CN110635128A - Negative electrode composite material for lithium ion battery and preparation method thereof - Google Patents
Negative electrode composite material for lithium ion battery and preparation method thereof Download PDFInfo
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Abstract
The invention relates to a negative electrode composite material for a lithium ion battery, which consists of a composite graphite substrate, carbon-coated nano-silicon, conductive carbon, an amorphous carbon first coating layer and a macromolecular carbon second coating layer. Firstly, placing nano silicon in a reaction furnace, introducing protective gas, and then introducing cracking gas to perform cracking reaction to obtain carbon-coated nano silicon; adding carbon-coated nano silicon into the composite graphite solution, and preparing a graphite/nano silicon/conductive carbon precursor by drying and granulating; then the surface layer is wrapped with an amorphous carbon first coating layer and a macromolecular carbon second coating layer. The preparation method has the advantages of simple preparation process, high specific capacity of the negative electrode composite material, high first charge-discharge efficiency and excellent cycle stability.
Description
Technical Field
The invention relates to the technical field of lithium ion battery cathode materials, in particular to a cathode composite material for a lithium ion battery.
Background
With the shortage of global petroleum resources and the continuous deterioration of climate environment, the development of clean and energy-saving new energy automobiles is highly valued by countries in the world. The development of new energy automobiles is critical to power sources thereof. At present, a commercial lithium ion battery mainly adopts a graphite negative electrode material, but the theoretical specific capacity of the lithium ion battery is only 372mAh/g, and the requirement of the future lithium ion battery on high energy density cannot be met. Therefore, the development of a novel high-energy-density electrode material is a key point of research, silicon has ultrahigh theoretical specific capacity (4200 mAh/g) and lower lithium removal potential (< 0.5V), the voltage platform of silicon is slightly higher than that of graphite, lithium is difficult to precipitate on the surface during charging, the safety performance is better, and silicon becomes one of the potential choices for the replacement of carbon-based negative electrodes of lithium ion batteries.
However, silicon as a negative electrode material of lithium ion batteries also has disadvantages: (1) the silicon material is easy to generate volume expansion in the charging and discharging processes, so that a conductive network collapses and the electrical cycle performance is influenced; (2) silicon is a semiconductor material, the self conductivity is low, and in the charge-discharge cycle process, the de-intercalation of lithium ions can cause the volume expansion and shrinkage of the material to be more than 300%, so that the structure of the material is damaged and pulverized, the capacity is rapidly attenuated, and the cycle performance is deteriorated. (3) The silicon material is easy to corrode and has capacity attenuation in the circulating process; (4) due to the volume effect of silicon materials, it is difficult to form a stable Solid Electrolyte Interface (SEI) film in an electrolyte, and a new SEI film is continuously formed on the exposed silicon surface along with the destruction of an electrode structure, which aggravates the corrosion and capacity fading of silicon. Analysis shows that the large volume expansion and contraction of the silicon material in the lithium extraction process is the main reason for causing material damage and pulverization, and causing rapid capacity decay. For example, CN103474667A discloses a silicon-carbon negative electrode composite material, which comprises nano-silicon/graphite particles, a first carbon coating layer and an organic cracking layer, wherein the nano-silicon/graphite particles are spherical or spheroidal composite particles formed by coating a nano-silicon particle layer with graphite as a core. CN104617269 discloses a silicon alloy negative electrode composite material, which uses graphite and silicon alloy coated on the surface of the graphite as an inner core, a shell is cracked carbon, and nano-composite, surface modification and coating modification technologies are combined to prepare the silicon alloy negative electrode composite material with a core-shell structure. However, the composite material prepared by the method has high content of metal impurities, is easy to generate self-discharge and has poor high-temperature storage.
CN105070894A discloses a porous silicon-based negative electrode composite material for a lithium ion battery, wherein the negative electrode material is in a capsule structure, a capsule core is made of amorphous porous silicon, a capsule wall is made of a conductive carbon material, the particle size of the amorphous porous silicon is 10-300nm, the pore size of the amorphous porous silicon is 0.5-100nm, and the thickness of the capsule wall is 0.5-10 μm. However, the composite material prepared by the method has more internal pores, lower tap density and low volume energy density.
Therefore, developing a preparation method of the nano silicon-based negative electrode composite material with simple process, excellent performance and environmental friendliness is an important research direction in the field of lithium ion batteries.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a novel high-energy-density negative electrode composite material for a lithium ion battery and a preparation method thereof.
The invention is realized by the following technical scheme:
a negative electrode composite material for a lithium ion battery comprises a composite graphite matrix, carbon-coated nano-silicon uniformly dispersed in pores and on the surface of the composite graphite matrix, conductive carbon uniformly dispersed among the carbon-coated nano-silicon, a first amorphous carbon coating layer and a second polymer carbon coating layer.
The composite graphite substrate is positioned inside the high-energy-density negative electrode composite material for the lithium ion battery, carbon-coated nano silicon is uniformly dispersed in inner pores and the surface of the composite graphite substrate, conductive carbon is uniformly dispersed between the carbon-coated nano silicon, two coating layers are wrapped outside the high-energy-density negative electrode composite material for the lithium ion battery and are respectively an amorphous carbon first coating layer and a polymer carbon second coating layer, and the polymer carbon second coating layer is positioned on the outermost layer.
The composite graphite substrate is one or more of natural crystalline graphite composite particles, natural aphanitic graphite composite particles, natural crystalline vein graphite composite particles, artificial graphite composite particles and conductive graphite composite particles, the nano-silicon material is polycrystalline silicon, monocrystalline silicon and amorphous silicon, preferably monodisperse monocrystalline silicon or polycrystalline silicon particles, and the median diameter of the nano-silicon material is 10 ~ 100 nm.
The conductive carbon is conductive carbon black (zero dimension), carbon nano tube (one dimension) and graphene (two dimensions).
The conductive carbon black is super-p, and d50=1-3 μm; the carbon nano tube is single-walled or multi-walled, the tube diameter is 5-50nm, and the length is 100nm-5 mu m; the graphene is multilayer or single-layer graphene, preferably multilayer graphene, the number of layers is 30-100, and the sheet diameter is 3-10 mu m.
The carbon coating layer of the nano silicon is a gas phase cracking carbon material, preferably one or more of methane, acetylene, natural gas and toluene.
The amorphous carbon first coating layer is a cracked carbon material: the cracking carbon is organic matter cracking carbon, preferably one or more of asphalt, saccharides and high polymer materials, and further preferably one or more of asphalt, phenolic resin, epoxy resin, glucose and sucrose.
The second coating layer of the high molecular carbon is one of polyethylene glycol, polyethers or polyether derivatives
The preparation method of the negative electrode composite material for the lithium ion battery comprises the following steps:
s1, preparing carbon-coated nano silicon: the CVD carbon coating step of the nano silicon comprises the following steps: placing the nano silicon in a CVD furnace, introducing protective gas for heating, introducing cracking gas to start a cracking reaction after the temperature is raised to a reaction temperature, suspending introducing the cracking gas after the reaction is finished, and naturally cooling to obtain amorphous carbon coated nano silicon;
preferably, the protective gas is one or more of nitrogen, helium and argon;
preferably, the cracking gas is one or more of methane, acetylene, natural gas and toluene;
preferably, the mass ratio of the pyrolysis gas to the nano silicon is (1 ~ 4): 50
Preferably, the temperature rise speed is 2 ~ 10 ℃/min;
preferably, the reaction temperature is 600 ~ 1000 ℃ or more;
s2, preparing a graphite/nano-silicon/conductive carbon precursor, namely adding composite graphite into an alcohol solvent, controlling the solid content to be 10 ~ 20%, namely controlling the mass ratio of the composite graphite to the alcohol solvent to be (1 ~ 2): 10, stirring and dispersing to obtain a composite graphite solution, adding the carbon-coated nano-silicon prepared in the step S1 into the composite graphite solution, stirring and dispersing uniformly, adding conductive carbon, stirring and dispersing uniformly, and drying and granulating to obtain the graphite/nano-silicon/conductive carbon precursor;
s3, coating the amorphous carbon first coating layer: and in a protective atmosphere, completely coating the surface of the graphite/nano silicon/conductive carbon precursor prepared in the step S2 by a mechanical solid-phase coating, liquid-phase coating or gas-phase coating method, wherein the coating material is a carbon source substance, and an amorphous carbon first coating layer is formed on the surface of the graphite/nano silicon/conductive carbon precursor to obtain the graphite/nano silicon/conductive carbon/amorphous carbon composite material.
S4, coating a second polymer carbon coating layer: and (4) placing the graphite/nano silicon/conductive carbon/amorphous carbon composite material prepared in the step (S3) into a composite device, adding a high molecular carbon solution for composite granulation, heating and coating, and forming a high molecular carbon second coating layer on the surface of the graphite/nano silicon/conductive carbon/amorphous carbon composite material to obtain the graphite/nano silicon/conductive carbon/amorphous carbon/high molecular carbon composite material, namely the high-energy-density cathode composite material for the lithium ion battery.
Preferably, in step S1, the protective gas is one or more of nitrogen, helium and argon, the pyrolysis gas is one or more of methane, acetylene, natural gas and toluene, and the mass ratio of the pyrolysis gas to the nano-silicon is (1 ~ 4): 50.
Preferably, in step S1, the temperature rise rate is 2 ~ 10 ℃/min, and the reaction temperature is 600 ~ 1000 ℃.
Preferably, in step S2, the alcohol-based solvent is one or more of methanol, ethanol, ethylene glycol, propanol, isopropanol, 1, 2-propanediol, glycerol, n-butanol, 1, 2-butanediol, 1, 3-butanediol, 1, 4-butanediol, n-pentanol, and 2-hexanol.
Preferably, in step S2, the mass ratio of the composite graphite to the carbon-coated nano silicon is (0.3 ~ 2): 1, the mass ratio of the composite graphite to the conductive carbon is (5 ~ 20): 1, and the conductive carbon is conductive carbon black, carbon nanotubes or graphene.
Preferably, in step S2, the drying granulation method is spray drying, flash drying, or freeze drying.
Preferably, in step S3, the carbon source is one or more of hydrocarbons, alkanes, alkenes, phenols, saccharides, organic acids, resins, and polymer materials, preferably one or more of methane, ethylene, asphalt, phenolic resin, epoxy resin, polyvinyl alcohol, polyvinyl chloride, polyethylene glycol, sucrose, glucose, and polyacrylonitrile.
Preferably, in step S3, the coating proportion is 1% ~ 10%, the sintering temperature is 600 ~ 1000 ℃, the thermal reduction time is 10 ~ 240min, the thermal reduction temperature rise rate is 0.5 ~ 15.0.0 ℃/min, the protective atmosphere is one or more of helium, nitrogen and argon, and the equipment adopted for coating is a vacuum furnace, a rotary furnace, a box furnace, a pushed slab kiln or a tubular furnace.
Preferably, in step S4, the polymer carbon solution is one of polyethylene glycol, polyethers or polyether derivatives, and the mass ratio of the polymer carbon solution to the graphite/nano-silicon/conductive carbon/amorphous carbon composite material is 1 (10 ~ 100).
Compared with the prior art, the invention has the following beneficial effects:
(1) the invention provides a nano-silicon cathode composite material of a lithium ion battery, which comprises a composite graphite matrix, carbon-coated nano-silicon, a carbon nano-tube, an amorphous carbon first coating layer and a macromolecular conductive carbon second coating layer. The invention combines the advantages of the existing silicon-carbon material, and the composite graphite is arranged as the matrix, so that the composite graphite can be used as the core of the composite material and can improve the internal conductivity of the composite material. The carbon-coated nano silicon is uniformly adhered to the inner pores and the surface of the graphite, and the carbon coating can effectively inhibit the volume expansion of the nano silicon. The conductive carbon is dispersed in the carbon-coated nano silicon, and can provide a four-way eight-reach conductive network for the composite material. The outer amorphous carbon first coating layer can keep the structure stability of the whole composite material in the charging and discharging process, so that the composite material has a lower specific surface area, the volume expansion and contraction effect of nano silicon in the charging and discharging process is effectively relieved, the electron transmission speed can be improved by the high-molecular conductive carbon second coating layer, the silicon volume expansion is inhibited, and the comprehensive performance of the material is improved. The capacity retention rate of the battery which is assembled by adopting the nano-silicon cathode composite material provided by the invention for testing is more than 80% after the battery is cycled for 1200 weeks, and the first coulombic efficiency is more than 92%.
(2) The nano silicon negative electrode composite material for the lithium ion battery provided by the invention has the advantages of high specific capacity, high first charge-discharge efficiency, excellent cycle stability, simple preparation process, environmental friendliness and no pollution.
Drawings
Fig. 1 is a schematic structural view of a negative electrode composite prepared in example 1.
Fig. 2 is a Scanning Electron Microscope (SEM) image of the nano silicon negative electrode composite prepared in example 1.
Fig. 3 is an XRD pattern of the nano silicon anode composite prepared in example 1.
In the drawings: 1-composite graphite substrate, 2-carbon-coated nano silicon, 3-conductive carbon, 4-amorphous carbon first coating layer and 5-macromolecular carbon second coating layer.
Detailed Description
Example 1
(1) Putting 100nm nano silicon into a CVD furnace, introducing nitrogen for protection, heating at the heating speed of 4 ℃/min to 900 ℃, introducing 3% of methane for starting a cracking reaction, after reacting for 2 hours, suspending introduction of cracking gas, and naturally cooling;
(2) adding a certain amount of composite graphite into an alcohol solvent, controlling the solid content to be 10%, and stirring and dispersing by using a stirrer to obtain a composite graphite solution. Taking amorphous carbon-coated nano-silicon with the mass ratio of 2:1 to composite graphite, placing the amorphous carbon-coated nano-silicon into the composite graphite solution, uniformly dispersing the amorphous carbon-coated nano-silicon in the composite graphite solution by using a stirrer, placing a carbon nano-tube with the mass ratio of 1:0.2 to the composite graphite into the solution, uniformly dispersing the carbon nano-tube, granulating the composite solution in a spray drying mode, and synthesizing to obtain the composite graphite/nano-silicon/carbon nano-tube precursor. Wherein the alcohol solvent is one or more of methanol, ethanol, ethylene glycol, propanol, isopropanol, 1, 2-propylene glycol, glycerol, n-butanol, 1, 2-butylene glycol, 1, 3-butylene glycol, 1, 4-butylene glycol, n-pentanol and 2-hexanol.
(3) And mixing the composite graphite/nano silicon/carbon nanotube precursor with asphalt, wherein the adding proportion of the asphalt is 10%, placing the mixture in a pushed slab kiln, coating the mixture in a solid phase manner, protecting the mixture by using nitrogen, raising the temperature at a speed of 3 ℃/min, keeping the carbonization temperature at 800 ℃, keeping the temperature for 3 hours, and naturally cooling to obtain the composite graphite/nano silicon/carbon nanotube/amorphous carbon.
(4) Placing the composite graphite/nano silicon/carbon nanotube/amorphous carbon composite material into a composite device, adding a polyethylene glycol solution for composite granulation, wherein the adding proportion is 5%, heating and coating to obtain the composite graphite/nano silicon/carbon nanotube/amorphous carbon/high molecular carbon composite material, namely the high-energy-density negative electrode composite material for the lithium ion battery.
A schematic structural diagram of the negative electrode composite material prepared in this embodiment 1 is shown in fig. 1, and the negative electrode composite material is composed of a composite graphite matrix 1, carbon-coated nano silicon 2 uniformly dispersed in pores and on the surface of the composite graphite matrix 1, conductive carbon 3 uniformly dispersed among the carbon-coated nano silicon 2, an amorphous carbon first coating layer 4, and a polymeric carbon second coating layer 5.
The composite graphite substrate 1 is located inside the high-energy-density negative electrode composite material for the lithium ion battery, carbon-coated nano silicon 2 is uniformly dispersed in the inner hole and the surface of the composite graphite substrate 1, conductive carbon 3 is uniformly dispersed between the carbon-coated nano silicon 2, two coating layers, namely an amorphous carbon first coating layer 4 and a high-molecular carbon second coating layer 5, are wrapped outside the high-energy-density negative electrode composite material for the lithium ion battery, and the high-molecular carbon second coating layer 5 is located on the outermost layer.
The scanning electron microscope image of the negative electrode composite material prepared in this example 1 is shown in fig. 2, and the XRD image thereof is shown in fig. 3.
Example 2
(1) Putting a certain amount of 100nm nano silicon into a CVD furnace, introducing nitrogen for protection, heating at the heating speed of 4 ℃/min to 950 ℃, introducing 4% of acetylene to start a cracking reaction, after reacting for 2 hours, suspending introduction of cracking gas, and naturally cooling;
(2) adding a certain amount of composite graphite into an alcohol solvent, controlling the solid content to be 20%, stirring and dispersing by using a stirrer, taking amorphous carbon-coated nano-silicon with the mass ratio of 1:1 to the composite graphite, placing the amorphous carbon-coated nano-silicon into the composite graphite solution, uniformly dispersing by using the stirrer, then placing conductive carbon black with the mass ratio of 1:0.2 to the composite graphite into the solution, uniformly dispersing, granulating the composite solution in a spray drying mode, and synthesizing to obtain the composite graphite/nano-silicon/carbon nanotube precursor. Wherein the alcohol solvent is one or more of methanol, ethanol, ethylene glycol, propanol, isopropanol, 1, 2-propylene glycol, glycerol, n-butanol, 1, 2-butylene glycol, 1, 3-butylene glycol, 1, 4-butylene glycol, n-pentanol and 2-hexanol.
(3) And mixing the composite graphite/nano silicon/carbon nanotube precursor with asphalt, wherein the adding proportion of the asphalt is 5%, placing the mixture in a pushed slab kiln, coating the mixture in a solid phase manner, protecting the mixture by using nitrogen, raising the temperature at a speed of 3 ℃/min, keeping the carbonization temperature at 800 ℃, keeping the temperature for 3 hours, and naturally cooling to obtain the composite graphite/nano silicon/carbon nanotube/amorphous carbon precursor.
(4) And (3) placing the composite graphite/nano silicon/carbon nanotube/amorphous carbon composite material into a composite device, adding a polyethylene glycol solution with the mass ratio of 5% for composite granulation, and heating and coating to obtain the composite graphite/nano silicon/carbon nanotube/amorphous carbon/high-molecular carbon composite material.
Example 3
(1) Putting a certain amount of 100nm nano silicon into a CVD furnace, introducing nitrogen for protection, heating at the heating speed of 4 ℃/min, introducing 5% of natural gas to start a cracking reaction after heating to 1000 ℃, stopping introducing cracking gas after reacting for 2 hours, and naturally cooling;
(2) adding a certain amount of composite graphite into an alcohol solvent, controlling the solid content to be 15%, stirring and dispersing by using a stirrer, taking amorphous carbon-coated nano-silicon with the mass ratio of 1:1 to the composite graphite, placing the amorphous carbon-coated nano-silicon into the composite graphite solution, uniformly dispersing by using the stirrer, then placing graphene with the mass ratio of 1:0.2 to the composite graphite into the solution, uniformly dispersing, granulating the composite solution in a spray drying mode, and synthesizing to obtain the composite graphite/nano-silicon/graphene precursor. Wherein the alcohol solvent is one or more of methanol, ethanol, ethylene glycol, propanol, isopropanol, 1, 2-propylene glycol, glycerol, n-butanol, 1, 2-butylene glycol, 1, 3-butylene glycol, 1, 4-butylene glycol, n-pentanol and 2-hexanol.
(3) The method comprises the steps of carrying out complete surface coating on the composite graphite/nano silicon/graphene precursor by a mechanical solid-phase coating, liquid-phase coating or gas-phase coating method, wherein the coating material is a carbon source substance, and forming an amorphous carbon first coating layer on the surface of the graphite/nano silicon/conductive carbon precursor to obtain the graphite/nano silicon/graphene/amorphous carbon composite material, wherein the carbon source substance is one or more of hydrocarbons, alkanes, alkenes, phenols, sugars, organic acids, resins and high polymer materials, preferably one or more of methane, ethylene, asphalt, phenolic resin, epoxy resin, polyvinyl alcohol, polyvinyl chloride, polyethylene glycol, sucrose, glucose and polyacrylonitrile, the mechanical solid-phase coating, liquid-phase coating or gas-phase coating is carried out at a coating ratio of 1-10%, the sintering temperature is 600 ~ 1000 ℃, the thermal reduction time is 10 36240 min, the thermal reduction heating rate is 0.5 ~.0 ℃/min, and the coating is carried out in a protective atmosphere which is one or more of helium, nitrogen and argon, and the protective atmosphere is one or more of a vacuum furnace, a box furnace, a rotary kiln or a push plate furnace.
(4) Placing the composite graphite/nano silicon/graphene/amorphous carbon composite material in a composite device, adding a polyethylene glycol solution with the mass ratio of 5% for composite granulation, and heating and coating to obtain the composite graphite/nano silicon/graphene/amorphous carbon/high molecular carbon composite material.
Example 4
(1) Putting a certain amount of 100nm nano silicon into a CVD furnace, introducing nitrogen for protection, heating at the heating speed of 4 ℃/min, introducing 5% of toluene to start a cracking reaction after heating to 1000 ℃, stopping introducing cracking gas after reacting for 2 hours, and naturally cooling;
(2) adding a certain amount of composite graphite into an alcohol solvent, controlling the solid content to be 18%, stirring and dispersing by using a stirrer, taking amorphous carbon-coated nano-silicon with the mass ratio of 1:1 to the composite graphite, placing the amorphous carbon-coated nano-silicon into the composite graphite solution, uniformly dispersing by using the stirrer, then placing super-p with the mass ratio of 1:0.2 to the composite graphite into the solution, uniformly dispersing, granulating the composite solution in a spray drying mode, and synthesizing to obtain the composite graphite/nano-silicon/super-p precursor. Wherein the alcohol solvent is one or more of methanol, ethanol, ethylene glycol, propanol, isopropanol, 1, 2-propylene glycol, glycerol, n-butanol, 1, 2-butylene glycol, 1, 3-butylene glycol, 1, 4-butylene glycol, n-pentanol and 2-hexanol.
(3) And mixing the composite graphite/nano silicon/super-p precursor with asphalt, wherein the asphalt adding proportion is 5%, placing the mixture in a pushed slab kiln, carrying out solid phase coating, using nitrogen for protection, carrying out temperature rise at the speed of 3 ℃/min, carrying out carbonization at the temperature of 800 ℃, carrying out heat preservation for 3h, and naturally cooling to obtain the composite graphite/nano silicon/super-p/amorphous carbon precursor.
(4) Placing the composite graphite/nano silicon/super-p/amorphous carbon composite material into a composite device, adding a polyethylene glycol solution with the mass ratio of 5% for composite granulation, and heating and coating to obtain the composite graphite/nano silicon/super-p/amorphous carbon/high molecular carbon composite material.
Comparative example 1
(1) Putting a certain amount of 100nm nano silicon into a CVD furnace, introducing nitrogen for protection, heating at the heating speed of 4 ℃/min, introducing 5% of methane to start a cracking reaction after heating to 1000 ℃, stopping introducing cracking gas after reacting for 2 hours, and naturally cooling;
(2) adding a certain amount of composite graphite into an alcohol solvent, controlling the solid content to be 10 ~ 20%, stirring and dispersing by using a stirrer, taking amorphous carbon-coated nano-silicon with the mass ratio of 1:1 to the composite graphite, placing the amorphous carbon-coated nano-silicon into the composite graphite solution, uniformly dispersing by using the stirrer, granulating the composite solution in a spray drying mode, and synthesizing to obtain the composite graphite/nano-silicon precursor.
(3) And mixing the composite graphite/nano silicon precursor with asphalt, wherein the adding proportion of the asphalt is 5%, placing the mixture in a pushed slab kiln, carrying out solid phase coating, protecting the mixture by using nitrogen, carrying out temperature rise at the speed of 3 ℃/min, carrying out carbonization at the temperature of 800 ℃, carrying out heat preservation for 3h, and naturally cooling to obtain the composite graphite/nano silicon/amorphous carbon precursor.
(4) And (3) placing the composite graphite/nano silicon/amorphous carbon composite material into a composite device, adding a polyethylene glycol solution with the mass ratio of 5% for composite granulation, and heating and coating to obtain the composite graphite/nano silicon/amorphous carbon/high molecular carbon composite material.
Comparative example 2
(1) Putting a certain amount of 100nm nano silicon into a CVD furnace, introducing nitrogen for protection, heating at the heating speed of 4 ℃/min, introducing 5% of methane to start a cracking reaction after heating to 1000 ℃, stopping introducing cracking gas after reacting for 2 hours, and naturally cooling;
(2) adding a certain amount of composite graphite into an alcohol solvent, controlling the solid content to be 10 ~ 20%, stirring and dispersing by using a stirrer, taking amorphous carbon-coated nano-silicon with the mass ratio of 1:1 to the composite graphite, placing the amorphous carbon-coated nano-silicon into the composite graphite solution, uniformly dispersing by using the stirrer, then placing super-p with the mass ratio of 1:0.2 to the composite graphite into the solution, uniformly dispersing, granulating the composite solution in a spray drying manner, and synthesizing to obtain a composite graphite/nano-silicon/super-p precursor.
(3) And mixing the composite graphite/nano silicon/super-p precursor with asphalt, wherein the adding proportion of the asphalt is 5%, placing the mixture in a pushed slab kiln, coating the mixture in a solid phase manner, protecting the mixture by using nitrogen, raising the temperature at a speed of 3 ℃/min, keeping the carbonization temperature at 800 ℃, keeping the temperature for 3 hours, and naturally cooling to obtain the composite graphite/nano silicon/super-p/amorphous carbon composite material.
Performance testing
The preparation of the battery by using the negative electrode materials provided by the embodiment and the comparative example comprises the following specific steps: mixing and dissolving a negative electrode material, a conductive agent and a binder in a solvent according to a mass ratio of 94:2:4, controlling solid content to be 50%, coating the mixture on a copper foil current collector, and drying in vacuum to obtain a negative electrode plate and 1mol/L LiPF6The button cell comprises electrolyte of/EC + DMC + EMC (v/v =1:1:1), SK diaphragm, lithium sheet and shell which are assembled by conventional production process; on the Shenzhen Xinwei Limited battery test system, the test conditions are as follows: at normal temperature, the constant current charge and discharge is carried out at 0.1C, and the charge and discharge cutoff voltage is 0.01V-1.5V. The test results are shown in table 1:
TABLE 1 results of the Performance test of examples and comparative examples
The above description is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiments, and all technical solutions belonging to the idea of the present invention belong to the protection scope of the present invention. It should be noted that various improvements and modifications within the structure and principle of the present invention can be realized by those skilled in the art, and the protection scope of the present invention should be considered.
Claims (10)
1. A negative electrode composite material for a lithium ion battery is characterized in that: the carbon-coated nano silicon composite graphite comprises a composite graphite matrix, carbon-coated nano silicon uniformly dispersed in pores and on the surface of the composite graphite matrix, conductive carbon uniformly dispersed among the carbon-coated nano silicon, an amorphous carbon first coating layer and a macromolecular carbon second coating layer.
2. A preparation method of a negative electrode composite material for a lithium ion battery is characterized by comprising the following steps:
s1, preparing carbon-coated nano silicon: placing the nano silicon in a reaction furnace, introducing protective gas, heating to the reaction temperature, introducing cracking gas, starting cracking reaction, stopping introducing the cracking gas after the reaction is finished, and cooling to obtain carbon-coated nano silicon;
s2, preparing a graphite/nano silicon/conductive carbon precursor: adding the composite graphite into an alcohol solvent, controlling the solid content to be 10-20%, and stirring and dispersing to obtain a composite graphite solution; adding the carbon-coated nano silicon prepared in the step S1 into the composite graphite solution, uniformly stirring and dispersing, then adding conductive carbon, uniformly stirring and dispersing, and drying and granulating to obtain a graphite/nano silicon/conductive carbon precursor;
s3, coating the amorphous carbon first coating layer: and in a protective atmosphere, completely coating the surface of the graphite/nano silicon/conductive carbon precursor prepared in the step S2 by a mechanical solid-phase coating, liquid-phase coating or gas-phase coating method, wherein the coating material is a carbon source substance, and an amorphous carbon first coating layer is formed on the surface of the graphite/nano silicon/conductive carbon precursor to obtain the graphite/nano silicon/conductive carbon/amorphous carbon composite material.
S4, coating a second polymer carbon coating layer: and (4) placing the graphite/nano silicon/conductive carbon/amorphous carbon composite material prepared in the step (S3) into a composite device, adding a high molecular carbon solution for composite granulation, heating and coating, and forming a high molecular carbon second coating layer on the surface of the graphite/nano silicon/conductive carbon/amorphous carbon composite material to obtain the graphite/nano silicon/conductive carbon/amorphous carbon/high molecular carbon composite material, namely the high-energy-density cathode composite material for the lithium ion battery.
3. The method for preparing the negative electrode composite material for the lithium ion battery according to claim 2, wherein the method comprises the following steps: in step S1, the shielding gas is one or more of nitrogen, helium, and argon; the pyrolysis gas is one or more of methane, acetylene, natural gas and toluene, and the mass ratio of the pyrolysis gas to the nano silicon is (1-4): 50.
4. the method for preparing the negative electrode composite material for the lithium ion battery according to claim 2, wherein the method comprises the following steps: in step S1, the temperature rising speed is 2-10 ℃/min; the reaction temperature is 600-1000 ℃.
5. The method for preparing the negative electrode composite material for the lithium ion battery according to claim 2, wherein the method comprises the following steps: in step S2, the alcohol solvent is one or more of methanol, ethanol, ethylene glycol, propanol, isopropanol, 1, 2-propanediol, glycerol, n-butanol, 1, 2-butanediol, 1, 3-butanediol, 1, 4-butanediol, n-pentanol, and 2-hexanol.
6. The method for preparing the negative electrode composite material for the lithium ion battery according to claim 2, wherein the method comprises the following steps: in step S2, the mass ratio of the composite graphite to the carbon-coated nano silicon is (0.3-2): 1, the mass ratio of the composite graphite to the conductive carbon is (5-20): 1; the conductive carbon is one of conductive carbon black, carbon nano tubes and graphene.
7. The method for preparing the negative electrode composite material for the lithium ion battery according to claim 2, wherein the method comprises the following steps: in step S2, the drying granulation method is one of spray drying, flash drying and freeze drying.
8. The method for preparing the negative electrode composite material for the lithium ion battery according to claim 2, wherein the method comprises the following steps: in step S3, the carbon source substance is one or more of hydrocarbons, alkanes, alkenes, phenols, saccharides, organic acids, resins, and polymer materials.
9. The method for preparing the negative electrode composite material for the lithium ion battery according to claim 2, wherein the method comprises the following steps: in the step S3, the coating proportion is 1% -10%, the sintering temperature is 600-1000 ℃, the thermal reduction time is 10-240 min, and the thermal reduction heating rate is 0.5-15.0 ℃/min; the protective atmosphere is one or more of helium, nitrogen and argon; the equipment adopted for coating is a vacuum furnace, a rotary furnace, a box furnace, a pushed slab kiln or a tubular furnace.
10. The method for preparing the negative electrode composite material for the lithium ion battery according to claim 2, wherein the method comprises the following steps: in step S4, the polymer carbon solution is one of polyethylene glycol, polyethers, or polyether derivatives; the mass ratio of the polymer carbon solution to the graphite/nano silicon/conductive carbon/amorphous carbon composite material is 1: (10-100).
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