CN110429272B - Silicon-carbon composite negative electrode material with pitaya-like structure and preparation method thereof - Google Patents
Silicon-carbon composite negative electrode material with pitaya-like structure and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a preparation method of a silicon-carbon composite anode material with a dragon fruit-like structure, which comprises the following steps: s1: mixing graphite powder, nano-scale silicon powder or micro-nano-scale silicon powder, a conductive agent and a binder by a dry method; s2: performing wet dispersion on the material obtained in the step S1; s3: drying the material obtained in the step S2; s4: cold press molding the material obtained in the step S3; s5: carbonizing the material obtained in the step S4 at high temperature; s6: crushing and grading the material obtained in the step S5; s7: coating and granulating the material obtained in the step S6; s8: performing secondary high-temperature carbonization on the material obtained in the step S7; s9: and (5) screening the material obtained in the step (S8) to obtain the structural dragon fruit type silicon-carbon composite anode material. The invention enhances the structural strength of the shell layer of the silicon-carbon composite material, realizes complete and uniform coating of nano/micro nano particles, has better circulation stability, and meets the application requirement of high-performance negative electrodes in lithium ion batteries.
Description
Technical Field
The invention belongs to the technical field of lithium ion batteries, and particularly relates to a silicon-carbon composite negative electrode material with a pitaya-like structure and a preparation method of the silicon-carbon composite negative electrode material.
Background
The lithium ion battery is a new battery widely applied to the industries of rail transit, electronic communication, wearable equipment and the like. The existing lithium ion battery cathode material mainly adopts natural graphite, artificial graphite and middle equal graphite materials. After years of research, the graphite negative electrode material basically reaches the theoretical specific capacity of 372mAh/g, but still cannot meet the actual requirement. The theoretical lithium storage capacity of the silicon material is up to 4200mAh/g, and the silicon material has lower lithium intercalation potential and abundant reserves. However, pure silicon powder has poor conductivity, generates large volume expansion when Li-Si combination is formed, and causes electrode structure collapse and active material drop due to volume drastic change in the charging and discharging process, so that the cycle performance of the pole piece is reduced, and the method cannot be practically applied. If the silicon-carbon composite material is used as the negative electrode material of the lithium ion battery, the defect of low energy density of the carbon material can be made up by the silicon material, and meanwhile, the defect of poor conductivity of the silicon material and the defect of inhibition of volume expansion of silicon can be made up by the carbon material. But the existing carbon-silicon composite material has the defects of poor shell structure strength and poor cycle stability. The reason for this is that the shell layer structure of the conventional silicon carbon material is prepared by simple coating, so that the conditions of uneven or incomplete coating exist, the silicon material is exposed, the volume of the silicon material is repeatedly changed due to frequent contact with the electrolyte, the shell layer is collapsed, and the cycle stability is rapidly reduced. Therefore, how to develop a novel silicon-carbon composite material can enhance the structural strength of the shell layer thereof, improve the conductivity thereof, and relieve the volume expansion of silicon powder in the charging and discharging process, so that the silicon-carbon composite material has better cycle stability, can meet the application requirements of high-performance negative electrode materials, and is the direction of research of technical personnel in the field.
Disclosure of Invention
The invention aims to provide a silicon-carbon composite negative electrode material which has higher surface shell strength and better conductivity, can relieve the volume expansion of silicon powder in the charging and discharging process, has better cycle stability and meets the application requirement of serving as a high-performance negative electrode of a lithium ion battery.
The technical scheme is as follows:
a preparation method of a silicon-carbon composite negative electrode material with a pitaya-like structure comprises the following steps: s1: mixing graphite powder, nano-scale silicon powder or micro-nano-scale silicon powder, a conductive agent and a binder by a dry method; the graphite powder is any one of artificial graphite, natural graphite and intermediate phase graphite; the conductive agent is any one of acetylene black, carbon fiber, Ketjen black and carbon nano tube; the binder adopts asphalt powder or resin; s2: performing wet dispersion processing on the material obtained in the step S1; s3: drying the material obtained in the step S2; s4: cold press molding the material obtained in the step S3; s5: carrying out high-temperature carbonization processing on the material obtained in the step S4; s6: crushing and grading the material obtained in the step S5; s7: coating and granulating the material obtained in the step S6; s8: carrying out secondary high-temperature carbonization processing on the material obtained in the step S7; s9: and (5) screening the material obtained in the step (S8) to obtain the silicon-carbon composite anode material with a pitaya-like structure.
By adopting the technical scheme: firstly, crushing and mixing graphite powder, nanoscale silicon powder or micro-nanoscale silicon powder, a conductive agent and a binder by a high-energy ball mill, crushing, uniformly dispersing and mixing particles, and forming a whole block by compression molding and high-temperature carbonization and bonding. Then the mixture is pre-crushed by a jaw crusher and milled by air flow for secondary granulation. The shell layer of the amorphous carbon coating layer is formed, graphite particles are filled in the shell layer, and the nano silicon particles are distributed in the graphite particles.
Preferably, in the preparation method of the silicon-carbon composite anode material with the pitaya-like structure, the method comprises the following steps: the dry mixing process of step S1 includes the following steps: s11: mixing graphite powder, nanoscale silicon powder or micro-nanoscale silicon powder, a conductive agent and a binder, and then putting into a high-energy ball milling tank; s12: keeping an inert environment in the high-energy ball milling tank body; s13: the mixture of graphite powder, nano-scale silicon powder or micro-nano-scale silicon powder, the conductive agent and the binder is continuously ball-milled and mixed for 8 to 24 hours at the rotating speed of 450-900 r/min.
By adopting the technical scheme: mechanical grinding is realized by high-energy ball milling, the particle sizes of graphite and silicon can be reduced, electrical contact is increased, and meanwhile, different particles can be fully mixed together by the mechanical ball milling, namely, nanoscale or micro-nanoscale silicon particles are fully embedded into a graphite layer in the ball milling process, so that the volume expansion of silicon in the charging and discharging process is favorably inhibited, and the electrochemical performance of the material is improved.
More preferably, in the preparation method of the silicon-carbon composite anode material with the pitaya-like structure, the method comprises the following steps: step S12 includes the following steps: s121: spraying and wetting the high-energy ball milling tank by absolute ethyl alcohol; s122: vacuumizing the high-energy ball milling tank; s123: replacing high-purity nitrogen into a high-energy ball milling tank; s124: jump back to S122, loop three times.
By adopting the technical scheme: before the high-energy ball mill is vacuumized, the graphite powder, the nanoscale silicon powder or the micro-nanoscale silicon powder, the conductive agent and the binder are attached to the inner wall of the tank body by spraying and wetting with absolute ethyl alcohol, so that the graphite powder, the nanoscale silicon powder or the micro-nanoscale silicon powder, the conductive agent and the binder are effectively prevented from being pumped away together in the vacuumizing process.
Further preferably, in the preparation method of the silicon-carbon composite anode material with a pitaya-like structure, the method comprises the following steps: particle size distribution D of graphite powder in step S1505-18um, the particle size distribution D50 of the nano-grade silicon powder or micro-nano-grade silicon powder is 50-800nm, the particle size distribution D50 of the conductive agent is 30-45nm, and the particle size distribution D50 of the binder is 20-60 um; the mass percentage of the graphite powder to the silicon-carbon composite negative electrode material with the dragon fruit-like structure is 45-80%, the mass percentage of the nano-scale silicon powder or micro-nano-scale silicon powder to the silicon-carbon composite negative electrode material with the dragon fruit-like structure is 10-40%, the mass percentage of the conductive agent to the silicon-carbon composite negative electrode material with the dragon fruit-like structure is 1-2%, and the mass percentage of the binder to the silicon-carbon composite negative electrode material with the dragon fruit-like structure is 8-14%.
Preferably, in the preparation method of the silicon-carbon composite anode material with the pitaya-like structure, the method comprises the following steps: the wet dispersion process of step S2 includes the steps of: s21: adding the material obtained in the step S1 into a solution containing 1% -3% of CMC dispersant to enable the solid content of the solution to reach 45% -60%; s22: and continuously stirring the solution of the S13 for 8-10h by using a planetary stirrer.
Preferably, in the preparation method of the silicon-carbon composite anode material with the pitaya-like structure, the method comprises the following steps: step S3 includes: and (5) putting the material obtained in the step S2 into a vacuum drying oven, and performing vacuum drying in a temperature environment of 60-90 ℃ until the solvent is completely evaporated.
Preferably, in the preparation method of the silicon-carbon composite anode material with the pitaya-like structure, the method comprises the following steps: step S4 includes: and (5) putting the material obtained in the step (S3) into a mould, and pressing for 10-30 minutes in a compression molding or isostatic pressing mode under the pressure environment of 20-50 MPa.
Preferably, in the preparation method of the silicon-carbon composite anode material with the pitaya-like structure, the method comprises the following steps: step S6 includes the steps of: s61: pre-crushing the material obtained in the step S5 by using a jaw crusher; s62: and (4) crushing and grading the material obtained in the step (S61) by using a jet mill.
Preferably, in the preparation method of the silicon-carbon composite anode material with the pitaya-like structure, the method comprises the following steps: the high-temperature carbonization processing in the steps S5 and S8 is realized by a carbonization furnace; and step S7, the coating and granulating process is realized by a mechanical fusion machine.
The invention also discloses a silicon-carbon composite negative electrode material: the silicon-carbon composite negative electrode material is prepared by adopting the preparation method of any one of the silicon-carbon composite negative electrode materials.
Compared with the prior art, the invention forms the silicon material, the graphite and the binder into a whole by primary ball-milling coating carbonization, then forms a layer-to-layer structure mode similar to dragon fruit by secondary crushing into proper granularity and coating the crushed and exposed part by secondary coating carbonization, thereby obtaining stronger shell structure strength and better conductivity compared with the existing product, ensuring that the volume expansion of silicon particles in the charging and discharging process can be relieved, and having better electrochemical cycle stability.
Drawings
FIG. 1 is a process flow diagram of the present invention;
FIG. 2 is a schematic cross-sectional view of a silicon-carbon composite negative electrode material according to the present invention;
fig. 3 is a charge-discharge curve diagram of a button lithium ion battery formed by the product obtained in example 4 as a negative electrode sheet, 1M LiPF6 (DMC: EC: 1 vol%) as an electrolyte and a polypropylene film as a diaphragm at a current density of 0.5C;
fig. 4 is a coulombic efficiency chart at a current density of 0.5C for a lithium ion battery of a button type having the product obtained in example 4 as a negative electrode tab, 1M LiPF6 (DMC: EC: 1 vol%) as an electrolyte, and a polypropylene film as a separator.
The correspondence between each reference numeral and the part name is as follows:
1. graphite particles; 2. nano-scale silicon particles or micro-nano-scale silicon particles; 3. an amorphous carbon coating.
Detailed Description
In order to more clearly illustrate the technical solution of the present invention, the following will further describe various embodiments with reference to fig. 1. It is to be understood that the practice of the invention is not limited to the following examples, and that any changes and/or modifications may be made thereto without departing from the scope of the invention. In the following examples, all percentages are by weight unless otherwise specified, and the equipment and materials used are commercially available or commonly used in the art. The methods in the following examples are conventional in the art unless otherwise specified.
Example 1: a preparation method of a silicon-carbon composite negative electrode material comprises the following steps:
s1: at normal temperature, the artificial graphite powder (D) is mixed505um) and micro-nano silicon powder (D)50800nm) and acetylene black (D)5030nm) and resin powder (D)5020um) is mixed with 1kg in a ratio of 80:10:1:9, added into a high-energy ball milling tank, and then the inside of the tank body is subjected to vacuum-high-purity nitrogen replacement for 3 times, so as to ensure the inert environment in the tank. During the vacuum pumping, in order to prevent the dry mixed materials from being pumped away, the mixed materials are sprayed and wetted by absolute ethyl alcohol before the vacuum pumping. And then carrying out high-energy ball milling and mixing, wherein the ball milling time is controlled for 8 hours, and the speed is controlled at 450 r/min, so as to obtain a material A.
S2: and (5) adding the material A obtained in the step S1 into a solution prepared with a 1% CMC dispersant, wherein the solid content is controlled at 45%. The stirring time is controlled to be 8h, and a material B is obtained.
S3: and (5) placing the material B obtained in the step (S2) in a vacuum drying oven, controlling the temperature in the oven body to be 60 ℃, and completely evaporating the solvent to obtain a material C.
S4: and (5) placing the material C obtained in the step (S3) in a mould, controlling the pressure at 20MPa and the time at 10 minutes to obtain a material D.
S5: and (4) placing the material D obtained in the step S4 in an inert gas carbonization furnace. Controlling the highest carbonization temperature at 850 ℃, and keeping the temperature for 2 hours to obtain a material E.
S6: and (5) pre-crushing the material E obtained in the step (S5) to below 2mm by using a jaw crusher, and then crushing and grading the material E by using an air flow mill until the granularity D50 reaches 10um to obtain a material F.
S7: in the material F obtained in step S6, 6% of high-temperature asphalt powder was added. Stirring and mixing for 2h by a mechanical fusion machine to obtain a material G.
S8: and (5) putting the material G obtained in the step (S7) into a carbonization furnace protected by high-temperature inert gas, wherein the carbonization process conditions are the same as those in the step (S5), so as to obtain a material H.
S9: and (5) sieving the material H obtained in the step (S8) by using a 300-mesh sieve to obtain the silicon-carbon composite anode material with a pitaya-like structure, and evaluating related physical properties and electrochemical properties.
Example 2: a preparation method of a silicon-carbon composite negative electrode material comprises the following steps:
s1: at normal temperature, the artificial graphite powder (D) is mixed505um) and micro-nano silicon powder (D)50400nm) and acetylene black (D)5030nm) and resin powder (D)5020um) is mixed with 1kg according to the proportion of 75:15:2:8, and then the mixture is added into a high-energy ball milling tank, and then the inside of the tank body is subjected to vacuum-high-purity nitrogen replacement for 3 times, so that the inert environment in the tank is ensured. During the vacuum pumping, in order to prevent the dry-mixed materials from being pumped away, the dry-mixed materials can be sprayed and wetted by absolute ethyl alcohol before the vacuum pumping. Then high-energy ball milling and mixing are carried out, the ball milling time is controlled for 10 hours, and the speed is controlled at 500 r/min. To obtain a material A.
S2: and (5) adding the material A obtained in the step S1 into a solution prepared with 1.5% of CMC dispersant, wherein the solid content is controlled at 45%. The stirring time is controlled at 8h, and a material B is obtained.
S3: and (5) placing the material B obtained in the step S2 in a vacuum drying oven, and controlling the temperature at 60 ℃ until the solvent is completely evaporated to obtain a material C.
S4: and (5) placing the material C obtained in the step (S3) in a mould, controlling the pressure at 50MPa and the time at 20 minutes to obtain a material D.
S5: and (4) placing the material D obtained in the step S4 in an inert gas carbonization furnace. Controlling the highest carbonization temperature at 850 ℃, and keeping the temperature for 2 hours to obtain a material E.
S6: pre-crushing the material E obtained in the step S5 to below 2mm by using a jaw crusher, and then crushing and grading by using an air flow mill until the granularity D50 reaches 10um to obtain a material F.
S7: in the material F obtained in step S6, 6% of high-temperature asphalt powder was added. Stirring and mixing for 2h by a mechanical fusion machine to obtain a material G.
S8: and (5) putting the material G obtained in the step (S7) into a carbonization furnace protected by high-temperature inert gas, wherein the carbonization process conditions are the same as those in the step (S5), so as to obtain a material H.
S9: and (5) sieving the material H obtained in the step (S8) by using a 300-mesh sieve to obtain the silicon-carbon composite anode material with a pitaya-like structure, and evaluating related physical properties and electrochemical properties.
Example 3: a preparation method of a silicon-carbon composite negative electrode material comprises the following steps:
s1: at normal temperature, the artificial graphite powder (D) is mixed5010um), nano-level silicon powder or micro-nano-level silicon powder (D)50100nm), acetylene black (D)5030nm) and high-temperature asphalt powder (D)5020um) is mixed with 1kg according to the ratio of 65:20:1:14, added into a high-energy ball milling tank, and then the interior of the tank body is subjected to vacuum-high-purity nitrogen replacement for 3 times, so as to ensure the inert environment in the tank. During the vacuum pumping, in order to prevent the dry mixed materials from being pumped away, the mixed materials can be sprayed and wetted by absolute ethyl alcohol before the vacuum pumping. Then high-energy ball milling and mixing are carried out, the ball milling time is controlled for 10 hours, and the speed is controlled at 600 r/min. To obtain a material A.
S2: and (5) adding the material A obtained in the step S1 into a solution prepared with 1.5% of CMC dispersant, wherein the solid content is controlled at 60%. The stirring time is controlled to be 8h, and a material B is obtained.
S3: and (5) placing the material B obtained in the step S2 in a vacuum drying oven, and controlling the temperature at 70 ℃ until the solvent is completely evaporated to obtain a material C.
S4: and (5) placing the material C obtained in the step (S3) in a mould, controlling the pressure at 20MPa and the time at 10 minutes to obtain a material D.
S5: and (4) placing the material D obtained in the step S4 in an inert gas carbonization furnace. Controlling the highest carbonization temperature at 950 ℃, and preserving the temperature for 2 hours to obtain a material E.
S6: and (5) pre-crushing the material E obtained in the step (S5) to below 2mm by using a jaw crusher, and then crushing and grading the material E by using an air flow mill until the granularity D50 reaches 10um to obtain a material F.
S7: in the material F obtained in step S6, 8% of high-temperature asphalt powder was added. Stirring and mixing for 4 hours by a mechanical fusion machine to obtain a material G.
S8: and (5) putting the material G obtained in the step (S7) into a carbonization furnace protected by high-temperature inert gas, wherein the carbonization process conditions are the same as those in the step (S5), so as to obtain a material H.
S9: and (5) sieving the material H obtained in the step (S8) by using a 300-mesh sieve to obtain the silicon-carbon composite anode material with a pitaya-like structure, and evaluating related physical properties and electrochemical properties.
Example 4: a preparation method of a silicon-carbon composite negative electrode material comprises the following steps:
s1: at normal temperature, natural graphite powder (D)5015um), nanoscale silicon powder or micro-nanoscale silicon powder (D)5070nm) and acetylene black (D)5045nm), high-temperature asphalt powder (D)5060um) is mixed with 1kg according to the proportion of 60:25:2:13, added into a high-energy ball milling tank, and then the interior of the tank body is subjected to vacuum-high-purity nitrogen replacement for 3 times, so as to ensure the inert environment in the tank. During the vacuum pumping, in order to prevent the dry mixed materials from being pumped away, the mixed materials can be sprayed and wetted by absolute ethyl alcohol before the vacuum pumping. Then high-energy ball milling and mixing are carried out, the ball milling time is controlled for 8 hours, and the speed is controlled at 450 r/min. To obtain a material A.
And S2, adding the material A obtained in the step S1 into a solution prepared with a 2% CMC dispersant, wherein the solid content is controlled to be 55%. The stirring time is controlled at 9h, and a mixed material B is obtained.
S3: and (5) placing the material B obtained in the step S2 in a vacuum drying oven, and controlling the temperature at 80 ℃ until the solvent is completely evaporated to obtain a material C.
S4: and (5) placing the material C obtained in the step (S3) in a mould, controlling the pressure at 30MPa and the time at 10 minutes to obtain a material D.
S5: and (4) placing the material D obtained in the step S4 in an inert gas carbonization furnace. Controlling the highest carbonization temperature at 950 ℃, and preserving the temperature for 3 hours to obtain a material E.
S6: pre-crushing the material E obtained in the step S5 to below 2mm by using a jaw crusher, and then crushing and grading the material E by using an air flow mill until the granularity D50 reaches 10um to obtain a material F.
S7: in the material F obtained in step S6, 8% of high-temperature asphalt powder was added. Stirring and mixing for 2h by a mechanical fusion machine to obtain a material G.
S8: and (5) putting the material G obtained in the step (S7) into a carbonization furnace protected by high-temperature inert gas, wherein the carbonization process conditions are the same as those in the step (S5), so as to obtain a material H.
S9: and (5) sieving the material H obtained in the step (S8) by using a 300-mesh sieve to obtain the silicon-carbon composite anode material with a pitaya-like structure, and evaluating related physical properties and electrochemical properties.
Example 5: a preparation method of a silicon-carbon composite negative electrode material comprises the following steps:
s1: at normal temperature, the artificial graphite powder (D) is mixed505um), nanoscale silicon powder or micro-nanoscale silicon powder (D)5050nm) of acetylene black (D)5045nm) and high-temperature asphalt powder (D)5020um) is mixed with 1kg according to the ratio of 55:30:2:13, added into a high-energy ball milling tank, and then the inside of the tank body is subjected to vacuum-high-purity nitrogen replacement for 3 times, so as to ensure the inert environment in the tank. During the vacuum pumping, in order to prevent the dry mixed materials from being pumped away, the mixed materials can be sprayed and wetted by absolute ethyl alcohol before the vacuum pumping. Then high-energy ball milling and mixing are carried out, the ball milling time is controlled for 8 hours, and the speed is controlled at 450 r/min. To obtain a material A.
S2: and (5) adding the material A obtained in the step S1 into a solution prepared with a 1% CMC dispersant, wherein the solid content is controlled at 45%. The stirring time is controlled to be 8h, and a material B is obtained.
S3: and (5) placing the material B obtained in the step S2 in a vacuum drying oven, and controlling the temperature at 80 ℃ until the solvent is completely evaporated to obtain a material C.
S4: and (5) placing the material C obtained in the step (S3) in a mould, controlling the pressure at 40MPa and the time at 20 minutes to obtain a material D.
S5: and (4) placing the material D obtained in the step S4 in an inert gas carbonization furnace. Controlling the highest carbonization temperature at 1000 ℃, and preserving the heat for 2 hours to obtain a material E.
S6: and (5) pre-crushing the material E obtained in the step (S5) to below 2mm by using a jaw crusher, and then crushing and grading the material E by using an air flow mill until the granularity D50 reaches 12um to obtain a material F.
S7: in the material F obtained in step S6, 10% of high-temperature asphalt powder was added. Stirring and mixing for 2h by a mechanical fusion machine to obtain a material G.
S8: and (5) putting the material G obtained in the step (S7) into a carbonization furnace protected by high-temperature inert gas, and obtaining a material H under the same carbonization process conditions as in the step (S5).
S9: and (5) sieving the material H obtained in the step (S8) by using a 300-mesh sieve to obtain the silicon-carbon composite anode material with a pitaya-like structure, and evaluating related physical properties and electrochemical properties.
Example 6: a preparation method of a silicon-carbon composite negative electrode material comprises the following steps:
s1: under the condition of normal temperature, the raw material mesophase stone ink powder (D)5018um), nano-level silicon powder or micro-nano-level silicon powder (D)50100nm), acetylene black (D)5045nm), resin powder (D)5060um) is mixed with 1kg according to the proportion of 45:40:1:14, added into a high-energy ball milling tank, and then the interior of the tank body is subjected to vacuum-high-purity nitrogen replacement for 3 times, so as to ensure the inert environment in the tank. During the vacuum pumping, in order to prevent the dry mixed materials from being pumped away, the mixed materials can be sprayed and wetted by absolute ethyl alcohol before the vacuum pumping. And then carrying out high-energy ball milling and mixing, wherein the ball milling time is controlled for 24 hours, and the speed is controlled at 900 r/min, so as to obtain a material A.
S2: and (4) adding the material A obtained in the step S1 into a solution prepared with a 3% CMC dispersant, wherein the solid content is controlled at 60%. The stirring time is controlled to be 10h, and a material B is obtained.
S3: and (5) putting the material B obtained in the step (S2) into a vacuum drying oven, controlling the temperature at 90 ℃, and completely evaporating the solvent to obtain a material C.
S4: and (5) placing the material C obtained in the step (S3) in a mould, controlling the pressure at 50MPa and the time at 30 minutes to obtain a material D.
S5: and (5) placing the material D obtained in the step S4 in an inert gas carbonization furnace. Controlling the highest carbonization temperature at 1000 ℃, and preserving the heat for 4 hours to obtain a material E.
S6: and (5) pre-crushing the material E obtained in the step (S5) to below 2mm by using a jaw crusher, and crushing and grading the material E by using an air flow mill until the granularity D50 reaches 15um to obtain a material F.
S7: in the material F obtained in step S6, 12% of high-temperature asphalt powder was added. Stirring and mixing for 6h by a mechanical fusion machine to obtain a material G.
S8: and (5) putting the material G obtained in the step (S7) into a carbonization furnace protected by high-temperature inert gas, wherein the carbonization process conditions are the same as those in the step (S5), so as to obtain a material H.
S9: and (5) sieving the material H obtained in the step (S8) by using a 300-mesh sieve to obtain the silicon-carbon composite anode material with a pitaya-like structure, and evaluating related physical properties and electrochemical properties.
Button cell testing was performed on the products obtained in examples 1-6: and (3) uniformly mixing the silicon-carbon composite negative electrode material prepared in each embodiment, conductive carbon black, CMC and SBR according to a ratio of 94:1.5:2:2.5, coating the mixture on a copper foil, and putting the coated pole piece into a vacuum drying oven at the temperature of 80 ℃ for vacuum drying for 6 hours for later use. The simulated battery is assembled in a German Braun glove box charged with hydrogen, the electrolyte is 1MLiPF6+ EC: DEC: DMC: 1:1 (volume ratio), the metal lithium sheet is a counter electrode, the electrochemical performance test is carried out on a Wuhan blue battery tester, the charging and discharging voltage range is 0.005V to 2V, and the charging and discharging rate is 0.1C. The test data is shown in table 1 below:
TABLE 1
The data in table 1 show that the silicon-carbon composite material obtained by the invention has higher first coulombic efficiency and specific discharge capacity, particularly, in example 4, the specific discharge capacity is 1172.1mAh/g, the first coulombic efficiency is 90.1%, and the 100-time cyclic coulombic efficiency is still kept above 99.5%. The structure of the pitaya-like silicon-carbon composite material has stronger structural strength of a carbon shell layer, and the nano/micro-nano particles are completely and uniformly coated, so that the pitaya-like silicon-carbon composite material has better electrochemical cycle stability.
The above description is only an embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. The protection scope of the present invention is subject to the protection scope of the claims.
Claims (8)
1. A preparation method of a silicon-carbon composite negative electrode material with a pitaya-like structure is characterized by comprising the following steps:
s1: mixing graphite powder, nano-scale silicon powder or micro-nano-scale silicon powder, a conductive agent and a binder by a dry method;
the graphite powder is any one of artificial graphite, natural graphite and intermediate phase graphite; the conductive agent is any one of acetylene black, carbon fiber, Ketjen black and carbon nano tube; the binder adopts asphalt powder or resin;
step S1 includes the following steps:
s11: mixing graphite powder, nanoscale silicon powder or micro-nanoscale silicon powder, a conductive agent and a binder, and then putting into a high-energy ball milling tank;
s12: keeping an inert environment in a tank body of the high-energy ball milling tank;
s13: continuously ball-milling and mixing the mixture of graphite powder, nano-scale silicon powder or micro-nano-scale silicon powder, the conductive agent and the binder for 8-10h at the rotating speed of 600-900 r/min;
s2: performing wet dispersion processing on the material obtained in the step S1;
s3: drying the material obtained in the step S2;
s4: cold press molding the material obtained in the step S3; wherein, step S4 includes: putting the material obtained in the step S3 into a mould, and pressing for 10-30 minutes in a compression molding or isostatic pressing mode in a pressure environment of 20-50 MPa;
s5: carrying out high-temperature carbonization processing on the material obtained in the step S4, controlling the highest carbonization temperature at 850 ℃ and 950 ℃, and preserving heat for 2-4 h;
s6: crushing and grading the material obtained in the step S5 until the granularity D50 reaches 10-15 um;
s7: coating and granulating the material obtained in the step S6, wherein high-temperature asphalt powder is added into the material obtained in the step S6, and the mixture is stirred and mixed for 2 hours through a mechanical fusion machine;
s8: performing secondary high-temperature carbonization on the material obtained in the step S7, wherein the carbonization process conditions are the same as those in the step S5;
s9: and (5) screening the material obtained in the step (S8) to obtain the silicon-carbon composite anode material with a pitaya-like structure.
2. The preparation method of the silicon-carbon composite anode material with the pitaya-like structure as claimed in claim 1, wherein the step S12 comprises the following steps:
s121: spraying and wetting the high-energy ball milling tank by absolute ethyl alcohol;
s122: vacuumizing the high-energy ball milling tank;
s123: replacing high-purity nitrogen into a high-energy ball milling tank;
s124: jump back to S122 and loop three times.
3. The preparation method of the silicon-carbon composite anode material with the pitaya-like structure as claimed in claim 1, which is characterized by comprising the following steps of: particle size distribution D of graphite powder in step S1505-18um, the nano-scale silicon powderOr the particle size distribution D of the micro-nano silicon powder5050-80nm, and the particle size distribution D of the conductive agent5030-45nm, the particle size distribution D of the binder5020-60 um; the mass percentage of the graphite powder to the silicon-carbon composite negative electrode material with the dragon fruit-like structure is 45-80%, the mass percentage of the nano-scale silicon powder or micro-nano-scale silicon powder to the silicon-carbon composite negative electrode material with the dragon fruit-like structure is 10-40%, the mass percentage of the conductive agent to the silicon-carbon composite negative electrode material with the dragon fruit-like structure is 1-2%, and the mass percentage of the binder to the silicon-carbon composite negative electrode material with the dragon fruit-like structure is 8-14%.
4. The preparation method of the silicon-carbon composite anode material with the pitaya-like structure as claimed in claim 1, which is characterized by comprising the following steps of: step S2 includes the following steps:
s21: adding the material obtained in the step S1 into a solution containing 1% -3% of CMC dispersant to enable the solid content of the solution to reach 45% -60%;
s22: and continuously stirring the solution of the S13 for 8-10h by using a planetary stirrer.
5. The preparation method of the silicon-carbon composite anode material with the pitaya-like structure as claimed in claim 1, which is characterized by comprising the following steps of: step S3 includes: and (5) putting the material obtained in the step S2 into a vacuum drying oven, and performing vacuum drying in a temperature environment of 60-90 ℃ until the solvent is completely evaporated.
6. The preparation method of the silicon-carbon composite anode material with the pitaya-like structure as claimed in claim 1, which is characterized by comprising the following steps of: step S6 includes the steps of:
s61: pre-crushing the material obtained in the step S5 by using a jaw crusher;
s62: and (4) crushing and grading the material obtained in the step (S61) by using a jet mill.
7. The preparation method of the silicon-carbon composite anode material with the pitaya-like structure as claimed in claim 1, which is characterized by comprising the following steps of: the high temperature carbonization processes of steps S5 and S8 are performed using a carbonization furnace.
8. The utility model provides a silicon carbon composite negative electrode material of dragon fruit-like structure which characterized in that: the silicon-carbon composite negative electrode material is prepared by the method for preparing the silicon-carbon composite negative electrode material as defined in any one of claims 1 to 7.
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