CN114628653A - Negative plate preparation method, negative plate and lithium ion battery - Google Patents
Negative plate preparation method, negative plate and lithium ion battery Download PDFInfo
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Abstract
The application provides a negative plate preparation method, a negative plate and a lithium ion battery, and belongs to the technical field of lithium ion batteries. The application comprises the following steps: (1) mixing a cationic polymer with silicon dioxide to electrically modify the surface of the silicon dioxide into electropositive property to obtain a modified silicon dioxide template with electropositive property; (2) mixing the silicon dioxide template with a carbon-based material with electronegativity to obtain a mixture, and carrying out a magnesiothermic reduction reaction on the mixture under an inert atmosphere to obtain a porous silicon/carbon composite material; (3) mixing the porous silicon/carbon composite material with asphalt to obtain a carbon-coated structure cathode composite material; (4) and mixing the carbon-coated structure negative electrode composite material, the binder and the conductive agent according to a certain mass ratio to prepare mixed slurry, and coating the mixed slurry on a metal copper foil to obtain the negative electrode plate. Thereby improving the capacity of the lithium ion battery.
Description
Technical Field
The application relates to the field of lithium ion batteries, in particular to a negative plate preparation method, a negative plate and a lithium ion battery.
Background
At present, the negative electrode material of the commercial lithium ion battery is graphite, but the theoretical specific capacity of the graphite is lower (330mAh/g), and the graphite negative electrode is easy to generate 'lithium precipitation', so that potential safety hazards are generated. These fatal defects have failed to satisfy the current demand for high-capacity batteries. The silicon material has the advantages of high specific capacity (4200mA/h), low lithium release and insertion potential, no potential safety hazard caused by lithium precipitation and the like, and becomes a research hotspot of people.
However, silicon undergoes a great volume expansion (up to 400%) during lithium intercalation, resulting in pulverization failure of the material, structural destruction of the electrode, and an unstable solid electrolyte interface (SEI film), thereby drastically decreasing the battery capacity, and decreasing the conductivity and cycle stability, thus limiting its commercial application.
Disclosure of Invention
In order to solve the technical problem of rapid reduction of the battery capacity, the application provides a negative plate preparation method, a negative plate and a lithium ion battery.
In a first aspect, a method for preparing a negative plate is provided, which comprises the following steps:
(1) mixing a cationic polymer with silicon dioxide to electrically modify the surface of the silicon dioxide into electropositive property to obtain a modified silicon dioxide template with electropositive property;
(2) mixing the silicon dioxide template with a carbon-based material with electronegativity to obtain a mixture, and carrying out a magnesiothermic reduction reaction on the mixture under an inert atmosphere to obtain a porous silicon/carbon composite material;
(3) mixing the porous silicon/carbon composite material with asphalt to obtain a carbon-coated structure cathode composite material;
(4) and mixing the carbon-coated structure negative electrode composite material, the binder and the conductive agent according to a certain mass ratio to prepare mixed slurry, and coating the mixed slurry on a metal copper foil to obtain the negative electrode plate.
In one possible embodiment, the preparation process of the silica template in the step (1) is as follows:
mixing a cationic polymer aqueous solution and an anionic monomer aqueous solution in equal volume ratio, performing self-assembly by charge attraction to obtain a copolymer solution with positive charges, centrifuging and cleaning to obtain a copolymer, and adding the copolymer and an initiator into a silicon dioxide alcohol aqueous solution to obtain the silicon dioxide template.
In one possible embodiment, the preparation process of the silica template in the step (1) is as follows:
and adding the cationic polymer solution, the anionic monomer and the initiator into the silicon dioxide alcohol aqueous solution to obtain the silicon dioxide template.
In one possible embodiment, the cationic polymer is one or more of polydimethyldiallylammonium chloride, N-methylene bisacrylamide, hexadecyltrimethylammonium bromide, 2- (methacryloyloxy) ethyltrimethylammonium chloride, and polyethyleneimine;
the inert atmosphere is one or more of argon, nitrogen, hydrogen and helium;
the carbon-based material is one or more of graphite, graphene oxide, carbon nano tubes and carbon nano fibers;
the binder is one or more of sodium carboxymethyl cellulose, polyvinylidene fluoride and styrene butadiene rubber;
the conductive agent is one or more of carbon nano tube, Super-P, carbon black and crystalline flake graphite;
the initiator is one or more of perchloric acid, acrylamide, tetramethylethylenediamine, ammonium persulfate, sodium chloride and sodium hydroxide;
the anionic monomer is one or more of methyl methacrylate, sodium styrene sulfonate and acrylamide.
In one possible embodiment, the method further comprises:
mixing polyoxyethylene powder and acetonitrile solution in a ratio of 1-4:6-15, stirring for 10-18h by using a magnetic stirrer, adding 5% -30% of lithium bis (trifluoromethanesulfonyl) imide, uniformly stirring at a high speed by magnetic force, standing to obtain a first mixed solution, spraying the first mixed solution on the negative electrode sheet, and uniformly covering the negative electrode sheet to form a decorative film.
In one possible embodiment, the preparation process of the mixture in the step (2) is as follows:
dispersing the silicon dioxide template and the carbon-based material with electronegativity in an organic solvent according to the mass ratio of 2:1, stirring, and drying in an oven at 85 ℃ for 10 hours to obtain the mixture; wherein the organic solvent is one or more of deionized water, methanol, ethanol, propanol, butanol, isopropanol and polyvinyl alcohol.
In one possible embodiment, the preparation process of the porous silicon/carbon composite material in the step (2) is as follows:
uniformly grinding the mixture, magnesium and sodium chloride according to the mass ratio of 1: 8-10, placing the mixture in a tubular furnace, heating to 600-800 ℃ at the heating rate of 5 ℃/min under the protection of inert gas, and preserving heat for 2-6 h; adding 1mol/L hydrochloric acid into the prepared sample, etching a byproduct in the magnesium thermal reaction, stirring for 5-12h, cleaning by using 5% -15% hydrogen fluoride to remove unreacted silicon dioxide, cleaning and centrifuging for 3 times, and drying at 80 ℃ for 8-12h to obtain the porous silicon/carbon composite material.
In one possible embodiment, the carbon-coated negative electrode composite material in the step (3) is prepared by the following steps:
adding asphalt into a polyvinyl alcohol solution, and uniformly mixing to obtain a second mixed solution; adding the porous silicon/carbon composite material into the second mixed solution, stirring for 6-16h, completely volatilizing the solvent in an oven, transferring into a rotary kiln, and calcining at a high temperature of 700-1000 ℃ for 3-6h, wherein the protective atmosphere is inert gas during calcining; cooling to room temperature, and then performing jet milling and screening to obtain a composite material; and uniformly mixing the composite material and asphalt for the second time, carbonizing in a rotary kiln again, calcining at 700-1200 ℃ for 2-6h, and performing jet milling and screening again to obtain the carbon-coated structure negative electrode composite material.
In a second aspect, a negative electrode sheet is provided, which is prepared by the preparation method of the first aspect.
In a third aspect, a lithium ion battery is provided, which includes the negative electrode sheet described in the second aspect.
The embodiment of the application has the following beneficial effects:
the carbon-coated structure cathode composite material prepared by the embodiment of the application has a double-layer core framework structure, and the carbon coating of the double carbon layers can provide more lithium ion diffusion channels, promote the transmission between electrons and Li +, ensure good mechanical support and reduce the occurrence of pulverization phenomena to the greatest extent, so that the capacity of a lithium ion battery is improved; and, through pitch cladding carbon casing, can greatly solve and have better structural stability, very big avoiding silicon direct and electrolyte contact, be favorable to forming stable even SEI membrane, reduce reversible capacity loss to the life-span of battery has been promoted.
Of course, not all advantages described above need to be achieved at the same time in the practice of any one product or method of the present application.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the application and, together with the description, serve to explain the principles of the application.
In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly described below, and it is obvious for those skilled in the art to obtain other drawings without inventive exercise.
Fig. 1 is a schematic structural diagram of a carbon-coated negative electrode composite material provided in an embodiment of the present application;
fig. 2 is an adsorption-desorption isotherm diagram of a negative electrode sheet provided in an example of the present application;
fig. 3 is a first charge-discharge curve diagram of the negative electrode sheet provided in the embodiment of the present application.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are some embodiments of the present application, but not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.
The following will describe in detail a method for preparing a negative electrode sheet provided in the examples of the present application with reference to specific embodiments, and the specific steps are as follows:
(1) mixing a cationic polymer with silicon dioxide to electrically modify the surface of the silicon dioxide into electropositive property to obtain a modified silicon dioxide template with electropositive property; wherein, the silicon dioxide is nano-scale silicon powder with the particle size of 5-25 nm;
(2) mixing the silicon dioxide template with a carbon-based material with electronegativity to obtain a mixture, and carrying out a magnesiothermic reduction reaction on the mixture in an inert atmosphere to obtain a porous silicon/carbon composite material (p-Si/C), wherein the magnesiothermic reduction reaction specifically comprises the following steps:
SiO2(s)+2Mg(g)→Si(s)+2MgO(s)
Mg(g)+Si(s)→Mg2Si(s)；
(3) mixing the porous silicon/carbon composite material with asphalt to obtain a carbon-coated structure cathode composite material (p-Si/C @ C), wherein the size of the prepared carbon-coated structure cathode composite material is about 20-30 micrometers;
(4) and mixing the carbon-coated structure negative electrode composite material, the binder and the conductive agent according to a certain mass ratio to prepare mixed slurry, and coating the mixed slurry on a metal copper foil to obtain the negative electrode plate.
Fig. 1 is an SEM image of a p-Si/C @ C negative electrode composite material prepared according to an embodiment of the present application, and it can be seen that the p-Si/C @ C negative electrode composite material is mainly composed of a Si and C double-layer core and an amorphous carbon layer with a shell thickness of 40-100nm, and an outer shell can improve the conductivity of the material, and simultaneously, silicon is prevented from directly contacting with an electrolyte to a certain extent, and the possibility of continuously forming a new Solid Electrolyte Interface (SEI) film in the charging and discharging process is reduced. And the inner carbon layer as a buffer material provides stronger support for the silicon material wrapped by pyrolytic carbon, can greatly relieve the volume effect of the silicon material in the circulating process, and provides guarantee for the silicon to be kept in an original state for a long time, namely, the structural integrity of the electrode is maintained when the volume of the Si is changed.
In a specific embodiment, the preparation process of the silica template in the step (1) is as follows:
mixing a cationic polymer aqueous solution and an anionic monomer aqueous solution in equal volume ratio, performing charge attraction self-assembly to obtain a copolymer solution with positive charges, centrifuging and cleaning to obtain a copolymer, and adding the copolymer and an initiator into a silicon dioxide alcohol aqueous solution to obtain the silicon dioxide template.
In another embodiment, the preparation process of the silica template in the step (1) is as follows:
and adding the cationic polymer solution, the anionic monomer and the initiator into the silicon dioxide alcohol aqueous solution to obtain the silicon dioxide template.
In another embodiment, the cationic polymer is one or more of polydimethyldiallylammonium chloride, N-methylene bisacrylamide, hexadecyltrimethylammonium bromide, 2- (methacryloyloxy) ethyltrimethylammonium chloride, and polyethyleneimine;
the inert atmosphere is one or more of argon, nitrogen, hydrogen and helium;
the carbon-based material is one or more of graphite, graphene oxide, carbon nano tubes and carbon nano fibers;
the binder is one or more of sodium carboxymethyl cellulose, polyvinylidene fluoride and styrene butadiene rubber;
the conductive agent is one or more of carbon nano tube, Super-P, carbon black and crystalline flake graphite;
the initiator is one or more of perchloric acid, acrylamide, tetramethylethylenediamine, ammonium persulfate, sodium chloride and sodium hydroxide;
the anionic monomer is one or more of methyl methacrylate, sodium styrene sulfonate and acrylamide.
In another specific embodiment, the method further comprises:
mixing polyoxyethylene powder and acetonitrile solution in a ratio of 1-4:6-15, stirring for 10-18h by using a magnetic stirrer, adding 5% -30% of lithium bis (trifluoromethanesulfonyl) imide, uniformly stirring at a high speed by magnetic force, standing to obtain a first mixed solution, spraying the first mixed solution on the negative electrode sheet, and uniformly covering the negative electrode sheet to form a decorative film.
The presence of the modified film can form support and protection on the surface of the electrode, and when the volume of the electrode expands, the elastic polymer film can buffer the stress of the electrode, so that the damage to the electrode is reduced.
In another embodiment, the preparation process of the mixture in the step (2) is:
dispersing the silicon dioxide template and the carbon-based material with electronegativity in an organic solvent according to the mass ratio of 2:1, stirring, and drying in an oven at 85 ℃ for 10 hours to obtain the mixture; wherein the organic solvent is one or more of deionized water, methanol, ethanol, propanol, butanol, isopropanol and polyvinyl alcohol.
In another embodiment, the preparation process of the porous silicon/carbon composite material in the step (2) is as follows:
uniformly grinding the mixture, magnesium and sodium chloride according to the mass ratio of 1: 8-10, placing the mixture in a tubular furnace, heating to 600-800 ℃ at the heating rate of 5 ℃/min under the protection of inert gas, and preserving heat for 2-6 h; adding 1mol/L hydrochloric acid into the prepared sample, etching by-products in the magnesium thermal reaction, stirring for 5-12h, cleaning by using hydrogen fluoride with the concentration of 5% -15% to remove unreacted silicon dioxide, cleaning, centrifuging for 3 times, and drying at 80 ℃ for 8-12h to obtain the porous silicon/carbon composite material.
In another specific embodiment, the preparation process of the carbon-coated structure negative electrode composite material in the step (3) is as follows:
adding asphalt into a polyvinyl alcohol solution, and uniformly mixing to obtain a second mixed solution; adding the porous silicon/carbon composite material into the second mixed solution, stirring for 6-16h, completely volatilizing the solvent in an oven, transferring into a rotary kiln, and calcining at a high temperature of 700-1000 ℃ for 3-6h, wherein the protective atmosphere is inert gas during calcining; cooling to room temperature, and then performing jet milling and screening to obtain a composite material; and uniformly mixing the composite material and asphalt for the second time, carbonizing in a rotary kiln again, calcining at 700-1200 ℃ for 2-6h, and performing jet milling and screening again to obtain the carbon-coated structure negative electrode composite material.
In another specific embodiment, the preparation process of the negative electrode sheet in the step (4) is as follows:
weighing the carbon-coated structure negative electrode composite material, the binder and the conductive agent according to the mass ratio of 9: 0.5, uniformly mixing, adding a proper amount of deionized water, grinding and mixing for 3 hours by using a high-speed ball mill to prepare the mixed slurry, uniformly coating the mixed slurry on a metal copper foil with the thickness of 0.012mm, and putting the metal copper foil into a vacuum drying oven to carry out vacuum drying for 12 hours at the temperature of 50 ℃ to obtain the negative electrode plate.
In another specific embodiment, the negative electrode sheet is prepared by the preparation method.
In another specific embodiment, a lithium ion battery is also provided, which includes the foregoing negative electrode sheet.
In the embodiment of the application, firstly, a silicon dioxide template is prepared by using a supramolecular interaction method, a p-Si/C @ C composite material with a double-layer core framework structure is synthesized by virtue of magnesiothermic reduction and carbon coating, and the carbon coating of a double carbon layer can provide more lithium ion diffusion channels, promote the transmission between electrons and Li +, ensure good mechanical support and reduce the occurrence of pulverization phenomenon to the greatest extent, so that the capacity of a lithium ion battery is improved. Second, through pitch cladding carbon casing, can greatly solve and have better structural stability, very big avoid silicon direct and electrolyte contact, be favorable to forming stable even SEI membrane, reduce reversible capacity loss to the life-span of battery has been promoted. And thirdly, an artificial SEI film modification layer is added on the lithium ion battery negative electrode piece, and the artificial SEI film modification layer is constructed on the surface of the electrode, so that the adverse effect caused by the volume change of the silicon-based material during the charge and discharge period can be effectively relieved.
Wherein, the preparation of the silicon dioxide template by using a supramolecular interaction method comprises the following steps: cationic polymers, monomers and initiators are adsorbed on the surface of the silica particles through electrostatic action, so that the polymerization reaction is controlled to be carried out on the surface of the particles. The supermolecule action method does not need to pretreat SiO2 nano-particles, skillfully utilizes the surface active hydroxyl of SiO2 nano-particles and the property of charge attribute of the nano-particles, has mild experimental conditions and simple and easy experimental method, and provides a new method for preparing SiO 2/polymer nano-composite materials. In addition, the dispersity of the Si02 nano particles can be improved through supermolecule actions such as hydrogen bonds and electrostatic interaction, and the aggregation phenomenon under the high-concentration condition is avoided, so that the performance of the composite material is improved, and the aggregation and aggregation phenomenon under the high-concentration condition is avoided.
The present invention is described in further detail below with reference to examples:
the best embodiment is as follows:
1. preparing a porous p-Si/C composite material:
(1) mixing a cationic poly dimethyl diallyl ammonium chloride (PDDA) aqueous solution and an anionic sodium styrene sulfonate (PSS) aqueous solution in an equal volume ratio, performing self-assembly by charge attraction to obtain a PDDA/PSS/PDDA copolymer solution with positive charges, centrifuging, cleaning, adding the copolymer into an SiO2 alcohol aqueous solution, and electrically modifying the surface of SiO2 to be electropositive by using sodium chloride as an initiator.
(2) Mixing a modified SiO2 template with positive electricity and graphene oxide with negative electricity according to the mass ratio of 2:1, dispersing, stirring in a mixed solvent of deionized water and ethanol for 6 hours, drying in an oven at 85 ℃ for 10 hours, uniformly grinding the obtained SiO 2/graphene oxide, Mg and NaCl in a mass ratio of 1: 8, placing in a tubular furnace, heating to 650 ℃ at a heating rate of 5 ℃/min under the protection of inert gas, and preserving heat for 3 hours; adding 1mol hydrochloric acid into the prepared sample, stirring for 12h, etching by-products in the magnesium thermal reaction, adding 10% HF, stirring for 1h to remove unreacted SiO2, cleaning, centrifuging for 3 times, and drying at 80 ℃ for 12h to obtain the pure p-Si/C composite material.
Preparing a p-Si/C @ C negative electrode composite material:
adding asphalt into a PVA solution, uniformly mixing, adding a p-Si/C composite material into the mixed solution, stirring for 10 hours, completely volatilizing a solvent in an oven, transferring the solvent into a rotary kiln, calcining for 4 hours at the high temperature of 850 ℃, taking argon as a protective atmosphere during calcination, cooling to room temperature, performing jet milling and screening, uniformly mixing the obtained composite material with asphalt for the second time, carbonizing the composite material in the rotary kiln, calcining for 3 hours at the high temperature of 900 ℃, performing jet milling and screening again to obtain the p-Si/C @ C cathode composite material with the carbon coating structure, wherein the particle size of the finished product is 23-25 mu m, and the particle size of the composite material is good in particle size consistency and good in coating effect.
3. Preparing a negative plate:
weighing the carbon-coated structure negative electrode composite material, the binder and the conductive agent according to the mass ratio of 9: 0.5, uniformly mixing, adding a proper amount of deionized water, grinding and mixing for 3 hours by using a high-speed ball mill to prepare the mixed slurry, uniformly coating the mixed slurry on a metal copper foil with the thickness of 0.012mm, and putting the metal copper foil into a vacuum drying oven to carry out vacuum drying for 12 hours at the temperature of 50 ℃ to obtain the negative electrode plate. Finally assembled into button cells for testing.
The first embodiment is as follows:
1. preparing a porous p-Si/C composite material:
(1) adding a cationic polymer N, N-methylene bisacrylamide polymer solution, an acrylamide monomer and ammonium persulfate serving as an initiator into a SiO2 alcohol water solution to electrically modify the surface of SiO2 into positive electricity.
(2) The mass ratio of the positively charged modified SiO2 template to the negatively charged graphene oxide is 2: dispersing 1, dispersing in an organic solvent, stirring for 6h, drying in an oven at 85 ℃ for 10h, uniformly grinding the obtained SiO 2/carbon-based material, Mg and NaCl in a mass ratio of 1: 8, placing in a tubular furnace, heating to 650 ℃ at a heating rate of 5 ℃/min under the protection of inert gas, and preserving heat for 3 h; adding 1mol/L hydrochloric acid into the prepared sample, etching by-products in the magnesium thermal reaction, stirring for 12h, cleaning by 5% HF to remove unreacted SiO2, centrifugally separating precipitates, washing 3 times by deionized water and absolute ethyl alcohol respectively, drying for 12h at 80 ℃, and collecting to obtain the pure p-Si/C composite material.
Preparing a p-Si/C @ C negative electrode composite material:
adding asphalt into a PVA solution, uniformly mixing, adding a p-Si/C composite material into the mixed solution, stirring for 12h, completely volatilizing a solvent in an oven, transferring the solvent into a rotary kiln, calcining for 4h at 800 ℃ at high temperature under the condition that argon is used as protective atmosphere during calcination, cooling to room temperature, performing jet milling and screening, uniformly mixing the obtained composite material with the asphalt for the second time, carbonizing in the rotary kiln again, calcining for 2h at 1000 ℃ at high temperature, and performing jet milling and screening again to obtain the p-Si/C @ C cathode composite material with the carbon coating structure, wherein the particle size consistency is good, and the coating effect is good.
3. Preparing a negative plate:
weighing the carbon-coated structure negative electrode composite material, the binder and the conductive agent according to the mass ratio of 9: 0.5, uniformly mixing, adding a proper amount of deionized water, grinding and mixing for 3 hours by using a high-speed ball mill to prepare the mixed slurry, uniformly coating the mixed slurry on a metal copper foil with the thickness of 0.012mm, and putting the metal copper foil into a vacuum drying oven to carry out vacuum drying for 12 hours at the temperature of 50 ℃ to obtain the negative electrode plate. Finally assembled into button cells for testing.
Example two:
1. preparing a porous p-Si/C composite material:
(1) mixing a cationic poly dimethyl diallyl ammonium chloride (PDDA) aqueous solution and an anionic sodium styrene sulfonate (PSS) aqueous solution in an equal volume ratio, performing self-assembly by charge attraction to obtain a PDDA/PSS/PDDA copolymer solution with positive charges, centrifuging, cleaning, adding the copolymer into an SiO2 alcohol aqueous solution, and electrically modifying the surface of SiO2 to be electropositive by using sodium chloride as an initiator.
(2) Mixing a modified SiO2 template with positive electricity and graphene oxide with negative electricity according to the mass ratio of 2: dispersing 1, dispersing in an organic solvent, stirring for 5h, drying in an oven at 85 ℃ for 10h, uniformly grinding the obtained SiO 2/carbon-based material, Mg and NaCl in a mass ratio of 1: 9, placing in a tubular furnace, heating to 600 ℃ at a heating rate of 5 ℃/min under the protection of inert gas, and preserving heat for 3 h; adding 1mol/L hydrochloric acid into the prepared sample, etching by-products in the magnesium thermal reaction, stirring for 12h, cleaning by using 10% HF (hydrogen fluoride) to remove unreacted SiO2, washing the precipitate by using deionized water and absolute ethyl alcohol respectively for 3 times after centrifugal separation, drying for 12h at the temperature of 80 ℃, and collecting to obtain the pure p-Si/C composite material.
Preparing a p-Si/C @ C negative electrode composite material:
adding asphalt into a PVA solution, uniformly mixing, adding a p-Si/C composite material into the mixed solution, stirring for 12h, completely volatilizing a solvent in an oven, transferring the solvent into a rotary kiln, calcining for 4h at 800 ℃ at high temperature under the condition that argon is used as protective atmosphere during calcination, cooling to room temperature, performing jet milling and screening, uniformly mixing the obtained composite material with the asphalt for the second time, carbonizing in the rotary kiln again, calcining for 2h at 1050 ℃ at high temperature, and performing jet milling and screening again to obtain the p-Si/C @ C cathode composite material with the carbon coating structure, wherein the particle size consistency is good, and the coating effect is good.
3. Preparing a negative plate:
weighing the carbon-coated structure negative electrode composite material, the binder and the conductive agent according to the mass ratio of 9: 0.5, uniformly mixing, adding a proper amount of deionized water, grinding and mixing for 3 hours by using a high-speed ball mill to prepare the mixed slurry, uniformly coating the mixed slurry on a metal copper foil with the thickness of 0.012mm, and putting the metal copper foil into a vacuum drying oven to carry out vacuum drying for 12 hours at the temperature of 50 ℃ to obtain the negative electrode plate. Finally assembling the button cell for testing.
Example three:
1. preparing a porous p-Si/C composite material:
(1) adding a cationic polymer N, N-methylene bisacrylamide polymer solution, an acrylamide monomer and ammonium persulfate serving as an initiator into a SiO2 alcohol water solution to electrically modify the surface of SiO2 into positive electricity.
(2) Mixing a modified SiO2 template with positive electricity and graphene oxide with negative electricity according to the mass ratio of 2: dispersing 1, dispersing in an organic solvent, stirring for 5h, drying in an oven at 85 ℃ for 10h, uniformly grinding the obtained SiO 2/carbon-based material, Mg and NaCl in a mass ratio of 1: 9, placing in a tubular furnace, heating to 600 ℃ at a heating rate of 5 ℃/min under the protection of inert gas, and preserving heat for 3 h; adding 1mol/L hydrochloric acid into the prepared sample, etching by-products in the magnesium thermal reaction, stirring for 12h, cleaning by 15% HF to remove unreacted SiO2, centrifugally separating precipitates, washing 3 times by deionized water and absolute ethyl alcohol respectively, drying for 12h at 80 ℃, and collecting to obtain the pure p-Si/C composite material.
Preparing a p-Si/C @ C negative electrode composite material:
adding asphalt into a PVA solution, uniformly mixing, adding a p-Si/C composite material into the mixed solution, stirring for 12h, completely volatilizing a solvent in an oven, transferring the solvent into a rotary kiln, calcining for 4h at 850 ℃ and high temperature under the protection atmosphere of argon during calcination, cooling to room temperature, performing jet milling and screening, uniformly mixing the obtained composite material with the asphalt for the second time, carbonizing in the rotary kiln again, calcining for 2h at 950 ℃ and performing jet milling and screening again to obtain the p-Si/C @ C cathode composite material with the carbon coating structure, wherein the particle size consistency is good, and the coating effect is good.
3. Preparing a negative plate:
weighing the carbon-coated structure negative electrode composite material, the binder and the conductive agent according to the mass ratio of 9: 0.5, uniformly mixing, adding a proper amount of deionized water, grinding and mixing for 3 hours by using a high-speed ball mill to prepare the mixed slurry, uniformly coating the mixed slurry on a metal copper foil with the thickness of 0.012mm, and putting the metal copper foil into a vacuum drying oven to carry out vacuum drying for 12 hours at the temperature of 50 ℃ to obtain the negative electrode plate. Finally assembling the button cell for testing.
The negative electrode sheets obtained in the above-described preferred examples and examples 1 to 3 were assembled into a battery in the following manner and tested according to the following discharge test conditions, thereby obtaining the test data of tables 1 and 2 and the graphs of fig. 2 and 3.
Assembling the battery: punching the negative pole piece into a circular piece with the diameter of 16mm, and then performing tabletting by using a tabletting machine at 20MPa to obtain an electrode piece; and finally, assembling the battery in a glove box filled with argon in an oxygen-free environment to form a button cell. Dissolving in a solvent of 1: 1: 1mol/LLI PF6 of EC/DMC/EMC of 1 is used as electrolyte, a lithium sheet is used as a counter electrode, and a polypropylene porous membrane with the thickness of 19mm is selected as a diaphragm. And aging the assembled button cell for 24 hours, and testing the electrochemical performance by using a cell testing system at 25 ℃.
And (4) under the condition of electricity deduction test: (1) constant current discharging: 0.01C, cutoff voltage 0.005V; (2) standing: 10 min; (3) and (3) constant current charging condition: 0.01C, cut-off voltage 2.0V is terminated; (4) standing: 10 min; (5) and (3) circulation: 50 times.
Table 1:
the adsorption isotherm type of the material belongs to a fourth class of adsorption isotherms, the characteristics of the porous material are verified, and as can be seen from table 1 and fig. 2, the N2 adsorption amount of P-Si/C @ C is suddenly increased within the range of P/P0 of 0.8-1.0, and a remarkable hysteresis loop exists, which indicates that a large number of narrow micropores exist in the material, the micropores are about 1.4nm in pore diameter width, and are mainly caused by gases such as H2O and CO2 released by pyrolysis in the carbonization process. The abundant microporous structure in the carbon layer is beneficial to the migration of lithium ions in the charging and discharging processes, and the ion transmission rate is effectively increased. The large specific surface area and the uniformly distributed channels shorten the diffusion path of lithium ions, increase the reactivity of the composite material and enhance the electrical property of the composite material.
Wherein, compare in large granule silicon, small-size nanometer silicon has effectively shortened the diffusion path that potassium ion embedding/deviate from the process to have bigger porosity, can buffer the stress variation in the charge-discharge process to a certain extent, secondly, the even complex of outer coating can further provide bigger buffer space for the volume expansion of nanometer silicon, effectively prevent the reunion of nanometer silicon, electrode structure breakage and SEI membrane from repeatedly forming, thereby make whole electrode structure and SEI membrane have good stability.
Table 2:
as can be seen by combining the table 2 and the figure 3, the first charge and discharge specific capacities of the p-Si/C @ C composite material are 1305mAh/g and 1112mAh/g respectively, and the first coulombic efficiency is 85.21%, which indicates that the material has high reversible capacity, and the special structure of the p-Si/C @ C composite material is helpful for ensuring that silicon is separated from a current collector and crushed due to the volume effect in the lithium intercalation and deintercalation process, but still has certain conductivity, so that the situation that Li + cannot be deintercalated is effectively prevented, and the irreversible capacity is low. Moreover, the discharge curves of the 50 th cycle tend to be consistent, which shows that the composite structure forms a stable SEI film in the first cycle process, avoids the situation that a new SEI film is continuously formed in the later period, and simultaneously shows that the double protection of the pyrolytic carbon and the p-Si/C matrix and the formed buffer space are successfully adapted to the internal stress generated by the volume effect. The p-Si/C and the pitch pyrolytic carbon are synergistic, so that the high electronic conduction rate and the high lithium ion diffusion rate of the electrode are ensured, and the composite material shows high first coulombic efficiency, high specific capacity and excellent cycle performance. The porous structure buffers the volume expansion of the material in the lithium intercalation process, and the cycle performance of the material is further improved.
It is noted that, in this document, relational terms such as "first" and "second," and the like, may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.
The above description is merely exemplary of the present application and is presented to enable those skilled in the art to understand and practice the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the application. Thus, the present application is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (10)
1. The preparation method of the negative plate is characterized by comprising the following steps of:
(1) mixing a cationic polymer with silicon dioxide to electrically modify the surface of the silicon dioxide into electropositive property to obtain a modified silicon dioxide template with electropositive property;
(2) mixing the silicon dioxide template with a carbon-based material with electronegativity to obtain a mixture, and carrying out a magnesiothermic reduction reaction on the mixture under an inert atmosphere to obtain a porous silicon/carbon composite material;
(3) mixing the porous silicon/carbon composite material with asphalt to obtain a carbon-coated structure cathode composite material;
(4) and mixing the carbon-coated structure negative electrode composite material, the binder and the conductive agent according to a certain mass ratio to prepare mixed slurry, and coating the mixed slurry on a metal copper foil to obtain the negative electrode plate.
2. The method according to claim 1, wherein the silica template in the step (1) is prepared by:
mixing a cationic polymer aqueous solution and an anionic monomer aqueous solution in equal volume ratio, performing charge attraction self-assembly to obtain a copolymer solution with positive charges, centrifuging and cleaning to obtain a copolymer, and adding the copolymer and an initiator into a silicon dioxide alcohol aqueous solution to obtain the silicon dioxide template.
3. The method according to claim 1, wherein the silica template in the step (1) is prepared by:
and adding the cationic polymer solution, the anionic monomer and the initiator into the silicon dioxide alcohol aqueous solution to obtain the silicon dioxide template.
4. The method of claim 2 or 3,
the cationic polymer is one or more of poly dimethyl diallyl ammonium chloride, N-methylene bisacrylamide, hexadecyl trimethyl ammonium bromide, 2- (methacryloyloxy) ethyl trimethyl ammonium chloride and polyethyleneimine;
the inert atmosphere is one or more of argon, nitrogen, hydrogen and helium;
the carbon-based material is one or more of graphite, graphene oxide, carbon nano tubes and carbon nano fibers;
the binder is one or more of sodium carboxymethyl cellulose, polyvinylidene fluoride and styrene butadiene rubber;
the conductive agent is one or more of carbon nano tube, Super-P, carbon black and crystalline flake graphite;
the initiator is one or more of perchloric acid, acrylamide, tetramethylethylenediamine, ammonium persulfate, sodium chloride and sodium hydroxide;
the anionic monomer is one or more of methyl methacrylate, sodium styrene sulfonate and acrylamide.
5. The method of claim 1, further comprising:
mixing polyoxyethylene powder and acetonitrile solution in a ratio of 1-4:6-15, stirring for 10-18h by using a magnetic stirrer, adding 5% -30% of lithium bis (trifluoromethanesulfonyl) imide, uniformly stirring at a high speed by magnetic force, standing to obtain a first mixed solution, spraying the first mixed solution on the negative electrode sheet, and uniformly covering the negative electrode sheet to form a decorative film.
6. The method according to claim 1, wherein the mixture in the step (2) is prepared by:
dispersing the silicon dioxide template and the carbon-based material with electronegativity in an organic solvent according to the mass ratio of 2:1, stirring, and drying in an oven at 85 ℃ for 10 hours to obtain the mixture; wherein the organic solvent is one or more of deionized water, methanol, ethanol, propanol, butanol, isopropanol and polyvinyl alcohol.
7. The method according to claim 1, wherein the porous silicon/carbon composite material in the step (2) is prepared by:
uniformly grinding the mixture, magnesium and sodium chloride according to the mass ratio of 1: 8-10, placing the mixture in a tubular furnace, heating to 600-800 ℃ at the heating rate of 5 ℃/min under the protection of inert gas, and preserving heat for 2-6 h; adding 1mol/L hydrochloric acid into the prepared sample, etching a byproduct in the magnesium thermal reaction, stirring for 5-12h, cleaning by using 5% -15% hydrogen fluoride to remove unreacted silicon dioxide, cleaning and centrifuging for 3 times, and drying at 80 ℃ for 8-12h to obtain the porous silicon/carbon composite material.
8. The method according to claim 1, wherein the carbon-coated structure negative electrode composite material in the step (3) is prepared by:
adding asphalt into the polyvinyl alcohol solution, and uniformly mixing to obtain a second mixed solution; adding the porous silicon/carbon composite material into the second mixed solution, stirring for 6-16h, completely volatilizing the solvent in an oven, transferring into a rotary kiln, and calcining at the high temperature of 700-1000 ℃ for 3-6h, wherein the protective atmosphere is inert gas during calcining; cooling to room temperature, and then performing jet milling and screening to obtain a composite material; and uniformly mixing the composite material and asphalt for the second time, carbonizing in a rotary kiln again, calcining at 700-1200 ℃ for 2-6h, and performing jet milling and screening again to obtain the carbon-coated structure negative electrode composite material.
9. A negative electrode sheet, characterized by being produced by the production method according to any one of claims 1 to 8.
10. A lithium ion battery comprising the negative electrode sheet according to claim 9.
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| CN116936775A (en) * | 2023-09-15 | 2023-10-24 | 宁德时代新能源科技股份有限公司 | Negative electrode material, preparation method thereof, negative electrode plate, battery and power utilization device |
| CN116969464A (en) * | 2023-09-22 | 2023-10-31 | 中石油深圳新能源研究院有限公司 | Lithium ion battery negative electrode material and preparation method thereof |
| CN118099402A (en) * | 2024-04-28 | 2024-05-28 | 青岛泰达天润碳材料有限公司 | Spherical graphite/silicon anode material and preparation method and application thereof |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN116936775A (en) * | 2023-09-15 | 2023-10-24 | 宁德时代新能源科技股份有限公司 | Negative electrode material, preparation method thereof, negative electrode plate, battery and power utilization device |
| CN116969464A (en) * | 2023-09-22 | 2023-10-31 | 中石油深圳新能源研究院有限公司 | Lithium ion battery negative electrode material and preparation method thereof |
| CN118099402A (en) * | 2024-04-28 | 2024-05-28 | 青岛泰达天润碳材料有限公司 | Spherical graphite/silicon anode material and preparation method and application thereof |
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