheets wound with iron wires with a diameter of 1 mm respectively connected to the positive and negative electrodes and suspended above the crucible. The distance between the positive and negative electrode sheets formed by the two graphite sheets is 4 cm, and a constant voltage of 2.8 V is applied for pre-electrolysis, and the pre-electrolysis time is 1 hour;

[0072] Step 4: After the pre-electrolysis is completed, take out the graphite sheet connected to the negative electrode, connect the conductive wire connected to the negative electrode to the hard carbon composite material of nano-silica obtained in Step 2. The distance between the two electrodes is 4 cm, introduce argon with a gas flow rate of 2 L / min, and raise the temperature to 1000 °C at a heating rate of 10 °C / min. Apply a constant voltage of 3.0 V between the two electrodes to start electrolysis, and the electrolysis time is 20 hours. After cooling, the high-capacity hard carbon composite material is obtained.

[0073] Example 4

[0074] This example provides a method for preparing a high-capacity hard carbon composite material, which includes:

[0075] Step 1: Take 200 g of sodium silicate and dissolve it in 1800 ml of water to prepare a solution with a mass concentration of about 10%. Add 1445 g of polystyrene containing carboxyl (-COOH) exchange groups (exchange capacity is about 4.5 mmol / g) according to the molar ratio of silicon to the exchange groups in the polymer of 0.5:1. Stir at a speed of 100 r / min for 12 hours until the ion exchange is completed. Then filter and wash the polymer 3 times, and after drying, a silicon-containing group polymer is obtained.

[0076] Step 2: Put the dried sample into a reaction device, raise the temperature to 900 °C at a rate of 5 °C / min, and hold for 15 hours in a nitrogen atmosphere for carbonization to obtain a carbonized polymer material containing nano-silica.

[0077] Step 3: Put 100 g of dried calcium chloride into a crucible, introduce argon with a gas flow rate of 2 L / min, and raise the temperature to 900 °C at a heating rate of 10 °C / min. After holding for half an hour, place two graphite sheets wound with iron wires with a diameter of 1 mm respectively connected to the positive and negative electrodes and suspended above the crucible. The distance between the positive and negative electrode sheets formed by the two graphite sheets is 6 cm, and a constant voltage of 3.0 V is applied for pre-electrolysis, and the pre-electrolysis time is 2 hours;

[0078] Step 4: After the pre-electrolysis is completed, the graphite sheet connected to the negative electrode is taken out, and the conductive wire connected to the negative electrode is connected to the hard carbon composite material of nano-silicon dioxide obtained in step 2. The distance between the two electrodes is 6 cm. Argon gas is introduced at a gas flow rate of 2L / min. The temperature is increased to 950°C at a heating rate of 5°C / min. A constant voltage of 3.0V is applied between the two electrodes to start electrolysis. The electrolysis time is 20 hours. After cooling, the high-capacity hard carbon composite material is obtained.

[0079] Example 5

[0080] This embodiment provides a method for preparing a high-capacity hard carbon composite material, comprising:

[0081] Step 1: Take 200g of sodium silicate and add 1800ml of water to dissolve it to prepare a solution with a mass concentration of about 10%, add 468g of polystyrene containing quaternary amino group (-NR3OH) exchange group (exchange capacity is about 3.5mmol / g) according to the molar ratio of silicon to exchange group in the polymer of 1:1, stir at a speed of 100r / min for 24 hours until the ion exchange is completed, filter and wash the polymer for 3 times, and obtain the silicon group-containing polymer after drying.

[0082] Step 2: Place the dried sample into a reaction device, heat it to 1000° C. at a rate of 5° C. / min, and carbonize it under a nitrogen atmosphere for 15 hours to obtain a carbonized polymer material containing nano-silicon oxide.

[0083] Step 3: Place 100g of dried calcium chloride in a crucible, introduce argon gas at a gas flow rate of 2L / min, and heat to 900℃ at a rate of 10℃ / min. After keeping warm for half an hour, place two graphite sheets wrapped with iron wires of 1mm in diameter connected to the positive and negative electrodes and suspended on the crucible. The distance between the positive and negative electrodes formed by the two graphite sheets is 4cm, and a constant voltage of 3.0V is applied for pre-electrolysis. The pre-electrolysis time is 2 hours;

[0084] Step 4: After the pre-electrolysis is completed, the graphite sheet connected to the negative electrode is taken out, and the conductive wire connected to the negative electrode is connected to the hard carbon composite material of nano-silicon dioxide obtained in step 2. The distance between the two electrodes is 6 cm. Argon gas is introduced at a gas flow rate of 2L / min. The temperature is raised to 1000°C at a heating rate of 10°C / min. A constant voltage of 3.0V is applied between the two electrodes to start electrolysis. The electrolysis time is 10 hours. After cooling, the high-capacity hard carbon composite material is obtained.

[0085] Example 6

[0086] This embodiment provides a method for preparing a high-capacity hard carbon composite material, comprising:

[0087] Step 1: Take 200 g of sodium silicate, dissolve it in 1800 ml of water to prepare a solution with a mass concentration of about 10%. Add 1311 g of polystyrene containing quaternary amine group (-NR3OH) exchange groups (exchange capacity is about 3.5 mmol / g) according to the molar ratio of silicon to exchange groups in the polymer of 0.7:1. Stir well at a speed of 100 r / min for 24 hours until the ion exchange is completed. Then filter and wash the polymer 3 times, and dry it to obtain a silicon-containing group polymer.

[0088] Step 2: Put the dried sample into a reaction device, heat it to 1000 °C at a rate of 5 °C / min, and keep it for 12 hours in a nitrogen atmosphere for carbonization to obtain a carbonized polymer material containing nano-silica.

[0089] Step 3: Put 100 g of dried potassium chloride into a crucible, pass argon with a gas flow rate of 2 L / min, heat it to 900 °C at a heating rate of 10 °C / min, keep it for half an hour, and then put down two graphite sheets wound with molybdenum wires with a diameter of 0.2 mm connected to the positive and negative electrodes respectively and suspended above the crucible. The distance between the positive and negative electrode sheets formed by the two graphite sheets is 6 cm, and a constant voltage of 3.0 V is applied for pre-electrolysis for 2 hours.

[0090] Step 4: After the pre-electrolysis is completed, take out the graphite sheet connected to the negative electrode, connect the conductive wire connected to the negative electrode to the hard carbon composite material of nano-silica obtained in Step 2. The distance between the two electrodes is 6 cm, pass argon with a gas flow rate of 2 L / min, heat it to 1000 °C at a heating rate of 10 °C / min, apply a constant voltage of 3.0 V between the two electrodes, and start electrolysis for 20 hours. After cooling, the high-capacity hard carbon composite material is obtained.

[0091] Example 7

[0092] This example provides a method for preparing a high-capacity hard carbon composite material, which includes:

[0093] Step 1: Take 200 g of sodium silicate, dissolve it in 1800 ml of water to prepare a solution with a mass concentration of about 10%. Add 936 g of polystyrene containing quaternary amine group (-NR3OH) exchange groups (exchange capacity is about 3.5 mmol / g) according to the molar ratio of silicon to exchange groups in the polymer of 0.5:1. Stir well at a speed of 100 r / min for 24 hours until the ion exchange is completed. Then filter and wash the polymer 3 times, and dry it to obtain a silicon-containing group polymer.

[0094] Step 2: Put the dried sample into a reaction device, heat it to 1000 °C at a rate of 5 °C / min, and keep it at this temperature for 10 hours in a nitrogen atmosphere for carbonization to obtain a carbonized polymer material containing nano-silica.

[0095] Step 3: Put 100 g of dried sodium chloride into a crucible, introduce argon with a gas flow rate of 2 L / min, heat it to 900 °C at a heating rate of 10 °C / min, keep it at this temperature for half an hour, and then place two graphite sheets wound with copper wires with a diameter of 0.2 mm connected to the positive and negative electrodes respectively and suspended above the crucible. The distance between the positive and negative electrode sheets formed by the two graphite sheets is 4 cm, and a constant voltage of 3.0 V is applied for pre-electrolysis for 2 hours.

[0096] Step 4: After the pre-electrolysis is completed, take out the graphite sheet connected to the negative electrode, connect the conductive wire connected to the negative electrode to the hard carbon composite material of nano-silica obtained in Step 2, the distance between the two electrodes is 6 cm, introduce argon with a gas flow rate of 2 L / min, heat it to 1000 °C at a heating rate of 10 °C / min, apply a constant voltage of 3.0 V between the two electrodes, start electrolysis for 10 hours, and obtain the high-capacity hard carbon composite material after cooling.

[0097] Example 8

[0098] This example provides a method for preparing a high-capacity hard carbon composite material, which includes:

[0099] Step 1: Take 200 g of potassium silicate, add 1800 ml of water to dissolve it to prepare a solution with a mass concentration of about 10%, add 3716 g of polystyrene containing quaternary ammonium group (-NR3OH) exchange groups (exchange capacity is about 3.5 mmol / g) according to the molar ratio of silicon to the exchange groups in the polymer of 0.1:1, stir it at a speed of 100 r / min for 24 hours until the ion exchange is completed, filter and wash the polymer 3 times, and obtain a silicon-containing group polymer after drying.

[0100] Step 2: Put the dried sample into a reaction device, heat it to 950 °C at a rate of 5 °C / min, and keep it at this temperature for 10 hours in a nitrogen atmosphere for carbonization to obtain a carbonized polymer material containing nano-silica.

[0101] Step 3: Put 100 g of dried sodium chloride into a crucible, introduce argon with a gas flow rate of 2 L / min, heat it to 900 °C at a heating rate of 10 °C / min, keep it at this temperature for half an hour, and then place two graphite sheets wound with copper wires with a diameter of 0.2 mm connected to the positive and negative electrodes respectively and suspended above the crucible. The distance between the positive and negative electrode sheets formed by the two graphite sheets is 6 cm, and a constant voltage of 3.0 V is applied for pre-electrolysis for 2 hours.

[0102] Step 4: After the pre-electrolysis is completed, take out the graphite sheet connected to the negative electrode, connect the conductive wire connected to the negative electrode to the hard carbon composite material of nano-silica obtained in Step 2, with a distance of 6 cm between the two electrodes, introduce argon with a gas flow rate of 2 L / min, heat up to 1000 °C at a heating rate of 10 °C / min, apply a constant voltage of 3.0 V between the two electrodes, start electrolysis, and the electrolysis time is 20 hours. After cooling, the high-capacity hard carbon composite material is obtained.

[0103] Example 9

[0104] This example provides a method for preparing a high-capacity hard carbon composite material, which includes:

[0105] Step 1: Take 200 g of potassium silicate and dissolve it in 1800 ml of water to prepare a solution with a mass concentration of about 10%. Add 372 g of polystyrene containing quaternary amine group (-NR3OH) exchange groups (exchange capacity is about 3.5 mmol / g) according to the molar ratio of silicon to exchange groups in the polymer of 1:1. Stir at a speed of 200 r / min for 30 hours until the ion exchange is completed. Then filter and wash the polymer three times, and dry it to obtain the silicon-containing group polymer.

[0106] Step 2: Put the dried sample into the reaction device, heat up to 900 °C at a rate of 5 °C / min, and keep it at this temperature for 15 hours in a nitrogen atmosphere for carbonization to obtain a carbonized polymer material containing nano-silica.

[0107] Step 3: Put 100 g of dried potassium chloride into the crucible, introduce argon with a gas flow rate of 2 L / min, heat up to 900 °C at a heating rate of 10 °C / min, keep it at this temperature for half an hour, and then put down two graphite sheets wound by molybdenum wires with a diameter of 1 mm respectively connected to the positive and negative electrodes and suspended above the crucible. The distance between the positive and negative electrode plates formed by the two graphite sheets is 6 cm, and a constant voltage of 3.0 V is applied for pre-electrolysis, and the pre-electrolysis time is 2 hours;

[0108] Step 4: After the pre-electrolysis is completed, take out the graphite sheet connected to the negative electrode, connect the conductive wire connected to the negative electrode to the hard carbon composite material of nano-silica obtained in Step 2, with a distance of 6 cm between the two electrodes, introduce argon with a gas flow rate of 2 L / min, heat up to 1000 °C at a heating rate of 5 °C / min, apply a constant voltage of 3.0 V between the two electrodes, start electrolysis, and the electrolysis time is 20 hours. After cooling, the high-capacity hard carbon composite material is obtained.

[0109] Example 10

[0110] This example provides a method for preparing a high-capacity hard carbon composite material, which includes:

[0111] Step 1: Take 200 g of potassium silicate and dissolve it in 1800 ml of water to prepare a solution with a mass concentration of about 10%. Add 743 g of polystyrene containing quaternary amino group (-NR3OH) exchange groups (exchange capacity is about 3.5 mmol / g) according to the molar ratio of silicon to exchange groups in the polymer of 0.5:1. Stir thoroughly at a speed of 100 r / min for 24 hours until the ion exchange is completed. Then filter and wash the polymer three times, and dry it to obtain a silicon-containing group polymer.

[0112] Step 2: Put the dried sample into a reaction device, heat it to 950 °C at a rate of 3 °C / min, and keep it at this temperature for 10 hours in a nitrogen atmosphere for carbonization to obtain a carbonized polymer material containing nano-silica.

[0113] Step 3: Put 100 g of dried magnesium chloride into a crucible, introduce argon with a gas flow rate of 2 L / min, heat it to 900 °C at a heating rate of 10 °C / min, keep it at this temperature for half an hour, and then put down two graphite sheets wound with molybdenum wires with a diameter of 0.2 mm connected to the positive and negative electrodes respectively and suspended above the crucible. The distance between the positive and negative electrode sheets formed by the two graphite sheets is 6 cm, and a constant voltage of 3.0 V is applied for pre-electrolysis for 2 hours.

[0114] Step 4: After the pre-electrolysis is completed, take out the graphite sheet connected to the negative electrode, connect the conductive wire connected to the negative electrode to the hard carbon composite material of nano-silica obtained in Step 2. The distance between the two electrodes is 6 cm, introduce argon with a gas flow rate of 2 L / min, heat it to 1000 °C at a heating rate of 10 °C / min, apply a constant voltage of 3.0 V between the two electrodes, and start electrolysis for 20 hours. After cooling, the high-capacity hard carbon composite material is obtained.

[0115] To better illustrate the properties of the high-capacity hard carbon composite material of the present invention, Comparative Example 1 is used for comparison.

[0116] Comparative Example 1

[0117] This comparative example provides a preparation method of a common nano-silicon-carbon composite material, including:

[0118] Step 1: Take 200 g of nano-SiOx (X = 1) and 500 g of polystyrene powder, mix them and put them into a reaction device, heat it to 1200 °C at a rate of 0.5 °C / min, and keep it at this temperature for 5 hours in a nitrogen atmosphere for carbonization.

[0119] Step 2: Put the sample obtained above into a reaction device, heat it to 1000 °C at a rate of 1 °C / min, and keep it at this temperature for 1 hour to obtain a comparative sample of a hard carbon composite material containing nano-SiOx with uniform internal structure.

[0120] To test the electrochemical properties of the materials prepared in each example, the obtained hard carbon composite material was used as the negative electrode material and uniformly mixed with 2% carbon black, 2% sodium carboxymethyl cellulose, and 3% styrene-butadiene rubber based on the total mass (excluding the solvent) in a polyvinylidene fluoride (PVDF) solvent to form a battery slurry. The slurry was coated on a copper foil, dried, and cut into circular pieces with a diameter of 14 mm. After vacuum drying at 100 °C for 12 hours, a lithium metal was used as the counter electrode in a glove box containing a high-purity Ar atmosphere, and a solution of 1 mol LiPF6 (ethylene carbonate (EC) / dimethyl carbonate (DMC) v:v = 1:1) was used as the electrolyte to assemble a button cell, and its structure and electrochemical properties were evaluated through testing.

[0121] The constant current charge-discharge mode was used for testing. The discharge cut-off voltage was 0.005 V, and the charge cut-off voltage was 1.5 V. The charge-discharge test was carried out at a current density of C / 10. The results were recorded in Table 1.

[0122]

[0123] Table 1

[0124] As can be seen from Table 1, the high-capacity hard carbon composite material proposed in the present invention has a relatively high initial charge specific capacity and initial cycle efficiency. By uniformly dispersing nano-SiOx particles and nano-pores inside, the reversible specific capacity of the material is improved compared with the existing commercial hard carbon materials. The preparation method proposed in the present invention has the characteristics of simple equipment, low raw material cost, good repeatability, and easy operation.

[0125] Figure 6 This is a comparison chart of the charge-discharge curves of the button cells of Example 1, Example 2 and Comparative Example 1 of the present invention. It can be seen that compared with Comparative Example 1, the high-capacity hard carbon composite materials of Example 1 and Example 2 can improve the cycle stability.

[0126] The specific embodiments described above have further elaborated on the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above description is only the specific embodiments of the present invention and is not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a high-capacity hard carbon composite material, characterized in that, The preparation method comprises: Dissolving a soluble silicon-containing compound in water to prepare a solution with a mass concentration of 1% to 20%; Adding a high molecular polymer containing an exchange group to the solution, stirring the solution at a speed of 100 rpm to 600 rpm until the ion exchange is completed, filtering and washing the solution, and drying the filtered product to obtain a high molecular polymer containing a silicon group; The high molecular polymer having silicon-containing groups is heated to 700° C. to 900° C. at a heating rate of 0.5° C. / min to 5° C. / min in a protective atmosphere, and kept at this temperature for 5 to 20 hours to obtain a hard carbon composite material containing nano-silicon dioxide; Put the dried halide salt into a crucible, and wrap two graphite sheets with conductive wires and suspend them on the crucible as the positive electrode and negative electrode for electrolysis; introduce argon gas with a gas flow rate of 0.5-2 L / min, and heat it to 800-900 ℃ at a rate of 2-10 ℃ / min. After keeping the temperature for half an hour, put down the two graphite sheets; apply a constant voltage of 2.5-3.0 V between the two graphite sheets for pre-electrolysis, and the pre-electrolysis time is 1-2 hours; After the pre-electrolysis is completed, the graphite sheet connected to the negative electrode is lifted up from the molten salt to be suspended in the air, and the conductive wire connected to the negative electrode is connected to the hard carbon composite material containing nano-silicon dioxide, and the positive electrode is kept in the crucible; the temperature is continued to be increased to 900-1000°C at a heating rate of 1-10°C / min; a constant voltage of 2.2-3.0 V is applied between the positive and negative electrodes of the molten salt electrolysis electrode, and electrolysis is started for 5-20 hours; after the electrolysis is completed, the high-capacity hard carbon composite material is obtained; wherein, nano-SiOx particles and nano-pores are uniformly dispersed inside the high-capacity hard carbon composite material; the nano-pores exist around the nano-SiOx particles; 0≤X<2.

2. The method for preparing a high-capacity hard carbon composite material according to claim 1, characterized in that, The exchange group includes one or more of a sulfonic acid group (-SO3H), a carboxyl group (-COOH), and a quaternary amine group (-NR3OH).

3. The method for preparing a high-capacity hard carbon composite material according to claim 1, characterized in that, The molar ratio of silicon in the soluble silicon-containing compound to the exchange groups in the high molecular polymer containing exchange groups is 0.1:1 to 1:

1.

4. The method for preparing a high-capacity hard carbon composite material according to claim 1, characterized in that, The time for fully stirring to complete the ion exchange is 24 hours to 48 hours.

5. The method for preparing a high-capacity hard carbon composite material according to claim 1, characterized in that, The high molecular polymer includes: one or a combination of polystyrene, epoxy resin, urea-formaldehyde resin, acrylic resin, and polyoxyethylene; The soluble silicon-containing compound includes: sodium silicate and / or potassium silicate; The halide salt includes a combination of one or more of calcium chloride, magnesium chloride, sodium chloride or potassium chloride; The protective atmosphere is a nitrogen atmosphere or an argon atmosphere.

6. The method for preparing a high-capacity hard carbon composite material according to claim 1, characterized in that, The conductive wire is one of molybdenum wire, copper wire or iron wire, and has a diameter of 0.2 mm to 1 mm.

7. A high-capacity hard carbon composite material prepared by the preparation method according to any one of claims 1-6, characterized in that, The high-capacity hard carbon composite material is a hard carbon material in which nano-SiOx particles and nano-pores are uniformly dispersed; the nano-pores exist around the nano-SiOx particles; 0≤X<2; The particle size range of the high-capacity hard carbon composite material is from 0.1 nm to 100 nm. In the high-capacity hard carbon composite material, the mass content ratio of SiOx is 1% to 80%.

8. The high-capacity hard carbon composite material according to claim 7 above, characterized in that, The hard carbon composite material is formed by carbonizing a silicon group-containing polymer formed by ion exchange between a polymer with exchange groups and a soluble silicon compound; the exchange groups include one or more of a sulfonic acid group (-SO3H), a carboxyl group (-COOH), and a quaternary amine group (-NR3OH).

9. A negative electrode, characterized in that, The negative electrode includes the high-capacity hard carbon composite material prepared by the preparation method according to any one of claims 1 to 6 above.

10. A lithium battery, characterized in that, The lithium battery includes the negative electrode according to claim 9 above.

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