Silicon-carbon negative electrode material, and preparation method therefor and use thereof

Abstract

The present application relates to the technical field of batteries, and specifically relates to a silicon-carbon negative electrode material, and a preparation method therefor and the use thereof. The silicon-carbon negative electrode material of the present application comprises a base body and a coating layer coating the surface of the base body, wherein the base body comprises an inner core and a composite layer located on the surface of the inner core, with the inner core comprising graphite, and the composite layer comprising nano silicon and boron oxide; and the coating layer comprises nano carbon. In the silicon-carbon negative electrode material of the present application, graphite serves as the inner core, and by means of boron oxide, nano silicon is uniformly adhered to the surface of graphite, such that the adhesion of nano silicon to graphite can be improved, thereby preventing the silicon material from falling off the surface of graphite during a charging and discharging process. The nano carbon coating layer can avoid side reactions caused by direct contact of silicon particles with an electrolyte, and can also increase the electronic conductivity of the silicon-carbon negative electrode material. The silicon-carbon negative electrode material of the present application has excellent comprehensive electrochemical performance.

Description

Silicon-carbon negative electrode material and preparation method and application thereof

[0001] Cross-reference to related applications

[0002] The present application claims priority to the Chinese patent application No.CN202411089086X, filed on August 09, 2024, and entitled "Silicon-carbon negative electrode material and preparation method and application thereof", the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0003] The present application relates to the technical field of batteries, in particular to a silicon-carbon negative electrode material and a preparation method and application thereof. BACKGROUND

[0004] The theoretical specific capacity of graphite, a negative electrode of lithium ion battery, is only 372mAh / g, which cannot meet the demand of high specific energy lithium ion battery. Silicon has a high theoretical specific capacity of 4200mAh / g and is considered to be the most promising material to replace graphite negative electrode. However, silicon has a volume change of up to 300% during charging and discharging, which causes repeated expansion and contraction during charging and discharging, resulting in large internal stress in the material, leading to the breakage of silicon particles and the serious pulverization of the electrode. In addition, the electronic and ionic conductivities of silicon negative electrode are low, which seriously restricts its wide commercial application. By dispersing silicon active particles in a conductive carbon matrix to form a silicon-carbon composite material, the high specific capacity of silicon and the high conductivity of carbon are taken into account, and the carbon material is also beneficial to buffering the volume expansion of silicon particles, so the silicon-carbon composite material is expected to become one of the next generation of lithium ion battery negative electrode materials for commercial application.

[0005] At present, there are many studies on the structural design of silicon-carbon composite materials, such as core-shell structure, yolk structure, porous structure and embedded structure, etc. These structural designs cannot solve the problems of poor interfacial adhesion between silicon and carbon matrix, easy loss of electrical contact during continuous charging and discharging, limited effect of relieving the volume change of silicon and improving the conductivity of the material.

[0006] Therefore, the present application is proposed.

[0007] SUMMARY

[0008] Therefore, in a first aspect, the present application aims to provide a silicon-carbon negative electrode material to solve the problem of poor conductivity of the negative electrode material caused by the weak adhesion between the silicon material and the carbon material in the prior art, which makes the silicon particles easy to separate from the surface of the carbon material.

[0009] The silicon-carbon anode material provided in this application includes a matrix and a coating layer covering the surface of the matrix. The matrix includes a core and a composite layer located on the surface of the core. The core contains graphite. The composite layer contains nano-silicon and boron oxide. The coating layer contains nano-carbon.

[0010] Beneficial effects: This silicon-carbon anode material uses graphite as its core, and the co-solvent boron oxide uniformly adheres the nano-silicon to the graphite surface, which can improve the adhesion between the nano-silicon and the graphite and prevent the silicon material from falling off the graphite surface during charging and discharging. The nano-carbon coating layer can prevent the silicon particles from directly contacting the electrolyte and causing side reactions, while also increasing the electronic conductivity of the silicon-carbon anode material. The silicon-carbon anode material of this application has excellent comprehensive electrochemical performance.

[0011] In one alternative embodiment, the graphite comprises spherical graphite.

[0012] In one optional embodiment, the battery prepared from the silicon-carbon anode material has an initial discharge specific capacity of over 440 mAh / g under test conditions of 25°C, 0.1C, and 0.05–2.5V.

[0013] In one alternative embodiment, the initial coulombic efficiency of the battery prepared from the silicon-carbon anode material is 79% or higher.

[0014] Secondly, this application provides a method for preparing the aforementioned silicon-carbon anode material, comprising the following steps:

[0015] Graphite, nano-silicon, boron compound and water are first mixed and first calcined to obtain a matrix material; the matrix material is then second mixed and second calcined with a pyrolytic carbon source solution to obtain a silicon-carbon anode material.

[0016] Beneficial effects: This preparation method is simple and easy to implement. By first mixing and calcining graphite, nano-silicon, boron compound, and water, the liquefaction and ductility of boron compound during low-temperature calcination are utilized to achieve uniform dispersion and firm adhesion of nano-silicon on the graphite surface, effectively suppressing the separation and agglomeration of silicon from the graphite matrix during charging and discharging. Further, the matrix material is mixed and calcined with a pyrolytic carbon source solution in a second process to form a uniform nano-carbon coating layer on the surface of the matrix material. This avoids direct contact between silicon particles and electrolyte, preventing side reactions, while buffering the volume expansion of silicon particles and increasing the electronic conductivity of the silicon-carbon anode material.

[0017] In one alternative embodiment, the boron compound comprises at least one of boron oxide and boric acid.

[0018] In an alternative embodiment, the pyrolytic carbon source solution comprises the pyrolytic carbon source and water, and the pyrolytic carbon source accounts for 5% to 8% of the mass content of the pyrolytic carbon source solution; the pyrolytic carbon source comprises water-soluble carbon source and / or water-insoluble carbon source.

[0019] In an alternative embodiment, the mass ratio of the nano-silicon and the graphite is x:(1-x), wherein 0 < x ≤ 0.4.

[0020] In an alternative embodiment, the mass ratio of the boron element in the boron compound to the total mass of the nano-silicon and the graphite is y:1, wherein 0 < y ≤ 0.1.

[0021] In an alternative embodiment, the mass ratio of the boron compound and the water is 1:(30-40).

[0022] In an alternative embodiment, the mass ratio of the pyrolytic carbon source in the pyrolytic carbon source solution to the base material is (2-6):(1-5).

[0023] In an alternative embodiment, the rotation speed of the first mixing is 1500-2000 rpm, and the time of the first mixing is 20-40 min.

[0024] In an alternative embodiment, the temperature of the first roasting is 300-600℃, and the time of the first roasting is 1-10 h.

[0025] In an alternative embodiment, the first roasting is performed under a protective gas condition.

[0026] In an alternative embodiment, the first mixing and the first roasting further comprise a first drying.

[0027] In an alternative embodiment, the temperature of the first drying is 80-120℃, and the time of the first drying is 24-48 h.

[0028] In an alternative embodiment, the first roasting further comprises: sequentially performing a first crushing treatment and a first screening treatment on the material after the first roasting.

[0029] In an alternative embodiment, the rotation speed of the first crushing treatment is 200-300 rpm, and the time of the first crushing treatment is 4-5 h.

[0030] In an alternative embodiment, the first screening treatment comprises: passing through a 350-mesh sieve.

[0031] In an alternative embodiment, the rotation speed of the second mixing is 1500-2000 rpm, and the time of the second mixing is 20-40 min.

[0032] In an alternative embodiment, the second calcination is performed at a temperature of 600-950℃ for 1-10h.

[0033] In an alternative embodiment, the second calcination is performed under a protective gas.

[0034] In an alternative embodiment, the second mixing and the second calcination are further followed by a second drying.

[0035] In an alternative embodiment, the second drying is performed at a temperature of 80-120℃ for 24-48h.

[0036] In an alternative embodiment, the second calcination is further followed by a second crushing and a second screening.

[0037] In an alternative embodiment, the second crushing is performed at a rotation speed of 200-300rpm for 4-5h.

[0038] In an alternative embodiment, the second screening comprises passing through a 350-mesh sieve.

[0039] In a third aspect, the present application provides a negative electrode sheet comprising the silicon-carbon negative electrode material or the silicon-carbon negative electrode material prepared by the preparation method.

[0040] In a fourth aspect, the present application provides a battery comprising the negative electrode sheet.

[0041] Beneficial effects: the obtained battery has high initial efficiency, good cycle performance, rate performance and safety performance.

[0042] In a fifth aspect, the present application provides a power-using device comprising the battery. BRIEF DESCRIPTION OF DRAWINGS

[0043] In order to more clearly illustrate the technical solutions of the present application or prior art, the following will briefly introduce the drawings needed to be used in the description of the specific embodiments or prior art. Obviously, the drawings described below are some embodiments of the present application, and those skilled in the art can obtain other drawings according to these drawings without creative effort.

[0044] Fig. 1 is a structural schematic diagram of the silicon-carbon negative electrode material of the present application.

[0045] Reference signs: 1 - substrate, 101 - inner core, 102 - composite layer, 2 - coating layer. DETAILED DESCRIPTION

[0046] The embodiments of the present application will be described in detail below with examples, but those skilled in the art will understand that the following examples are only for illustration of the present application and should not be regarded as limiting the scope of the present application. The specific conditions are not specified in the examples, and the conventional conditions or the conditions recommended by the manufacturer are used. The reagents or instruments used are not specified by the manufacturer, and are all conventional products that can be obtained by purchase.

[0047] According to one aspect of the present application, the present application relates to a silicon-carbon negative electrode material, comprising a substrate and a coating layer coated on the surface of the substrate, the substrate comprising a core and a composite layer on the surface of the core; the core comprises graphite; the composite layer comprises nano-silicon and boron oxide; and the coating layer comprises nano-carbon.

[0048] The silicon-carbon negative electrode material of the present application uses graphite as the core, and the boron oxide as the cosolvent to uniformly adhere the nano-silicon to the surface of the graphite, which can improve the adhesion of the nano-silicon and the graphite and avoid the silicon material from falling off the surface of the graphite during the charging and discharging process; the nano-carbon coating layer can avoid the side reaction of the silicon particles and the electrolyte from directly contacting, and at the same time, can increase the electronic conductivity of the silicon-carbon negative electrode material. Therefore, the silicon-carbon negative electrode material of the present application has excellent comprehensive electrochemical performance.

[0049] In some embodiments, the graphite comprises spherical graphite.

[0050] In some embodiments, the battery prepared by using the silicon-carbon negative electrode material has a first discharge specific capacity of 440 mAh / g or more, for example, 445 mAh / g, 480 mAh / g, 500 mAh / g, 550 mAh / g, 600 mAh / g, or any range value between any two of them, under the test conditions of 25°C, 0.1C, and 0.05-2.5V.

[0051] In some embodiments, the battery prepared by using the silicon-carbon negative electrode material has a first coulombic efficiency of 79% or more, for example, 79%, 80%, 82%, 85%, 88%, 90%, 91%, or any range value between any two of them.

[0052] According to another aspect of the present application, the present application also relates to a preparation method of the silicon-carbon negative electrode material as described above, comprising the following steps:

[0053] The graphite, nano-silicon, boron compound, and water are subjected to first mixing and first calcination to obtain a substrate material; and the substrate material is subjected to second mixing and second calcination with a pyrolytic carbon source solution to obtain the silicon-carbon negative electrode material.

[0054] The preparation method of the silicon-carbon negative electrode material is simple and easy to implement. The silicon-carbon negative electrode material is prepared by first mixing graphite, nano-silicon, a boron compound, and water, and first roasting. The boron compound is liquefied and has ductility at low temperature, so that the nano-silicon is uniformly dispersed on the surface of the graphite and firmly adheres to the surface of the graphite, effectively inhibiting the separation and agglomeration of the silicon and the graphite matrix during the charging and discharging process. Further, the matrix material is second mixed with a pyrolytic carbon source solution, and second roasting is performed, so that a uniform nano-carbon coating layer is formed on the surface of the matrix material. The nano-carbon coating layer avoids the side reaction of the silicon particles and the electrolyte directly contacting each other, buffers the volume expansion of the silicon particles, and increases the electronic conductivity of the silicon-carbon negative electrode material.

[0055] In some embodiments, the boron compound includes at least one of boron oxide and boric acid.

[0056] In some embodiments, the pyrolytic carbon source solution includes a pyrolytic carbon source and water, and the mass content of the pyrolytic carbon source in the pyrolytic carbon source solution is 5% to 8%, for example, 5%, 5.5%, 6%, 6.5%, 7%, and the like. The pyrolytic carbon source includes a water-soluble carbon source and / or a non-water-soluble carbon source. The water-soluble carbon source includes polyvinylidene fluoride (PVDF). The non-water-soluble carbon source includes starch.

[0057] In some embodiments, the mass ratio of the nano-silicon and the graphite is x:(1-x), where 0

[0058] In some embodiments, the mass ratio of boron in the boron compound to the total mass of the nanosilicon and graphite is y:1, where 0 < y ≤ 0.1. In some embodiments, y includes but is not limited to 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, or 0.1, or any range between any two of these values. In some embodiments, the mass ratio of boron in the boron compound to the total mass of the nanosilicon and graphite includes but is not limited to 0.01:1, 0.02:1, 0.03:1, 0.05:1, 0.06:1, 0.07:1, 0.08:1, 0.09:1, 0.1:1. The present application uses an appropriate amount of boron compound, which can make the obtained boron oxide better adhere the nanosilicon to the surface of the graphite, and can improve the adhesion of the nanosilicon and the graphite.

[0059] In some embodiments, the mass ratio of the boron compound to water is 1:(30-40). The water includes deionized water and the like. In some embodiments, the mass ratio of the boron compound to water includes but is not limited to 1:30, 1:32, 1:33, 1:35, 1:38, 1:40, and the like. The present application uses an appropriate amount of water to ensure that the materials are fully mixed and uniform, which is beneficial for subsequent operations to ensure the performance of the base material.

[0060] In some embodiments, the mass ratio of the pyrolysis carbon source in the pyrolysis carbon source solution to the base material is (2-6):(1-5). The mass ratio of the pyrolysis carbon source to the base material ensures that the coating layer has an appropriate thickness and uniformity to improve the electrochemical performance of the final obtained silicon-carbon negative electrode material.

[0061] In some embodiments, the rotation speed of the first mixing is 1500-2000 rpm, including but not limited to 1500 rpm, 1600 rpm, 1700 rpm, 1800 rpm, 1850 rpm, 1900 rpm, 1950 rpm, 2000 rpm, or any range between any two of these values; and the time of the first mixing is 20-40 min, including but not limited to 20 min, 25 min, 30 min, 35 min, 40 min, or any range between any two of these values. The present application uses an appropriate rotation speed and time of the first mixing to ensure that the materials are fully mixed.

[0062] In some embodiments, the first baking is performed at a temperature of 300-600°C, including but not limited to 300°C, 350°C, 400°C, 500°C, 600°C, or any range between any two of the foregoing temperatures; and a time of 1-10 hours, including but not limited to 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, or any range between any two of the foregoing times. The first baking is performed under a protective gas, such as nitrogen, argon, helium, etc. The suitable first baking conditions of the present application are conducive to ensuring the binding effect of the cosolvent and improving the electrochemical performance of the base material.

[0063] In some embodiments, the first mixing is followed by a first drying. The first drying is performed to remove moisture. The first drying is performed at a temperature of 80-120°C, including but not limited to 80°C, 85°C, 90°C, 95°C, 100°C, 110°C, 120°C, or any range between any two of the foregoing temperatures; and a time of 24-48 hours, including but not limited to 24 hours, 25 hours, 30 hours, 35 hours, 40 hours, 45 hours, 48 hours, or any range between any two of the foregoing times.

[0064] In some embodiments, the first baking is followed by a first crushing and a first sieving. The first crushing and the first sieving are performed to obtain a base material with a suitable particle size. In some embodiments, the first crushing is performed at a speed of 200-300 rpm, including but not limited to 200 rpm, 220 rpm, 250 rpm, 280 rpm, 300 rpm, or any range between any two of the foregoing speeds; and a time of 4-5 hours, including but not limited to 4 hours, 4.5 hours, 5 hours, or any range between any two of the foregoing times. The first sieving includes passing through a 350-mesh sieve.

[0065] In some embodiments, the second mixing is performed at a speed of 1500-2000 rpm, including but not limited to 1500 rpm, 1600 rpm, 1700 rpm, 1800 rpm, 1900 rpm, 2000 rpm, or any range between any two of the foregoing speeds; and a time of 20-40 minutes, including but not limited to 20 minutes, 25 minutes, 30 minutes, 35 minutes, 40 minutes, or any range between any two of the foregoing times. The second mixing is performed under suitable conditions to ensure that the base material and the pyrolytic carbon source are thoroughly mixed.

[0066] In some embodiments, the second baking is performed at a temperature of 600-950°C, including but not limited to 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, 950°C, or any range between any two of the foregoing temperatures. The second baking is performed for a time period of 1-10h, including but not limited to 1h, 2h, 3h, 5h, 6h, 8h, or 10h, or any range between any two of the foregoing time periods. The second baking is performed under a protective gas, such as nitrogen, argon, or the like. Appropriate second baking conditions are used to ensure the coating effect of the carbon coating layer.

[0067] In some embodiments, the second mixing and the second baking are further followed by a second drying. The second drying is performed at a temperature of 80-120°C, including but not limited to 80°C, 90°C, 100°C, 110°C, 120°C, or any range between any two of the foregoing temperatures. The second drying is performed for a time period of 24-48h, including but not limited to 24h, 30h, 35h, 40h, 45h, 48h, or any range between any two of the foregoing time periods. The second drying is performed to remove water.

[0068] In some embodiments, the method further comprises sequentially performing a second crushing and a second screening on the material obtained from the second baking. The second crushing and the second screening are performed to obtain a silicon-carbon composite material with appropriate particle size. In some embodiments, the second crushing is performed at a rotational speed of 200-300rpm, including but not limited to 200rpm, 220rpm, 250rpm, 280rpm, 300rpm, or any range between any two of the foregoing rotational speeds. The second crushing is performed for a time period of 4-5h, including but not limited to 4h, 4.5h, 5h, or any range between any two of the foregoing time periods. The second screening comprises passing through a 350-mesh sieve.

[0069] In a preferred embodiment, the method for preparing the silicon-carbon negative electrode material comprises the following steps:

[0070] (a) mixing graphite, nano-silicon, a boron compound, and water to obtain a first mixture, wherein the first mixing is performed at a rotational speed of 1500-2000rpm and for a time period of 20-40min; drying the first mixture to obtain a first dried mixture, wherein the first drying is performed at a temperature of 80-120°C and for a time period of 24-48h; baking the first dried mixture to obtain a first baked mixture, wherein the first baking is performed under a protective gas and at a temperature of 300-600°C for a time period of 1-10h; and sequentially performing a first crushing and a first screening on the first baked mixture, wherein the first crushing is performed at a rotational speed of 200-300rpm and for a time period of 4-5h, and the first screening comprises passing through a 350-mesh sieve, thereby obtaining a base material.

[0071] (b) the substrate material is second mixed with the pyrolytic carbon source solution, the second mixing is at a speed of 1500-2000 rpm, and the second mixing is for 20-40 min; the second mixed material is second dried, the second drying is at a temperature of 80-120℃, and the second drying is for 24-48 h; the second dried material is second calcined, the second calcination is under a protective gas, the second calcination is at a temperature of 600-950℃, and the second calcination is for 1-10 h; the second calcined material is sequentially subjected to a second crushing treatment and a second screening treatment, the second crushing is at a speed of 200-300 rpm, and the second crushing is for 4-5 h, and the second screening treatment comprises: passing through a 350-mesh screen to obtain the silicon-carbon negative electrode material.

[0072] The silicon-carbon negative electrode material of the present application is shown in FIG. 1, which comprises a substrate 1 and a coating layer 2 coated on the surface of the substrate 1, the substrate 1 comprises an inner core 101 and a composite layer 102 on the surface of the inner core 101; the inner core 101 comprises graphite; the composite layer 103 comprises nano-silicon and boron oxide; and the coating layer 2 comprises nano-carbon.

[0073] According to another aspect of the present application, the present application also relates to a negative electrode sheet comprising the above-mentioned silicon-carbon negative electrode material or the silicon-carbon negative electrode material prepared by the above-mentioned preparation method.

[0074] The negative electrode sheet of the present application comprises a negative electrode current collector and a negative electrode layer on the surface of the negative electrode current collector; and the negative electrode material comprises the above-mentioned silicon-carbon negative electrode material.

[0075] According to another aspect of the present application, the present application also relates to a battery comprising the above-mentioned negative electrode sheet.

[0076] The battery of the present application has high initial efficiency, excellent cycle performance, rate performance and safety performance.

[0077] The battery of the present application comprises the above-mentioned negative electrode sheet, a positive electrode sheet, a separator and an electrolyte.

[0078] According to another aspect of the present application, the present application also relates to an electric device comprising the above-mentioned battery.

[0079] The electric device of the present application comprises an electric vehicle, a portable device and the like.

[0080] The present application is further explained and described in conjunction with specific examples and comparative examples.

[0081] Example 1

[0082] The present example provides a preparation method of a silicon-carbon negative electrode material, comprising the following steps:

[0083] (1) Put 15 g of nano-silicon powder, 85 g of graphite powder, 5 g of nano-boric acid powder and 150 g of deionized water into a vertical mixer for first mixing, the rotating speed of the first mixing is 1500 rpm, and the time is 20 min, then sieve (separate the material and grinding balls), and put the mixed material into a ceramic tray, and put the ceramic tray into a blast drying oven for first drying, the temperature of the first drying is 80℃, and the time is 24 h.

[0084] (2) Put the first dried material into a sagger, and put it into an atmosphere muffle furnace for first baking, and pass nitrogen as a protective gas, bake at 550℃ for 1 h, then take out, and then put it into a vertical mixer for first crushing.

[0085] (3) Sieve the first crushed material through a 350 mesh sieve to obtain a matrix material, put the matrix material into a double planetary mixer, and add a 5% PVDF solution according to a mass ratio of the matrix material to the PVDF of 1:2, then second mix at a rotating speed of 1500 rpm for 30 min. Put the slurry into a ceramic tray, and put it into a blast drying oven for second drying, the temperature is 80℃, and the drying time is 24 h.

[0086] (4) Put the second dried material into a sagger, and put it into an atmosphere muffle furnace for second baking, and pass nitrogen as a protective gas, carbonize at 800℃ for 5 h, cool down, take out, and put it into a high-speed mixer for second crushing, mix and crush at a rotating speed of 200 rpm for 30 min, take out, sieve through a 350 mesh sieve, and the silicon-carbon composite material is obtained.

[0087] Example 2

[0088] The embodiment provides a preparation method of a silicon-carbon negative electrode material, including the following steps:

[0089] (1) Put 15 g of nano-silicon powder, 85 g of graphite powder, 5 g of nano-boric acid powder and 150 g of deionized water into a vertical mixer for first mixing, the rotating speed of the first mixing is 1500 rpm, and the time is 30 min, then sieve (separate the material and grinding balls), and put the mixed material into a ceramic tray, and put the ceramic tray into a blast drying oven for first drying, the temperature of the first drying is 80℃, and the time is 24 h.

[0090] (2) Put the first dried material into a sagger, and put it into an atmosphere muffle furnace for first baking, and pass nitrogen as a protective gas, bake at 550℃ for 2 h, then take out, and then put it into a vertical mixer for first crushing.

[0091] (3) The first crushed material is sieved through a 350-mesh sieve to obtain a base material. The base material is placed in a double planetary mixer, and a 5% PVDF solution is added in a mass ratio of 1:3 between the base material and the PVDF solution. Then, first mixing is performed at a speed of 2000 rpm for 30 min. The slurry is placed in a ceramic tray and subjected to second drying in a blast drying oven at a temperature of 80°C for 24 h.

[0092] (4) The second dried material is placed in a sagger and subjected to second calcination in an atmosphere muffle furnace. Nitrogen gas is introduced as a protective gas, and carbonization is performed at 700°C for 5 h. After cooling, the material is taken out and subjected to second crushing treatment in a high-speed mixer at a speed of 250 rpm for 30 min. The material is sieved through a 350-mesh sieve to obtain a silicon-carbon composite material.

[0093] Example 3

[0094] The present embodiment provides a method for preparing a silicon-carbon negative electrode material, which comprises the following steps:

[0095] (1) 15 g of nano-silicon powder, 85 g of graphite powder, 5 g of nano-boric acid powder, and 150 g of deionized water are added to a vertical mixer for first mixing at a speed of 1500 rpm for 30 min. Then, the material and grinding balls are separated by sieving. The obtained mixture is placed in a ceramic tray and subjected to first drying in a blast drying oven at a temperature of 80°C for 48 h.

[0096] (2) The first dried material is placed in a sagger and subjected to first calcination in an atmosphere muffle furnace. Nitrogen gas is introduced as a protective gas, and calcination is performed at 550°C for 2 h. Then, the material is taken out and subjected to first crushing treatment in a vertical mixer.

[0097] (3) The first crushed material is sieved through a 350-mesh sieve to obtain a base material. The base material is placed in a double planetary mixer, and a 5% PVDF solution is added in a mass ratio of 1:3 between the base material and the PVDF solution. Then, first mixing is performed at a speed of 2000 rpm for 30 min. The slurry is placed in a ceramic tray and subjected to second drying in a blast drying oven at a temperature of 80°C for 24 h.

[0098] (4) The second dried material is placed in a sagger and subjected to second calcination in an atmosphere muffle furnace. Nitrogen gas is introduced as a protective gas, and carbonization is performed at 700°C for 5 h. After cooling, the material is taken out and subjected to second crushing treatment in a high-speed mixer at a speed of 250 rpm for 30 min. The material is sieved through a 350-mesh sieve to obtain a silicon-carbon composite material.

[0099] Example 4

[0100] The embodiment provides a preparation method of a silicon-carbon negative electrode material, and comprises the following steps:

[0101] (1) 15 g of nano-silicon powder, 85 g of graphite powder, 5 g of nano-boric acid powder and 150 g of deionized water are added into a vertical mixer for first mixing, the rotating speed is 1500 rpm, and after mixing for 30 min, the mixture is sieved, the sieved mixture is placed into a ceramic tray, and the ceramic tray is placed into a blast drying oven for first drying, the temperature is 80 DEG C, and the drying is performed for 24 h.

[0102] (2) The first dried material is loaded into a sagger, and is placed into an atmosphere muffle furnace for first calcination, nitrogen gas is introduced as a protective gas, the material is calcined at 550 DEG C for 2 h, then is taken out, and is placed into a vertical mixer for first crushing.

[0103] (3) The first crushed material is sieved through a 350-mesh sieve to obtain a base material, the base material is placed into a double-planetary mixer, and a starch solution obtained by low-temperature gelatinization is added according to a mass ratio of the base material to the starch of 5:4, the mass fraction of the starch in the starch solution is 6 %, then second mixing is performed, the rotating speed is 2000 rpm, and the stirring is performed for 30 min. The slurry is placed into a ceramic tray, and is placed into a blast drying oven for second drying, the temperature is 80 DEG C, and the drying is performed for 24 h.

[0104] (4) The second dried material is loaded into a sagger, and is placed into an atmosphere muffle furnace for second calcination, nitrogen gas is introduced as a protective gas, the material is carbonized at 700 DEG C for 5 h, is cooled and taken out, is placed into a high-speed mixer for second crushing treatment, and is mixed and crushed at a rotating speed of 300 rpm for 30 min, and then is taken out and sieved through a 350-mesh sieve, so that a silicon-carbon composite material is obtained.

[0105] Comparative Example 1

[0106] The comparative example provides a preparation method of a silicon-carbon negative electrode material, and comprises the following steps:

[0107] 15 g of nano-silicon powder and 85 g of graphite powder are mixed by using a mixer at a rotating speed of 1500 rpm for 20 min to obtain a premixed material, then 5 % of a PVDF solution is added according to a mass ratio of the material to the PVDF of 1:2, and mixing and stirring are performed for 30 min. The obtained slurry is placed into a ceramic tray, and is placed into a blast drying oven for drying at 80 DEG C for 24 h. The dried material is loaded into a sagger, is placed into an atmosphere muffle furnace, nitrogen gas is introduced as a protective gas, the material is carbonized at 800 DEG C for 5 h, is cooled and taken out, is placed into a high-speed mixer, is mixed and crushed at a rotating speed of 200 rpm for 30 min, then is taken out and sieved through a 350-mesh sieve, and a silicon-carbon composite material is obtained.

[0108] Experimental Example

[0109] The silicon-carbon negative electrode material obtained in each example and the comparative example was used to prepare a battery, specifically including: mixing the materials with the solvent NMP in a ratio of silicon-carbon negative electrode material: SuperP: PVDF = 8:1:1 to obtain a negative electrode slurry, coating the negative electrode slurry on a copper foil, and drying to obtain a negative electrode sheet; using metal lithium as the counter electrode; using a 1 mol / L LiPF6 solution as the electrolyte, and using EC, DEC and DMC as the solvent, with a volume ratio of EC:DEC:DMC = 1:1:1; preparing a 2032 button cell and detecting the electrochemical performance. Test conditions: 25°C, 0.1C, 0.05-2.5V.

[0110] The results of the chemical performance test of the battery are shown in Table 1.

[0111] Table 1: Results of the electrochemical performance test of the battery

[0112] As can be seen from Table 1 above, the battery prepared from the silicon-carbon negative electrode material obtained by the method of each example of the application has excellent initial specific discharge capacity and initial coulombic efficiency, with an initial specific discharge capacity of 440 mAh / g and an initial coulombic efficiency of 79% or more.

[0113] The initial coulombic efficiency of the battery prepared from the silicon-carbon negative electrode material obtained by the method of Comparative Examples 1-3 is relatively poor.

[0114] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the application, and not to limit them; although the application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that they can still modify the technical solutions described in the foregoing examples, or make equivalent substitutions for part or all of the technical features; and these modifications or substitutions do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the examples of the application. Industrial applicability

[0115] The silicon-carbon negative electrode material of the application uses graphite as the core, and boron oxide uniformly adheres the nanosilicon to the surface of the graphite, which can improve the adhesion of the nanosilicon and the graphite, and avoid the silicon material from falling off the surface of the graphite during the charging and discharging process; the nanocarbon coating layer can avoid the occurrence of side reactions between the silicon particles and the electrolyte, and can also increase the electronic conductivity of the silicon-carbon negative electrode material; the silicon-carbon negative electrode material of the application has excellent comprehensive electrochemical performance.

Claims

1. A silicon-carbon anode material, characterized in that, It includes a matrix and a coating layer covering the surface of the matrix, wherein the matrix includes a core and a composite layer located on the surface of the core; The core contains graphite; The composite layer comprises nano-silicon and boron oxide; The coating layer contains nano-carbon.

2. The silicon-carbon anode material according to claim 1, characterized in that, The graphite comprises spherical graphite.

3. The silicon-carbon anode material according to claim 1, characterized in that, The battery prepared from the silicon-carbon anode material exhibits an initial discharge specific capacity of over 440 mAh / g under test conditions of 25°C, 0.1C, and 0.05–2.5V. The initial coulombic efficiency of the battery prepared from the silicon-carbon anode material is 79% or higher.

4. The method for preparing the silicon-carbon anode material according to any one of claims 1 to 3, characterized in that, Includes the following steps: Graphite, nano-silicon, boron compound and water are first mixed and first calcined to obtain a matrix material; the matrix material is then second mixed and second calcined with a pyrolytic carbon source solution to obtain a silicon-carbon anode material.

5. The method for preparing the silicon-carbon anode material according to claim 4, characterized in that, It includes at least one of the following features (1) to (6): (1) The boron compound comprises at least one of boron oxide and boric acid; (2) The pyrolytic carbon source solution includes a pyrolytic carbon source and water, wherein the pyrolytic carbon source accounts for 5% to 8% of the mass content of the pyrolytic carbon source solution; the pyrolytic carbon source includes water-soluble carbon source and / or non-water-soluble carbon source; (3) The mass ratio of the nano-silicon to the graphite is x:(1-x), where 0 <x≤0.4; (4) The mass ratio of boron in the boron compound to the total mass of nano-silicon and graphite is y:1, where 0 <y≤0.1; (5) The mass ratio of the boron compound to the water is 1:(30-40); (6) The mass ratio of the pyrolytic carbon source in the pyrolytic carbon source solution to the matrix material is (2-6):(1-5).

6. The method for preparing the silicon-carbon anode material according to claim 4, characterized in that, It includes at least one of the following features (1) to (3): (1) The rotation speed of the first mixing is 1500-2000 rpm, and the mixing time is 20-40 min; (2) The temperature of the first roasting is 300-600℃, and the time of the first roasting is 1-10h; (3) The first calcination is carried out under protective gas conditions.

7. The method for preparing the silicon-carbon anode material according to claim 4, characterized in that, It includes at least one of the following features (1) to (5): (1) A first drying process is further included between the first mixing and the first calcination; (2) The temperature of the first drying is 80-120℃, and the drying time is 24-48h; (3) It also includes: sequentially performing a first crushing process and a first screening process on the first roasted material; (4) The rotation speed of the first crushing process is 200-300 rpm, and the time of the first crushing process is 4-5 h; (5) The first screening process includes: passing through a 350-mesh sieve.

8. The method for preparing the silicon-carbon anode material according to claim 4, characterized in that, It includes at least one of the following features (1) to (3): (1) The rotation speed of the second mixing is 1500-2000 rpm, and the mixing time is 20-40 min; (2) The temperature of the second roasting is 600-950℃, and the roasting time is 1-10h; (3) The second calcination is carried out under a protective gas condition.

9. The method for preparing the silicon-carbon anode material according to claim 4, characterized in that, It includes at least one of the following features (1) to (5): (1) A second drying process is further included between the second mixing and the second calcination; (2) The temperature of the second drying is 80-120℃, and the drying time is 24-48h; (3) It also includes: subjecting the material obtained from the second roasting to a second crushing process and a second screening process in sequence; (4) The second crushing speed is 200-300 rpm, and the second crushing time is 4-5 h; (5) The second screening process includes: passing through a 350-mesh sieve.

10. A negative electrode sheet, characterized in that, The silicon-carbon anode material includes any one of claims 1 to 3, or the silicon-carbon anode material prepared by the preparation method of any one of claims 4 to 9.

11. A battery, characterized in that, Includes the negative electrode sheet as described in claim 10.

12. An electrical appliance, characterized in that, Includes the battery as described in claim 11.

Images