A silicon-copper negative electrode material, its preparation method and use

Abstract

The present invention belongs to the field of batteries. The present invention provides a silicon-copper negative electrode material, a preparation method thereof and uses thereof. In the preparation method, a silicon raw material, a reducing agent and a cuprous compound are uniformly mixed, first melting is carried out, after cooling, it is broken and ground, then second melting is carried out, and then the temperature is lowered to an insulation temperature for insulation growth to obtain the silicon-copper negative electrode material; the silicon-copper negative electrode material obtained by the high-temperature solid-phase melting method is silicon-doped nano-copper, which can be directly formed into a negative electrode after the second melting and directly serve as the negative electrode of a lithium battery without the need to additionally use a negative electrode current collector and without negative electrode processes such as pulping and coating, greatly simplifying the manufacturing process of the negative electrode and effectively reducing the cost. The obtained silicon-copper negative electrode material has a high capacity and a low resistance, effectively improving the charge exchange process in the battery.

Description

Technical Field

[0001] The present invention belongs to the field of batteries, and relates to a silicon-copper negative electrode material, a preparation method thereof, and uses thereof. Background Art

[0002] At present, lithium-ion batteries are all made by coating the positive electrode active material lithium iron phosphate and the negative electrode active material graphite on copper-aluminum foils to form positive and negative electrode sheets, and then making lithium-ion batteries by the method of stacking the positive electrode - separator - negative electrode. This manufacturing method requires cumbersome processes such as pulping and coating to manufacture the positive and negative electrode sheets, and the resulting batteries have high costs and low energy densities. Therefore, proposing a new structural scheme and construction method has become a new development direction for battery manufacturing. Among them, the scheme of using silicon-based materials to form an integrated negative electrode has received extensive attention.

[0003] According to research, silicon has become one of the most promising negative electrode materials in solid-state batteries (SSBs) due to its high specific capacity characteristics (3590 mAh·g -1 ). Silicon can not only prevent lithium electroplating and lithium dendrite growth at a lithiation potential of 0.4 V (vs Li + / Li), but also has a higher energy density than other alloy negative electrodes. In addition, silicon negative electrodes have high abundance, low cost, and environmental friendliness.

[0004] However, silicon-based negative electrode materials also have three problems that limit their large-scale development and application: First, the cyclic volume expansion is serious, about 300%, which is 20 times that of the graphite negative electrode. During the volume expansion process, silicon itself will be broken or pulverized. Secondly, during the expansion process, the surrounding materials will be squeezed and shrunk, and it is easy to lose electrical contact with the current collector, resulting in a decrease in capacity. Second, the silicon-based material has poor electrical conductivity, and the intrinsic conductivity of silicon is small (2.52×10 -4 / (mΩ)), resulting in a high internal resistance of the battery, further affecting the cycle life. At the same time, it will also restrict the migration of lithium ions, resulting in a decline in the rate performance of the material. Third, the initial Coulomb efficiency of the silicon-based negative electrode material is too low, further deteriorating the cycle / rate performance.

[0005] Therefore, while developing integrated negative electrodes, researchers need to further optimize silicon-based negative electrodes:

[0006] CN112271297A discloses a grid-type laminated structure material synthesis and molding integrated silicon negative electrode. By using an organometallic salt precursor and a spinning polymer, silicon particles are electrospun on a copper foil. After calcination, the integrated silicon negative electrode has a special grid-type laminated fiber structure that can improve the battery capacity, has good flexibility, can provide enough space for expansion, and at the same time increases the specific surface area, improves the wettability, and improves the cycle performance;

[0007] CN115394956A discloses an integrated anode material composed of a 3D current collector - carbon layer - silicon layer. A carbon buffer layer is deposited on the surface of the 3D current collector (such as copper foam, nickel foam, etc.) by magnetron sputtering, and then silicon and carbon layers are deposited alternately in layers. Finally, a carbon protective layer is deposited on the surface of the material. The carbon layer is used as a buffer layer to prevent the active material from directly contacting the electrolyte, and at the same time improve the conductivity of the silicon-based anode. The silicon layer serves as the active material to provide a high specific capacity for the material. The 3D current collector provides a shorter Li+ migration channel while relieving the internal stress during the charge and discharge process. In addition, there is no need to add additional conductive agents and binders, and it can be directly used as the anode material;

[0008] CN109659499A discloses a preparation method for the anode of a silicon-copper lithium-ion battery. A precipitation slurry is obtained by co-precipitation with copper oxalate salt, and then coated on a current collector and dried and sintered to obtain a silicon-copper integrated electrode. The excellent ductility and conductivity of in-situ grown nano-copper using copper oxalate relieve the large volume expansion and poor conductivity of nano-silicon powder;

[0009] In the above three solutions, a current collector is used in the integrated preparation process or there is still a process of coating on a current collector, and the obtained anode material cannot be directly used as the anode. Therefore, it is necessary to develop a new technical solution to optimize and fully integrate the silicon-based anode material, thereby solving the problems of low energy density of lithium batteries, large anode sheet resistance, and high battery manufacturing cost caused by the existing coating manufacturing process. Summary of the Invention

[0010] In view of the problems existing in the prior art, the purpose of the present invention is to provide a silicon-copper anode material, its preparation method and use. The preparation method mixes silicon raw materials, reducing agents and cuprous compounds evenly, performs the first melting, cools and then breaks and grinds, and then performs the second melting. After that, the temperature is lowered to the holding temperature for holding growth to obtain the silicon-copper anode material; the silicon-copper anode material obtained by the high-temperature solid-phase melting method is silicon-doped nano-copper, which can be directly formed into an anode after the second melting and directly serve as the anode of a lithium battery without the need to use an additional anode current collector or processes such as pulping and coating, greatly simplifying the manufacturing process of the anode and effectively reducing the cost. The obtained silicon-copper anode material has a high capacity and low resistance, effectively improving the charge exchange process in the battery.

[0011] To achieve this purpose, the present invention adopts the following technical solutions:

[0012] In the first aspect, the present invention provides a preparation method for a silicon-copper anode material, including the following steps:

[0013] Mix the silicon raw material, reducing agent and cuprous compound evenly, conduct the first melting, cool it and then conduct the second melting, and then reduce the temperature to the heat preservation temperature for heat preservation growth to obtain the silicon-copper negative electrode material.

[0014] The present invention develops a silicon-doped nano-copper material, which can directly serve as the negative electrode of a lithium battery. At the same time, it does not require a negative electrode coating process and does not require the use of copper as the negative electrode current collector, thereby improving the mass energy density of the material. Nano-copper doping can improve the conductivity of the material and reduce the film resistance. The existence of nano-copper in the form of being embedded in silicon can also inhibit the expansion of the silicon negative electrode material. In the preparation method, during the first melting, due to its strong reducibility, the reducing agent will reduce the copper ions in the cuprous compound to elemental copper and uniformly melt it in silicon. At this time, nano-copper has not yet formed, and at the same time, other elements in the cuprous compound, such as halogen, nitrogen, carbon, etc., volatilize at high temperature; when the second melting time is too long, it will affect the heat preservation growth process, inhibit the nucleation and crystallization of nano-copper, resulting in poor growth effect; after the first melting and the second melting, at an appropriate heat preservation temperature and time, the copper in silicon gradually forms copper nanoparticles and grows, obtaining the silicon-copper negative electrode material.

[0015] The following are the preferred technical solutions of the present invention, but not the limitations of the technical solutions provided by the present invention. Through the following technical solutions, the technical purposes and beneficial effects of the present invention can be better achieved and realized.

[0016] As a preferred technical solution of the present invention, the silicon raw material includes silicon wafers and / or silicon powder, preferably silicon powder.

[0017] Preferably, the silicon raw material is ground and sieved before mixing, and the particle size reaches 100-500 mesh.

[0018] When the silicon raw material uses silicon wafers, the cost can be effectively reduced, and silicon powder with finer particle size, such as nano-scale silicon powder, can also be selected according to actual conditions.

[0019] Preferably, the reducing agent includes SiC and / or Si3N4, preferably Si3N4.

[0020] Preferably, the cuprous compound includes any one or a combination of at least two of CuI, CuCl or CuBr. Typical but non-limiting examples of the combination include the combination of CuI and CuCl, the combination of CuCl and CuBr, or the combination of CuBr and CuI, preferably CuI.

[0021] Preferably, the cuprous compound of the present invention is a halogen compound. Although the residue of halogen elements will react with water to form corresponding acids, which will affect the battery safety performance, the preparation method of the present invention can remove halogen elements through the first and second melting and mixing. When using other cuprous compounds, it is impossible to remove excess impurity elements, and it is impossible to crystallize out nano-copper by directly using copper powder. Therefore, cuprous halide compounds are more suitable.

[0022] Preferably, based on the total molar amount of 100%, the molar amount of the silicon raw material is 60% - 90%, such as 60%, 62%, 64%, 66%, 68%, 70%, 72%, 74%, 76%, 78%, 80%, 82%, 84%, 86%, 88% or 90%, etc., but not limited to the listed numbers, and other unlisted numbers within the above numerical range are equally applicable.

[0023] When the amount of the cuprous compound used is excessive, the product is a silicon-copper mixture, and a nano-copper structure embedded in silicon cannot be obtained; when the amount of the cuprous compound used is too small, nucleation and crystallization cannot occur during high-temperature annealing (referring to heat preservation growth), and nano-copper crystals cannot be obtained.

[0024] Preferably, based on the total molar amount of 100%, the molar amount of the reducing agent is 5% - 20%, such as 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14% or 15%, etc., but not limited to the listed numbers, and other unlisted numbers within the above numerical range are equally applicable.

[0025] Preferably, based on the total molar amount of 100%, the molar amount of the cuprous compound is 5% - 20%, such as 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14% or 15%, etc., but not limited to the listed numbers, and other unlisted numbers within the above numerical range are equally applicable.

[0026] Preferably, the method of mixing includes grinding and / or ball milling.

[0027] As a preferred technical solution of the present invention, the temperature of the first melting is 1000 - 1500 °C, such as 1000 °C, 1050 °C, 1100 °C, 1150 °C, 1200 °C, 1250 °C, 1300 °C, 1350 °C, 1400 °C, 1450 °C or 1500 °C, etc., but not limited to the listed numbers, and other unlisted numbers within the above numerical range are equally applicable.

[0028] Preferably, the time for the first melting is 10 to 25 minutes, such as 10 minutes, 11 minutes, 12 minutes, 13 minutes, 14 minutes, 15 minutes, 16 minutes, 17 minutes, 18 minutes, 19 minutes, 20 minutes, 21 minutes, 22 minutes, 23 minutes, 24 minutes or 25 minutes, etc., but not limited to the listed numbers, and other unlisted numbers within the above numerical range are equally applicable.

[0029] Preferably, the cooling method includes pouring the melted melt onto a clean stainless steel plate and cooling it naturally.

[0030] Preferably, the method for obtaining the clean stainless steel plate includes wiping the stainless steel plate with alcohol and then placing it in a vacuum furnace or inert atmosphere furnace at 300 to 400 °C, such as 300 °C, 310 °C, 320 °C, 330 °C, 340 °C, 350 °C, 360 °C, 370 °C, 380 °C, 390 °C or 400 °C, etc., keeping it warm for 1 to 3 hours and then cooling it with the furnace, such as 1 hour, 1.2 hours, 1.4 hours, 1.6 hours, 1.8 hours, 2 hours, 2.2 hours, 2.4 hours, 2.6 hours, 2.8 hours or 3 hours, etc., but not limited to the listed numbers, and other unlisted numbers within the above numerical range are equally applicable.

[0031] Preferably, the preparation method further includes crushing and grinding after the cooling and before the second melting.

[0032] The preparation method preferably requires crushing and grinding the cooled sample before the second melting, so as to quickly reach the melting state during the second melting, shorten the melting time, and at the same time, the prior crushing and grinding also helps to further promote the uniform distribution between silicon and copper during the second melting, and the full volatilization and removal of other impurity elements, especially halogen elements.

[0033] Preferably, the particle size of the sample after crushing and grinding is less than or equal to 100 mesh.

[0034] As a preferred technical solution of the present invention, the temperature of the second melting is 1000 °C to 1500 °C, such as 1000 °C, 1050 °C, 1100 °C, 1150 °C, 1200 °C, 1250 °C, 1300 °C, 1350 °C, 1400 °C, 1450 °C or 1500 °C, etc., but not limited to the listed numbers, and other unlisted numbers within the above numerical range are equally applicable.

[0035] Preferably, the temperature of the first melting is higher than the temperature of the second melting.

[0036] Preferably, the time of the second melting is 15 to 45 minutes, such as 15 minutes, 17 minutes, 19 minutes, 21 minutes, 23 minutes, 25 minutes, 27 minutes, 29 minutes, 31 minutes, 33 minutes, 35 minutes, 37 minutes, 39 minutes, 41 minutes, 43 minutes or 45 minutes, etc., but not limited to the listed numbers, and other unlisted numbers within the above numerical range are equally applicable.

[0037] The function of the first melting is pre-melting. The purpose is to allow copper elements to melt into silicon and at the same time volatilize halogen elements, but this step will increase internal stress; while the purpose of the second melting is to eliminate internal stress to prepare for subsequent nucleation and crystallization of nano-copper, and at the same time it also plays a role in further dispersing copper elements evenly and fully eliminating halogen elements. Therefore, the lack of the second melting will cause the problem that nano-copper cannot nucleate due to the large internal stress during pre-melting. To achieve the above purposes, preferably, the temperature of the first melting is higher than that of the second melting, and the time of the first melting is less than that of the second melting.

[0038] Preferably, both the first melting and the second melting are carried out in a crucible.

[0039] Preferably, the crucible includes any one of a platinum crucible, an alumina crucible or a silicon carbide crucible.

[0040] Preferably, both the first melting and the second melting are carried out in a vacuum furnace or an inert atmosphere furnace.

[0041] Preferably, the inert atmosphere includes any one or a combination of at least two of nitrogen, helium or argon. Typical but non-limiting examples of the combination include a combination of nitrogen and helium, a combination of nitrogen and argon, or a combination of argon and helium.

[0042] As a preferred technical solution of the present invention, after the second melting and before the heat preservation growth, the molten liquid is transferred to a graphite mold.

[0043] Preferably, the shape of the graphite mold includes square or circular.

[0044] Preferably, before use, the graphite mold is first wiped with alcohol and then placed in a vacuum furnace or an inert atmosphere furnace at 300 to 400 °C, such as 300 °C, 310 °C, 320 °C, 330 °C, 340 °C, 350 °C, 360 °C, 370 °C, 380 °C, 390 °C or 400 °C, etc., and after heat preservation for 1 to 3 hours, it is cooled with the furnace, such as 1 hour, 1.2 hours, 1.4 hours, 1.6 hours, 1.8 hours, 2 hours, 2.2 hours, 2.4 hours, 2.6 hours, 2.8 hours or 3 hours, etc., but not limited to the listed numbers, and other unlisted numbers within the above numerical range are equally applicable.

[0045] Performing the above treatment on the mold can achieve its cleaning on the one hand and annealing during heat preservation on the other hand, effectively removing stress.

[0046] As a preferred technical solution of the present invention, the heat preservation temperature is 500 - 600 °C, such as 500 °C, 510 °C, 520 °C, 530 °C, 540 °C, 550 °C, 560 °C, 570 °C, 580 °C, 590 °C or 600 °C, etc., but not limited to the listed numbers, and other unlisted numbers within the above numerical range are equally applicable.

[0047] Preferably, the time for heat preservation growth is 1 - 3 h, such as 1 h, 1.2 h, 1.4 h, 1.6 h, 1.8 h, 2 h, 2.2 h, 2.4 h, 2.6 h, 2.8 h or 3 h, etc., but not limited to the listed numbers, and other unlisted numbers within the above numerical range are equally applicable.

[0048] During the heat preservation growth stage, the nucleation of nanocopper requires energy. Therefore, too low a heat preservation temperature will result in no nucleation, and too high a temperature will cause the copper atoms to move too fast to form copper nanoclusters, and the particle size of the copper nanoparticles cannot meet the requirements; considering that nucleation and growth require time, an appropriate heat preservation time should also be coordinated, so that it is not too short to nucleate and grow, or too long to cause the growth of nanocopper to be too large, affecting subsequent performance.

[0049] As a preferred technical solution of the present invention, it includes the following steps:

[0050] (1) Grind the silicon wafer and / or silicon powder and sieve through a 100 - 500 mesh sieve to obtain silicon raw materials. Based on the total molar amount of 100%, take 60% - 90% of the silicon raw materials, 5% - 20% of the reducing agent, and 5% - 20% of the cuprous compound for grinding to make the components mix evenly. The reducing agent includes SiC and / or Si3N4, and the cuprous compound includes any one or a combination of at least two of CuI, CuCl, or CuBr. Transfer the mixed sample into a platinum crucible, place it in a vacuum furnace or an inert atmosphere furnace, and then perform the first melting at 1000 - 1500 °C for 10 - 25 min;

[0051] (2) Prepare a stainless steel plate, wipe it with alcohol, place it in a vacuum furnace or an inert atmosphere furnace at 300 - 400 °C for heat preservation for 1 - 3 h and then cool it with the furnace. Pour the melted melt obtained in step (1) onto the clean stainless steel plate and let it cool naturally, then break it and grind it, sieve through 100 mesh, transfer the sample into a platinum crucible, place it in a vacuum furnace or an inert atmosphere furnace, and then perform the second melting at 1000 - 1500 °C for 15 - 45 min, and the temperature of the second melting is lower than that of the first melting;

[0052] (3) Prepare a square or circular graphite mold. After wiping it with alcohol, place it in a vacuum furnace or an inert atmosphere furnace at 300 - 400 °C for heat preservation for 1 - 3 h, and then cool it with the furnace. Pour the molten liquid obtained in step (2) into the graphite mold, raise the temperature to 500 - 600 °C for heat preservation and growth for 1 - 3 h to obtain the silicon - copper negative electrode material.

[0053] In a second aspect, the present invention provides a silicon - copper negative electrode material, which is obtained by the preparation method described in the first aspect.

[0054] In a third aspect, the present invention provides a silicon - copper integrated negative electrode, which only contains the silicon - copper negative electrode material described in the second aspect.

[0055] In a fourth aspect, the present invention provides a lithium - ion battery, which includes the silicon - copper integrated negative electrode described in the third aspect and does not contain a negative electrode current collector.

[0056] Generally, the lithium - ion battery at least includes a positive electrode, a separator, and a negative electrode. The present invention does not limit the positive electrode active material in the lithium - ion battery. According to actual working conditions and requirements, lithium iron phosphate, lithium cobalt manganate, lithium manganese iron, lithium cobaltate, lithium nickelate, etc. can be selected. After mixing the positive electrode active material with a conductive agent, etc., it is coated on a positive electrode current collector such as aluminum foil to form a positive electrode; the present invention does not limit the material and thickness of the separator in the lithium - ion battery. For example, a separator with a thickness of 5 - 16 μm can be selected to isolate the positive electrode plate from the silicon - copper integrated negative electrode, and the positive electrode - separator - negative electrode are stacked and placed in an aluminum shell, and an electrolyte is injected; the present invention does not limit the selection of the electrolyte. For example, an electrolyte composed of lithium hexafluorophosphate, dimethyl carbonate, and ethylene carbonate can be selected, and the electrolyte injection coefficient can be 2.5 - 4.5.

[0057] In a fourth aspect, the present invention provides an electrical device, which contains the lithium - ion battery described in the third aspect.

[0058] Compared with the prior art solutions, the present invention has at least the following beneficial effects:

[0059] The present invention can obtain the silicon - copper negative electrode material only through a simple high - temperature solid - phase melting method. This material can be formed into a negative electrode during the preparation process and directly serve as the negative electrode of the lithium battery. It does not require additional use of a negative electrode current collector and does not require traditional negative electrode processes such as pulping and coating, greatly simplifying the manufacturing process of the negative electrode and effectively reducing costs, improving the energy density of the battery. It can save costs under the same CB value. Cu doping makes the obtained material have excellent electrical conductivity, with a low electrode sheet resistance, which is more conducive to charge exchange. And because there is no need for slurry coating and cold pressing processes, during the cycling process, the situation of negative electrode sheet powder falling is avoided, effectively improving the cycling stability. Description of the Drawings

[0060] Figure 1 is a picture of the silicon-copper negative electrode material obtained in Example 1;

[0061] Figure 2 This is a luminescent image of the silicon-copper negative electrode material obtained in Example 1 under light of 300nm wavelength;

[0062] Figure 3 is a transmission electron microscope image of the silicon-copper negative electrode material obtained in Example 1;

[0063] Figure 4 It is the EIS test graph of the silicon-copper negative electrode material obtained in Example 1 and Comparative Examples 1-5. DETAILED DESCRIPTION

[0064] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and through specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0065] Example 1

[0066] This embodiment provides a method for preparing a silicon-copper negative electrode material, the preparation method comprising the following steps:

[0067] (1) Grind silicon powder and pass it through a 100-mesh sieve as a silicon raw material. Based on the total molar amount of 100%, take 70% of the silicon raw material, 15% of the reducing agent Si3N4 and 15% of the cuprous compound CuI and grind them thoroughly in an agate mortar to mix the components evenly. Transfer the mixed sample into a platinum crucible, place it in a vacuum furnace, and then perform a first melting at 1200°C for 10 minutes;

[0068] (2) Prepare a stainless steel plate, wipe it with alcohol, place it in a vacuum muffle furnace at 350° C. for 2 h, and then cool it in the furnace. Pour the molten molten metal obtained in step (1) onto a clean stainless steel plate and cool it naturally. Then, crush and grind it, sieve it through 100 mesh, transfer the sample into a platinum crucible, place it in a vacuum furnace, and then perform a second melting at 1100° C. for 15 min.

[0069] (3) Prepare a square graphite mold, wipe it with alcohol, place it in a vacuum furnace or an inert atmosphere furnace at 350°C for 2 hours, and then cool it with the furnace. Pour the molten melt obtained in step (2) into the graphite mold, increase the temperature to 550°C and keep it warm for 3 hours to obtain a silicon-copper negative electrode material.

[0070] Figure 1 This is a picture of the silicon-copper negative electrode material obtained in Example 1. Figure 2The luminescence picture of the silicon-copper anode material obtained in Example 1 under 300-nm wavelength light. Since nano-copper can emit white light under 300-nm wavelength light, therefore, Figure 2 It is proved that the nano-Cu in the silicon-copper anode material obtained in Example 1 is very evenly dispersed.

[0071] Figure 3 The transmission electron microscope image of the silicon-copper anode material obtained in Example 1. The figure shows the nano-copper particles generated in the silicon-copper anode material, and the particle size of the nano-copper particles is 20 nm.

[0072] Example 2

[0073] This example provides a preparation method of a silicon-copper anode material. The preparation method includes the following steps:

[0074] (1) Grind silicon powder and silicon wafers and sieve through a 500-mesh sieve to obtain silicon raw materials. Based on the total molar amount being 100%, take 90% of the silicon raw materials, 5% of the reducing agents Si3N4 and SiC, and 5% of the cuprous compound CuCl, and grind them thoroughly in an agate mortar to mix the components evenly. Transfer the mixed sample into an alumina crucible, place it in a vacuum furnace, and then perform the first melting at 1500 °C for 15 min;

[0075] (2) Prepare a stainless-steel plate, wipe it with alcohol, place it in a vacuum muffle furnace at 400 °C for heat preservation for 1 h and then cool it with the furnace. Pour the melted solution obtained in step (1) onto the clean stainless-steel plate and let it cool naturally, then break it up and grind it, sieve through a 100-mesh sieve, transfer the sample into a platinum crucible, place it in a vacuum furnace, and then perform the second melting at 1300 °C for 25 min;

[0076] (3) Prepare a square graphite mold, wipe it with alcohol, place it in a vacuum furnace or an inert atmosphere furnace at 400 °C for heat preservation for 1 h and then cool it with the furnace. Pour the melted solution obtained in step (2) into the graphite mold, raise the temperature to 600 °C for heat preservation and growth for 1 h to obtain the silicon-copper anode material.

[0077] Example 3

[0078] This example provides a preparation method of a silicon-copper anode material. The preparation method includes the following steps:

[0079] (1) Grind silicon wafers and sieve through a 300-mesh sieve to obtain silicon raw materials. Based on the total molar amount being 100%, take 60% of the silicon raw materials, 20% of the reducing agent SiC, and 20% of the cuprous compound CuBr, and grind them thoroughly in an agate mortar to mix the components evenly. Transfer the mixed sample into an alumina crucible, place it in a vacuum furnace, and then perform the first melting at 1000 °C for 25 min;

[0080] (2) preparing a stainless steel plate, wiping it with alcohol, placing it in a vacuum muffle furnace at 300° C. for 3 h and then cooling it in the furnace, pouring the melt obtained in step (1) onto a clean stainless steel plate and cooling it naturally, then crushing and grinding it, sieving it through 100 mesh, transferring the sample into a platinum crucible, placing it in a vacuum furnace, and then performing a second melting at 1000° C. for 45 min;

[0081] (3) Prepare a square graphite mold, wipe it with alcohol, place it in a vacuum furnace or an inert atmosphere furnace at 300°C for 3 hours, and then cool it with the furnace. Pour the molten melt obtained in step (2) into the graphite mold, increase the temperature to 500°C, and keep it warm for 2 hours to obtain a silicon-copper negative electrode material.

[0082] Example 4

[0083] This embodiment provides a method for preparing a silicon-copper negative electrode material. The preparation method is exactly the same as that of Example 1, except that in step (1), 50% of silicon raw material, 25% of reducing agent Si3N4 and 25% of cuprous compound CuI are fully ground in an agate mortar.

[0084] Example 5

[0085] This embodiment provides a method for preparing a silicon-copper negative electrode material. The preparation method is exactly the same as that of Example 1, except that in step (1), 60% of silicon raw material, 20% of reducing agent Si3N4 and 20% of cuprous compound CuI are fully ground in an agate mortar.

[0086] Example 6

[0087] This embodiment provides a method for preparing a silicon-copper negative electrode material. The preparation method is exactly the same as that of Example 1, except that in step (1), 90% of the silicon raw material, 5% of the reducing agent Si3N4 and 5% of the cuprous compound CuI are fully ground in an agate mortar.

[0088] Example 7

[0089] This embodiment provides a method for preparing a silicon-copper negative electrode material. The preparation method is exactly the same as that of Example 1, except that in step (1), 96% of silicon raw material, 2% of reducing agent Si3N4 and 2% of cuprous compound CuI are fully ground in an agate mortar.

[0090] Example 8

[0091] This embodiment provides a method for preparing a silicon-copper negative electrode material. The preparation method is identical to that of Embodiment 1 except that the reducing agent is changed from Si3N4 to SiC in step (1).

[0092] Example 9

[0093] This example provides a method for preparing a silicon - copper negative electrode material. Except that in step (1), the cuprous compound is adjusted from CuI to CuCl, other conditions are exactly the same as those in Example 1.

[0094] Example 10

[0095] This example provides a method for preparing a silicon - copper negative electrode material. Except that in step (1), the cuprous compound is adjusted from CuI to CuBr, other conditions are exactly the same as those in Example 1.

[0096] Example 11

[0097] This example provides a method for preparing a silicon - copper negative electrode material. Except that in step (1), the temperature of the first melting is adjusted from 1200 °C to 950 °C, other conditions are exactly the same as those in Example 1.

[0098] Example 12

[0099] This example provides a method for preparing a silicon - copper negative electrode material. Except that in step (1), the temperature of the first melting is adjusted from 1200 °C to 1550 °C, other conditions are exactly the same as those in Example 1.

[0100] Example 13

[0101] This example provides a method for preparing a silicon - copper negative electrode material. Except that in step (2), the temperature of the second melting is adjusted from 1200 °C to 950 °C, other conditions are exactly the same as those in Example 1.

[0102] Example 14

[0103] This example provides a method for preparing a silicon - copper negative electrode material. Except that in step (2), the temperature of the second melting is adjusted from 1200 °C to 1550 °C, other conditions are exactly the same as those in Example 1.

[0104] Example 15

[0105] This example provides a method for preparing a silicon - copper negative electrode material. Except that in step (2), the time of the second melting is adjusted from 15 min to 10 min, other conditions are exactly the same as those in Example 1.

[0106] Example 16

[0107] This embodiment provides a method for preparing a silicon-copper negative electrode material. Except that in step (2), the second melting time is adjusted from 15 min to 55 min, other conditions are exactly the same as those in Embodiment 1.

[0108] Embodiment 17

[0109] This embodiment provides a method for preparing a silicon-copper negative electrode material. Except that in step (3), the temperature for heat preservation and growth is adjusted from 550 °C to 450 °C, other conditions are exactly the same as those in Embodiment 1.

[0110] Embodiment 18

[0111] This embodiment provides a method for preparing a silicon-copper negative electrode material. Except that in step (3), the temperature for heat preservation and growth is adjusted from 550 °C to 650 °C, other conditions are exactly the same as those in Embodiment 1.

[0112] Comparative Example 1

[0113] In this comparative example, graphite is used as the negative electrode active material. After the negative electrode active material is made into a negative electrode paste, it is coated on a copper foil to serve as the battery negative electrode.

[0114] Comparative Example 2:

[0115] In this comparative example, silicon powder after grinding and passing through a 100-mesh sieve is used as the negative electrode active material. After the negative electrode active material is made into a negative electrode paste, it is coated on a copper foil to serve as the battery negative electrode.

[0116] Comparative Example 3:

[0117] In this comparative example, a silicon wafer with a suitable size is used as the battery negative electrode.

[0118] Comparative Example 4

[0119] This comparative example provides a method for preparing a silicon-copper negative electrode material. In this method, the second melting is not carried out, that is, step (2) is not performed. Instead, the molten liquid obtained in step (1) is directly poured into a graphite mold in step (3) for heat preservation and growth. Except for the above, other conditions are exactly the same as those in Embodiment 1.

[0120] Comparative Example 5

[0121] This comparative example provides a method for preparing a silicon-copper negative electrode material. In this method, heat preservation and growth are not carried out. That is, in step (3), the molten liquid obtained in step (2) is poured into a graphite mold, and the sample after natural cooling is used as the silicon-copper negative electrode material. Except for the above, other conditions are exactly the same as those in Embodiment 1.

[0122] Comparative Example 6

[0123] This comparative example provides a method for preparing a silicon-copper negative electrode material. Except that in step (2), instead of being crushed and ground, it directly undergoes a second melting, other conditions are exactly the same as those in Example 1.

[0124] Since the silicon-copper negative electrode materials obtained in Examples 1-18 and Comparative Examples 4-6 have been formed in a graphite mold, they can be directly used as the negative electrode. The obtained negative electrodes and the negative electrodes obtained in Comparative Examples 1-3 are respectively assembled into coin cells: After making a positive electrode slurry from lithium iron phosphate and a conductive agent and coating it on a 6-μm aluminum foil to form a positive electrode, a 12-μm separator is selected, and they are stacked in the order of positive electrode-separator-negative electrode and placed into an aluminum shell. An electrolyte composed of lithium hexafluorophosphate, ethylene carbonate, and dimethyl carbonate is injected, and the injection coefficient is 3 to obtain coin cells, and the following tests are carried out:

[0125] (1) Polar resistance: After the negative electrodes made in each scheme are completed, EIS tests are carried out, and the polar film resistance values are calculated; among them, the EIS test results of Example 1 and Comparative Examples 1-5 are recorded in Table 1;

[0126] (2) Energy density (0.5C / 2.5V): Under the conditions of setting the same battery capacity and the same CB value, the mass energy density of the batteries in each scheme is measured; the CB value (cell Balance) is the margin by which the negative electrode capacity exceeds the positive electrode capacity on the opposite side within the same stage and under the same conditions, or is also called N / P (Negative / Positive). CB value calculation formula: CB value = (gram capacity of negative electrode active material × negative electrode surface density × content ratio of negative electrode active material) ÷ (gram capacity of positive electrode active material × positive electrode surface density × content ratio of positive electrode active material).

[0127] (3) Cycle test: The batteries made in each scheme are subjected to 1C / 1C conventional cycling for 1000 cycles, and the remaining capacity is measured;

[0128] The above data results are recorded in Table 2.

[0129] Table 1

[0130] Item SEI film impedance Rsei (Ω) Interface impedance Rct (Ω) Ion diffusion impedance w (Ω) Example 1 18.2 34.1 59.1 Comparative Example 1 26.4 61.5 64.5 Comparative Example 2 22.3 46.2 60.3 Comparative Example 3 19.8 40.7 61.2 Comparative Example 4 21.1 42.4 62.7 Comparative Example 5 31.5 70.9 69.6

[0131] Figure 4 For the EIS test diagrams of the silicon-copper negative electrode materials obtained in Example 1 and Comparative Examples 1-5, from Figure 4It can be seen from Table 1 that in Example 1, with the above-mentioned scheme, the film-forming property is better, resulting in a lower impedance of the SEI film. After doping with nano-copper, the sheet resistance of the film is reduced, which is beneficial to charge exchange and transfer, so the interfacial impedance is lower. In Comparative Example 1 and Comparative Example 2, due to the coating process, the pores of the electrode sheet are large, the ion transport path is long, the resistance increases, and at the same time, the interface is rough, resulting in uneven film-forming thickness and an increase in SEI impedance. In Comparative Example 3, due to the absence of doping with nano-copper, and in Comparative Example 4, due to the failure to perform the second melting, the nano-copper fails to precipitate successfully, resulting in an increase in the sheet resistance of the electrode sheet. In Comparative Example 5, due to the failure to perform heat preservation growth, the obtained product is a silicon-copper mixture, resulting in a decrease in the performance of the electrode sheet instead.

[0132] Table 2

[0133]

[0134]

[0135] It can be seen from Table 2 that:

[0136] In Example 1, due to the use of a silicon negative electrode material, its energy density has been significantly improved. At the same time, uniformly doped nano-copper particles have significantly reduced the sheet resistance of the electrode sheet. This process has no problems such as powder falling off the electrode sheet, and has good cycle stability.

[0137] In Examples 4-7, when the proportion of copper increases, it will lead to a decrease in energy density. Even in the extreme case where the cuprous compound is severely insufficient and the nano-copper cannot precipitate, the sheet resistance will be greatly increased and the performance of the electrode sheet will be reduced.

[0138] In Example 8, the reducing agent is changed to SiC. Since the melting temperature of SiC is higher and the reducibility of SiC is lower than that of Si3N4, when other manufacturing processes are the same, the performance of the silicon nano-copper material prepared is reduced. In Examples 9 and 10, CuCl and CuBr are used instead of CuI. Since CuI is stable in air at room temperature while CuCl and CuBr are not stable, they are easily oxidized during the early mixing process, thus affecting the performance of the subsequent materials.

[0139] It can be seen from Examples 11 to 18 that when the temperature and time of the first melting, the second melting, or the heat preservation growth are not appropriate, the crystallization of nano-copper and the removal of halogen elements cannot reach the best state, so the performance of the subsequent materials is affected. Therefore, compared with Example 1, the performance of the electrode sheet has decreased to varying degrees.

[0140] The present invention illustrates the detailed structural features of the present invention through the above embodiments. However, the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvement to the present invention, the equivalent replacement of the components selected for the present invention, the addition of auxiliary components, and the selection of specific methods, etc., all fall within the protection scope and the disclosure scope of the present invention.

[0141] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0142] In addition, it should be noted that, among the various specific technical features described in the above specific embodiments, they can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not separately describe various possible combination methods.

[0143] Furthermore, any combination can be made between various different embodiments of the present invention, as long as it does not violate the idea of the present invention, it should also be regarded as the content disclosed by the present invention.

Claims

1. A preparation method of a silicon-copper negative electrode material, characterized in that, It includes the following steps: Mix the silicon raw material, reducing agent and cuprous compound evenly, conduct the first melting, cool it and then conduct the second melting, and then reduce the temperature to the heat preservation temperature for heat preservation growth to obtain the silicon-copper anode material; The temperature of the first melting is 1000~1500°C, and the time of the first melting is 10~25 min; The temperature of the second melting is 1000°C~1500°C, and the time of the second melting is 15~45 min; Calculated by the total molar amount of 100%, the molar amount of the silicon raw material is 60%~90%, the molar amount of the reducing agent is 5%~20%, and the molar amount of the cuprous compound is 5%~20%; The reducing agent includes SiC and / or Si3N4; The cuprous compound includes any one or a combination of at least two of CuI, CuCl or CuBr.

2. The preparation method according to claim 1, characterized in that, The silicon raw material includes silicon wafers and / or silicon powder.

3. The preparation method according to claim 2, characterized in that, The silicon raw material is silicon powder.

4. The preparation method according to claim 1, characterized in that, The silicon raw material is ground and sieved before mixing, and the particle size reaches 100~500 mesh.

5. The preparation method according to claim 1, characterized in that, The reducing agent is Si3N4.

6. The preparation method according to claim 1, characterized in that, The cuprous compound is CuI.

7. The preparation method according to claim 1, characterized in that, The mixing method includes grinding and / or ball milling.

8. The preparation method according to claim 1, characterized in that, The cooling method includes pouring the melted melt on a clean stainless steel plate for natural cooling.

9. The preparation method according to claim 8, characterized in that, The method for obtaining the clean stainless steel plate includes wiping the stainless steel plate with alcohol, placing it in a vacuum furnace or inert atmosphere furnace at 300~400°C for heat preservation for 1~3 h and then cooling with the furnace.

10. The preparation method according to claim 1, characterized in that, The preparation method further includes conducting crushing and grinding after the cooling and before the second melting.

11. The preparation method according to claim 10, characterized in that, The particle size of the sample after crushing and grinding is less than or equal to 100 mesh.

12. The preparation method according to claim 1, characterized in that, The temperature of the first melting is higher than the temperature of the second melting.

13. The preparation method according to claim 1, wherein Both the first melting and the second melting are carried out in a crucible.

14. The preparation method according to claim 13, characterized in that, The crucible includes any one of a platinum crucible, an alumina crucible or a silicon carbide crucible.

15. The preparation method according to claim 1, characterized in that, Both the first melting and the second melting are carried out in a vacuum furnace or an inert atmosphere furnace.

16. The preparation method according to claim 15, characterized in that, The inert atmosphere includes any one or a combination of at least two of nitrogen, helium or argon.

17. The preparation method according to claim 1, characterized in that, After the second melting and before the heat preservation growth, transfer the melted melt to a graphite mold.

18. The preparation method according to claim 17, wherein The shape of the graphite mold includes square or circular.

19. The preparation method according to claim 17, characterized in that, The graphite mold is wiped with alcohol before use, placed in a vacuum furnace or inert atmosphere furnace at 300~400°C for heat preservation for 1~3 h and then cooled with the furnace.

20. The preparation method according to claim 1, characterized in that, The heat preservation temperature is 500~600°C.

21. The preparation method according to claim 1, characterized in that, The time of heat preservation growth is 1~3 h.

22. The preparation method according to claim 1, characterized in that, It includes the following steps: (1) Grind the silicon wafers and / or silicon powder and sieve them through a 100~500 mesh sieve as the silicon raw material. Calculated by the total molar amount of 100%, take 60%~90% of the silicon raw material, 5%~20% of the reducing agent and 5%~20% of the cuprous compound for grinding to make each component mix evenly. The reducing agent includes SiC and / or Si3N4, and the cuprous compound includes any one or a combination of at least two of CuI, CuCl or CuBr. Transfer the mixed sample into a platinum crucible, place it in a vacuum furnace or an inert atmosphere furnace, and then conduct the first melting at 1000~1500°C for 10~25 min; (2)Prepare a stainless-steel plate. After wiping it with alcohol, place it in a vacuum furnace or an inert atmosphere furnace at 300 - 400 °C and keep it warm for 1 - 3 h, then cool it with the furnace. Pour the melted liquid obtained in step (1) onto the clean stainless-steel plate and let it cool naturally. Then break it up, grind it, and sieve it through a 100-mesh sieve. Transfer the sample into a platinum crucible, place it in a vacuum furnace or an inert atmosphere furnace, and then conduct a second melting at 1000 - 1500 °C for 15 - 45 min, and the temperature of the second melting is lower than the temperature of the first melting; (3)Prepare a square or circular graphite mold. After wiping it with alcohol, place it in a vacuum furnace or an inert atmosphere furnace at 300 - 400 °C and keep it warm for 1 - 3 h, then cool it with the furnace. Pour the melted liquid obtained in step (2) into the graphite mold, raise the temperature to 500 - 600 °C, and keep it warm for growth for 1 - 3 h to obtain the silicon-copper negative electrode material.

23. A silicon-copper anode material, characterized in that, Obtained by the preparation method according to any one of claims 1 - 22.

24. A silicon-copper integrated negative electrode, characterized in that, The silicon-copper integrated negative electrode only contains the silicon-copper negative electrode material according to claim 23.

25. A lithium-ion battery, characterized in that, The lithium-ion battery includes the silicon-copper integrated negative electrode according to claim 24 and does not contain a negative electrode current collector.

26. An electrical device, characterized in that, The electrical device contains the lithium-ion battery according to claim 25.

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