CN115602837A - Negative electrode material and preparation method thereof, negative electrode coating, negative electrode plate and lithium ion battery - Google Patents
Negative electrode material and preparation method thereof, negative electrode coating, negative electrode plate and lithium ion battery Download PDFInfo
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Abstract
The invention provides a negative electrode material and a preparation method thereof, a negative electrode coating, a negative electrode plate and a lithium ion battery, wherein the negative electrode material comprises modified graphite particles and hard carbon dispersed among the modified graphite particles, and the particle size of the modified graphite particles is larger than that of the hard carbon; wherein the modified graphite particles comprise: the graphite core layer and the amorphous carbon shell layer are coated on the outer surface of the graphite core layer; and the carbon nanotube layer is coated on the outer surface of the amorphous carbon shell layer far away from the graphite core layer. When the cathode material is applied to a lithium ion battery, the battery shows excellent quick charge performance, low temperature performance, higher energy density and excellent cycle performance.
Description
Technical Field
The invention relates to the field of lithium ion batteries, and particularly relates to a negative electrode material and a preparation method thereof, a negative electrode coating, a negative electrode plate and a lithium ion battery.
Background
At present, the negative electrode material of the lithium ion battery in the market is usually a graphite material, and the supply chain is very mature. For example, in the prior art, patent CN105449182B discloses a negative electrode active material for a lithium ion battery, a preparation method thereof, a lithium ion negative electrode material, a lithium ion negative electrode, and a lithium ion battery. Specifically, the negative active material is in a core-shell structure, and the core of the negative active material is at least one of natural spherical graphite, soft carbon and hard carbon. The shell contains amorphous carbon, tin-cobalt alloy and carbon nano tube soft carbon, wherein the content of the carbon nano tube is 0.5-2%, the three can be mixed, and the content range of the coated carbon nano tube is not crossed. However, the content of the carbon nanotubes is low, which is not favorable for point and linear contact between graphite and graphite particles and between graphite and hard carbon particles, so that a smooth electron-conductive three-dimensional network is not easy to construct, and the rate capability, the quick charge performance and the low temperature performance of the mixed cathode active material are poor.
Patent CN103633288A discloses a composite negative electrode material for a lithium ion battery, a preparation method thereof, a negative electrode plate of the lithium ion battery and the lithium ion battery. Specifically, the negative active material is of a core-shell structure, but a coating layer of the negative active material is a lithium insertion transition metal oxide to cover active sites of graphite itself, so that irreversible capacity of the lithium ion battery in initial charging is reduced. However, the raw materials of the graphite particle coating layer are not easy to obtain, the cost is high, the treatment is complex and tedious, and meanwhile, the fast charging performance and the low-temperature performance of the composite negative electrode material are poor.
Patent CN105993088B discloses a coated negative electrode active material for a lithium ion battery, a slurry for a lithium ion battery, a negative electrode for a lithium ion battery, and a method for producing a coated negative electrode active material for a lithium ion battery. Specifically, the coating layer of the negative active material is resin and a conductive auxiliary agent, which mainly function to reduce the irreversible capacity of the lithium ion battery, but the rate performance of the negative active material is poor.
In summary, the lithium ion battery prepared by the prior art has the problems of poor quick charge performance, poor low temperature performance, low energy density, poor cycle performance and the like. Therefore, it is highly desirable to prepare a lithium ion battery to improve the above problems.
Disclosure of Invention
The invention mainly aims to provide a negative electrode material and a preparation method thereof, a negative electrode coating, a negative electrode plate and a lithium ion battery, and aims to solve the problems that the lithium ion battery prepared by the prior art is poor in quick charge performance, low temperature performance, energy density and cycle performance and the like.
In order to achieve the above object, according to one aspect of the present invention, there is provided an anode material comprising modified graphite particles and hard carbon dispersed between the modified graphite particles, the particle diameter of the modified graphite particles being larger than that of the hard carbon; wherein the modified graphite particles comprise: a graphite core layer; an amorphous carbon shell layer coated on the outer surface of the graphite core layer; and the carbon nanotube layer is coated on the outer surface of the amorphous carbon shell layer far away from the graphite core layer.
Further, the thickness of the amorphous carbon shell layer of the modified graphite particles is 50-150 nm; preferably, the thickness of the carbon nanotube layer is 20-80 nm; the Dv50 particle diameter of the graphite core layer is preferably 10 to 20 μm; the Dv50 particle diameter of the modified graphite particle is preferably 10.0 to 20.5. Mu.m, more preferably 10 to 16 μm.
Further, the weight content of the hard carbon is 1-10 wt%; the modified graphite particles preferably have a weight content of 90 to 99 wt.%.
Further, the graphitization degree of the modified graphite particles is more than or equal to 92 percent, and preferably 93-95 percent; the gram capacity of the modified graphite particles is preferably more than or equal to 350mAh/g, and more preferably 355-360 mAh/g.
Further, the Dv50 particle diameter of the hard carbon is 3 to 6 μm; preferably, the gram capacity of the hard carbon is more than or equal to 380mAh/g, and more preferably 395-420 mAh/g; the negative electrode material preferably has a defect degree of 0.30 to 0.60, more preferably 0.40 to 0.55.
In order to achieve the above object, according to another aspect of the present invention, there is provided a method of preparing an anode material, the method comprising: providing a graphite core layer; coating an amorphous carbon shell layer on the outer surface of the graphite core layer; coating a carbon nanotube layer on the outer surface of the amorphous carbon shell layer far away from the graphite core layer to obtain modified graphite particles; and mixing the modified graphite particles with hard carbon to obtain the cathode material.
Further, the preparation method of the anode material comprises the following steps: step S1: crushing graphite, and then carrying out first sintering to obtain a graphite core layer; step S2: mixing the graphite core layer and the carbon coating agent, and performing second sintering to coat the amorphous carbon shell layer on the outer surface of the graphite core layer to obtain graphite particles coated with the amorphous carbon shell layer; and step S3: mixing the graphite particles coated with the amorphous carbon shell layer and the carbon nano tube coating agent, and performing third sintering to coat the carbon nano tube layer on the outer surface of the amorphous carbon shell layer, which is far away from the graphite core layer, so as to obtain modified graphite particles; and step S4: and mixing the modified graphite particles with hard carbon to obtain the cathode material.
Further, the first sintering in step S1 is performed in a graphitization furnace, and the first sintering temperature is equal to or higher than 2400 ℃, preferably 2400 to 3000 ℃.
Further, the carbon coating agent in the step S2 is selected from asphalt with the softening point temperature of 250-280 ℃; preferably, the using amount of the carbon coating agent is 3-8 wt% of the weight of the graphite core layer; the sintering temperature of the second sintering is preferably 600-800 ℃, and the second sintering time is 2-6 h.
Further, the carbon nanotube coating agent in step S3 includes a carbon-containing binder and carbon nanotubes; preferably the carbonaceous binder is selected from the group consisting of bitumen having a softening point temperature of 180 to 230 ℃; preferably, the carbon nano tube is selected from multi-wall carbon nano tube and/or single-wall carbon nano tube, the length-diameter ratio of the carbon nano tube is (50-100) 1; the sintering temperature of the third sintering is preferably 600-800 ℃, and the third sintering time is 2-6 h; preferably, the amount of the carbon nanotube coating agent is 3 to 8wt% of the weight of the graphite particles coated with the amorphous carbon shell layer; in the carbon nanotube coating agent, the weight ratio of the carbon-containing binder to the carbon nanotubes is preferably (1-1.5): 1.
Further, the weight ratio of the modified graphite particles to the hard carbon in the step S4 is (99-90) to (1-10); preferably, mixing the modified graphite particles with hard carbon in a mechanical running-in mode; the rotation speed in mechanical running-in is preferably 50 to 150rpm.
According to another aspect of the present invention, there is provided an anode coating, which includes an anode material, a binder and a dispersant, wherein the anode material is the anode material or the anode material prepared by the method for preparing the anode material.
According to another aspect of the invention, a negative electrode plate is provided, which comprises a coating and a substrate, wherein the coating is obtained by coating and molding the negative electrode coating.
According to another aspect of the invention, a lithium ion battery is provided, and the lithium ion battery comprises the above negative electrode plate.
When the cathode material prepared by the invention is applied to a lithium ion battery, the battery shows excellent quick charge performance, low temperature performance, higher energy density and excellent cycle performance.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this application, are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification, illustrate embodiment(s) of the invention and together with the description serve to explain the invention and not to limit the invention. In the drawings:
fig. 1 shows a schematic structural view of an anode material in one embodiment of the invention;
fig. 2 shows a partially enlarged view of the modified graphite structure in the negative electrode material structure of fig. 1.
Wherein the figures include the following reference numerals:
1: modifying the graphite particles; 2: hard carbon;
11: a graphite core layer; 12: an amorphous carbon shell layer; 13: a carbon nanotube layer.
Detailed Description
It should be noted that, in the present application, the embodiments and features of the embodiments may be combined with each other without conflict. The present invention will be described in detail below with reference to the accompanying drawings in conjunction with embodiments.
The defect degree is as follows: the defect degree related to the application is related parameters in a Raman test, and specifically, the spectrum of a Raman spectrum of a negative electrode material to be tested is 1250cm -1 To 1650cm -1 Peak intensity Id of (A) and hard carbon at a spectrum of 1500cm -1 To 1650cm -1 The ratio of the peak intensities Ig of (a) is the defect degree mentioned in this application.
As described in the background of the invention section, the lithium ion batteries prepared by the prior art have the problems of poor quick charge performance, poor low temperature performance, low energy density, poor cycle performance and the like. In order to solve this problem, the present invention provides an anode material, as shown in fig. 1, comprising modified graphite particles 1 having a particle diameter larger than that of hard carbon and hard carbon 2 dispersed between the modified graphite particles. As shown in fig. 2, the modified graphite particles include a graphite core layer 11, an amorphous carbon shell layer 12 coated on an outer surface of the graphite core layer, and a carbon nanotube layer 13 coated on an outer surface of the amorphous carbon shell layer away from the graphite core layer.
Firstly, the graphite is taken as a nuclear layer, and the outer surface of the graphite nuclear layer is coated with an amorphous carbon shell layer, the amorphous carbon shell layer can obviously increase the surface defect degree of modified graphite particles, so that the surfaces of the modified graphite particles are promoted to have active sites, and the active sites can enable lithium ions to be more conveniently extracted and inserted in the charging and discharging process of the battery, and especially when the battery is charged at a large multiplying power (more lithium ions are extracted from a positive electrode), the active sites can form a large number of vacancies to store the lithium ions, so that the buffering effect is achieved, and the quick charging performance of the battery is further better (namely, when the battery is charged at a short time and a large multiplying power, the battery can keep better electrochemical performance). Secondly, the carbon nanotube layer is further coated on the outer surface of the amorphous carbon shell layer, the carbon nanotube has good conductivity, and the point and line contact among modified graphite particles and between the modified graphite and hard carbon can be increased, so that an electronic conductive three-dimensional network can be constructed and formed, the overall conductivity of the negative electrode material is improved, the migration impedance is reduced, and the rate capability, the quick charge performance and the low temperature performance of the battery are improved. Thirdly, the modified graphite particles and hard carbon are further compounded to form the negative electrode material, the hard carbon has the characteristics of high multiplying power, good cycle and low expansion, and the hard carbon is mixed in the modified graphite to prepare the negative electrode material, so that the multiplying power performance, the quick charge performance and the low temperature performance of the lithium ion battery can be greatly improved, and the cycle performance of the battery is also obviously improved. And moreover, the hard carbon is dispersedly arranged in gaps of the modified graphite particles to be filled, so that the close packing among the particles can be ensured, the compacted density is not lost, and the energy density of the battery can be further improved.
In a word, based on the specific structure, the synergistic effect among the graphite core layer, the amorphous carbon shell layer and the carbon nanotube layer is better, and the matching property between the modified graphite particles and the hard carbon is better, so that the lithium ion battery formed by the negative electrode material can simultaneously give consideration to better quick charge performance, low temperature performance, energy density and cycle performance.
In a preferred embodiment, the thickness of the amorphous carbon shell layer in the negative electrode material of the present invention is 50 to 150nm, and the weight content of the amorphous carbon shell layer is 3 to 8wt%. The thickness of the amorphous carbon shell layer in the negative electrode material is limited in the range, so that the lithium ion releasing and inserting channels in the lithium ion battery prepared from the modified graphite negative electrode material can be remarkably increased, and the primary efficiency of the battery can not be greatly sacrificed, so that the primary efficiency and the quick charging performance of the battery are further balanced.
More preferably, the thickness of the carbon nanotube layer in the anode material is defined to be 20-80 nm, and the weight content of the carbon nanotube layer is 3-8 wt%. Based on this, the conductivity of the battery is better. Meanwhile, the carbon nanotube layer with the thickness can further promote the stability of the three-dimensional network structure to be better, so that the overall conductivity of the cathode material is improved, the migration impedance can be reduced, and the rate capability, the quick charge performance and the low-temperature performance of the battery are improved.
In order to better match the particle size of the modified graphite particles with the particle size range of the graphite core layer, the energy density and electrochemical performance of the battery can be further balanced. More preferably, the Dv50 particle diameter of the graphite core layer is 10 to 20 μm, and the Dv50 particle diameter of the modified graphite particle is 10.0 to 20.5 μm, preferably 10 to 16 μm.
In order to further promote the close packing between the modified graphite particles and the hard carbon particles, the compact density is not lost, and the energy density of the battery is further improved. In the negative electrode material, the weight content of the hard carbon is preferably 1 to 10wt%; it is further preferable that the modified graphite particles are contained in an amount of 90 to 99wt%.
Further preferably, the graphitization degree of the modified graphite particles in the negative electrode material of the present invention is not less than 92%. Based on the method, gram capacity and first efficiency (namely energy density) can be ensured, and dynamic performance can be considered. More preferably, the degree of graphitization of the modified graphite particles is 93 to 95%. The gram capacity of the modified graphite particles is further optimized to further ensure the energy density in the lithium ion battery, and the gram capacity of the modified graphite particles is more than or equal to 350mAh/g; more preferably, the modified graphite particles have a gram capacity of 355 to 360mAh/g.
More preferably, the hard carbon in the negative electrode material of the present invention is in the form of particles, and the Dv50 particle size of the hard carbon is 3 to 6 μm. In order to better match the particle size of the hard carbon particles with the particle size of the modified graphite particles, the particle size of the hard carbon is preferably in the above range, which can facilitate more effective "caulking" of the small hard carbon particles in the gaps between the large modified graphite particles, thereby better improving the packing between the modified graphite particles and the hard carbon particles, so as not to lose the compaction density of the modified graphite particles, and further better improving the energy density of the battery.
In order to better promote the competitiveness of circulation and cyclic expansion in the negative electrode material and simultaneously greatly improve the quick charge performance of the battery and reduce the loss of energy density, the gram capacity of the hard carbon is further optimized, and the gram capacity of the hard carbon is more than or equal to 380mAh/g. More preferably, the hard carbon has a gram capacity of 395 to 420mAh/g.
More preferably, the negative electrode material has a defect degree of 0.3 to 0.6. The more defects of the negative electrode material, the more the active sites can be gradually increased, so that lithium ions can be more conveniently separated from and embedded into the channel in the charging and discharging process of the battery, and more vacancies are formed on the surface of the negative electrode material to store the lithium ions when the battery is charged at a high rate (the positive electrode is separated from more lithium ions), so that the buffering effect is achieved, and the battery has better rate capability and quick charging capability. More preferably, the defect degree of the electrode material is 0.40 to 0.55, and excessive defects may cause excessive lithium ion consumption of the battery during the first charge to form the SEI film, may cause low first efficiency of the battery, and may decrease the energy density of the battery.
The invention also provides a preparation method of the cathode material, which comprises the following steps: providing a graphite core layer, coating an amorphous carbon shell layer on the outer surface of the graphite core layer, coating a carbon nanotube layer on the outer surface of the amorphous carbon shell layer far away from the graphite core layer so as to obtain modified graphite particles, and finally mixing the modified graphite particles with hard carbon to obtain the cathode material.
For one of the reasons mentioned above, the present invention adopts graphite as a core layer, and coats an amorphous carbon shell layer on the outer surface of the graphite core layer, where the amorphous carbon shell layer can significantly increase the surface defect degree of the modified graphite particles, and further promotes the surface of the modified graphite particles to have active sites, and these active sites can make lithium ions more conveniently come out of and insert into channels during the charging and discharging processes of the battery, and especially when the battery is charged at a large rate (the positive electrode comes out of more lithium ions), these active sites can form a large number of vacancies to store lithium ions, so as to play a role of buffering, and further make the quick charging performance of the battery more excellent (i.e. when the battery is charged at a short time and a large rate, the battery can maintain excellent electrochemical performance). Secondly, the outer surface of the amorphous carbon shell layer is further coated with a carbon nano tube layer, the carbon nano tube layer has good electric conductivity, and point and line contacts among modified graphite particles and between the modified graphite and hard carbon can be increased, so that an electronic conductive three-dimensional network can be constructed and formed, the overall electric conductivity of the negative electrode material is improved, the migration impedance is reduced, and the rate capability, the quick charge performance and the low-temperature performance of the battery are improved. Thirdly, the modified graphite particles are further mixed with hard carbon to form the negative electrode material, the hard carbon has the characteristics of high multiplying power, good cycle and low expansion, and the hard carbon is mixed with the modified graphite to prepare the negative electrode material, so that the multiplying power performance, the quick charge performance and the low temperature performance of the lithium ion battery can be greatly improved, and the cycle performance of the battery is also obviously improved. And moreover, the hard carbon is dispersedly arranged in gaps of the modified graphite particles to be filled, so that the close packing among the particles can be ensured, the compacted density is not lost, and the energy density of the battery can be further improved.
In a preferred embodiment, the method for preparing the anode material includes: step S1: crushing graphite, and then carrying out first sintering to obtain a graphite nuclear layer; step S2: mixing the graphite core layer and the carbon coating agent, and performing second sintering to coat the amorphous carbon shell layer on the outer surface of the graphite core layer to obtain graphite particles coated with the amorphous carbon shell layer; and step S3: mixing the graphite particles coated with the amorphous carbon shell layer and a carbon nano tube coating agent, and performing third sintering to coat the carbon nano tube layer on the outer surface of the amorphous carbon shell layer, which is far away from the graphite core layer, so as to obtain modified graphite particles; and step S4: and mixing the modified graphite particles with hard carbon by adopting a mechanical ball milling mode to obtain the cathode material.
One skilled in the art may first crush the graphite and then perform a first sintering to obtain a graphite core layer. Then, the graphite core layer and the carbon coating agent are mixed and subjected to second sintering to coat the amorphous carbon shell layer on the outer surface of the graphite core layer, thereby obtaining the graphite particles coated with the amorphous carbon shell layer. And then, mixing the graphite particles coated with the amorphous carbon shell layer and a carbon nano tube coating agent, and performing third sintering to coat the carbon nano tube layer on the outer surface of the amorphous carbon shell layer far away from the graphite core layer, thereby obtaining the modified graphite particles. Finally, those skilled in the art can mix the modified graphite particles with hard carbon by means of mechanical ball milling to obtain the final negative electrode material. The cathode material prepared by the preparation method has better electrochemical performance, can greatly improve the quick charge performance, the low-temperature performance and the energy density of the lithium ion battery, and obviously improves the cycle performance of the battery. The preparation method has the advantages of simple flow and easy operation, thereby better promoting the large-scale production of the cathode material and further leading the industrial application prospect of the cathode material to be wider.
In order to further improve the stability of the sintering process and to better balance the fast charging performance, the cycling performance, the energy density and the low temperature performance of the battery, the first sintering in step S1 is performed in a graphitization furnace at a first sintering temperature > 2400 ℃, preferably 2400-3000 ℃.
In order to better coat the amorphous carbon shell layer on the outer surface of the graphite core layer, the electrochemical performance of the negative electrode material is further improved, and the quick charge performance, the cycle performance, the energy density and the low-temperature performance of the battery are better improved. The carbon coating agent in step S2 is selected from the group consisting of asphalt having a softening point temperature of 250 to 280 ℃. More preferably, the carbon coating agent is used in an amount of 3 to 8wt% based on the weight of the graphite core layer. In order to further improve the stability of the sintering process, the sintering temperature of the second sintering is preferably 600-800 ℃, the heating rate from the normal temperature to the second sintering temperature is preferably 0.5-2 ℃/min, and the second sintering time is preferably 2-6 h.
In order to better coat the carbon nanotube layer on the outer surface of the amorphous carbon shell layer away from the graphite core layer, thereby further improving the electrochemical performance of the negative electrode material, and better improving the quick charge performance, the cycle performance, the energy density and the low-temperature performance of the battery, the carbon nanotube coating agent in the step S3 comprises a carbon-containing binder and carbon nanotubes. Those skilled in the art can obtain a carbon layer coated with carbon nanotubes on the outer surface of the amorphous carbon shell layer away from the graphite core layer after performing a third sintering on the carbon nanotube coating agent and the graphite particles coated with the amorphous carbon shell layer. More preferably, the carbonaceous binder is selected from the group consisting of asphalts having a softening point temperature of 180 to 230 ℃. More preferably, the carbon nanotubes are selected from multi-wall carbon nanotubes and/or single-wall carbon nanotubes, and the length-diameter ratio of the carbon nanotubes is (50-100): 1. In order to further improve the stability of the sintering process, the sintering temperature of the third sintering is limited to be 600-800 ℃, the heating rate from the normal temperature to the third sintering temperature is 0.5-2 ℃/min, and the third sintering time is 2-6 h. More preferably, the carbon nanotube coating agent is used in an amount of 3 to 8wt% based on the weight of the graphite particles coated with the amorphous carbon shell layer. More preferably, the weight ratio of the carbon-containing binder to the carbon nanotubes in the carbon nanotube coating agent is (1 to 1.5): 1.
In order to better enable hard carbon to be uniformly dispersed among the modified graphite particles, thereby further improving the electrochemical performance of the negative electrode material, and further improving the quick charge performance, the cycle performance, the energy density and the low-temperature performance of the battery. The weight ratio of the modified graphite particles to the hard carbon is defined as (99-90): (1-10), the modified graphite particles and the hard carbon are preferably mixed by mechanical running-in, and the rotation speed during mechanical running-in is more preferably 50-150 rpm.
The invention also provides a negative electrode coating which comprises a negative electrode material, a binder and a dispersing agent, wherein the negative electrode material is the negative electrode material or the negative electrode material obtained by the preparation method of the negative electrode material.
When the negative electrode material is used as a negative electrode coating, the battery can have excellent quick charging performance under the condition of not adding a conductive agent. Of course, a person skilled in the art can also select a small amount of conductive agent to further improve the quick-charging performance. The amount of the conductive agent in the negative electrode coating can be 0-2.5 wt%.
The invention also provides a negative pole piece which comprises a coating and a base material, wherein the coating is obtained by coating and molding the negative pole coating.
In a preferred embodiment, the aforementioned coating can be applied to a substrate by one skilled in the art on a single side, preferably with a coating weight of 6.5 to 13.0mg/cm 2 . After coating, the technical personnel in the field can adopt a rolling mode to carry out forming treatment, and the compacted density of the rolled negative electrode and pole piece is 1.60-1.75 g/cm 3 . Based on the method, the porosity of the pole piece can be further improved, the electrolyte infiltration is promoted, and the multiplying power and the quick charging performance of the battery are further improved.
The invention also provides a lithium ion battery which comprises the negative pole piece. Based on the reasons, the lithium ion battery has better electrochemical performance, and has better quick charge performance, energy density, low-temperature performance and cycle performance.
The present application is described in further detail below with reference to specific examples, which should not be construed as limiting the scope of the invention as claimed.
Example 1
The preparation method of the negative electrode material comprises the following steps:
step S1: crushing graphite, placing the crushed graphite in a graphitization furnace, and performing first sintering at the first sintering temperature of 2400-2600 ℃ to obtain a graphite core layer. Wherein the Dv50 particle size of the graphite core layer is 14 μm.
Step S2: and mixing the graphite core layer and the carbon coating agent for second sintering, wherein the second sintering temperature is 650 ℃, the temperature rise speed is 1 ℃/min, and the second sintering time is 3h. The carbon coating agent is selected from asphalt with the softening point temperature of 250 ℃, and the using amount of the carbon coating agent accounts for 5% of the weight of the graphite core layer, so that an amorphous carbon shell layer is coated on the outer surface of the graphite core layer to obtain the graphite particles coated with the amorphous carbon shell layer, and the thickness of the amorphous carbon shell layer is 100-120 nm (the maximum thickness of the amorphous carbon shell layer is not more than 120nm, and the minimum thickness of the amorphous carbon shell layer is not less than 100 nm).
And step S3: and mixing the graphite particles coated with the amorphous carbon shell layer and the carbon nano tube coating agent for third sintering, wherein the third sintering temperature is 650 ℃, the temperature rising speed is 1 ℃/min, and the third sintering time is 3h. The carbon nanotube coating agent comprises a carbon-containing binder and a carbon nanotube, wherein the carbon-containing binder is selected from pitch with the softening point temperature of 190 ℃, the carbon nanotube is a single-walled carbon nanotube, the length-diameter ratio of the carbon nanotube is (70-80): 1, the weight ratio of the carbon-containing binder to the carbon nanotube is 4. And coating a carbon nanotube layer on the outer surface of the amorphous carbon shell layer far away from the graphite core layer to obtain the modified graphite particles. The thickness of the carbon nano tube layer is 45-60 nm (the maximum thickness of the carbon nano tube layer is not more than 60nm, and the minimum thickness is not less than 45 nm).
The graphitization degree of the modified graphite particles is 93.5%, the gram capacity of the modified graphite particles is 356mAh/g, and the Dv50 particle size of the modified graphite particles is 14.0 mu m.
And step S4: and mixing the modified graphite particles with hard carbon by adopting a mechanical ball milling mode (the ball milling rotation speed is 80 rpm), screening, and carrying out ball milling and shaping to obtain the cathode material. Wherein the weight ratio of the modified graphite particles to the hard carbon is 93.
In the finally obtained negative electrode material, the modified graphite particles were 93wt%, the hard carbon was 7wt%, and the degree of defect was 0.5.
The preparation method of the negative electrode coating comprises the following steps:
the negative electrode material, the dispersant CMC, and the binder SBR were mixed at a weight ratio of 96.
The preparation method of the negative pole piece comprises the following steps:
coating the negative electrode coating on a copper foil base material for double-sided coating, wherein each single-sided coating weight is 9.0mg/cm 2 Then rolling is carried out, and the compacted density of the rolled negative pole piece is 1.65g/cm 3 。
Example 2
The only difference from example 1 is that the weight ratio of the modified graphite particles to the hard carbon in step S4 was 96.
In the finally obtained anode material, the weight content of hard carbon was 4wt%, the weight content of modified graphite particles was 96wt%, and the degree of defect was 0.43.
Example 3
The only difference from example 1 is that the weight ratio of the modified graphite particles to the hard carbon in step S4 is 99.
In the finally obtained negative electrode material, the hard carbon content was 1wt%, the modified graphite particles were 99wt%, and the degree of defect was 0.40.
Example 4
The only difference from example 1 is that the weight ratio of the modified graphite particles to the hard carbon in step S4 is 90.
In the finally obtained anode material, the weight content of hard carbon was 10wt%, the weight content of modified graphite particles was 90wt%, and the degree of defect was 0.54.
Example 5
The difference from example 1 is only that the amount of the carbon covering agent in step S2 is 3wt% based on the weight of the graphite core layer.
In the finally obtained negative electrode material, the defect degree is 0.47, and the thickness of the amorphous carbon shell layer is 60-80 nm (the maximum thickness of the amorphous carbon shell layer is not more than 80nm, and the minimum thickness is not less than 60 nm).
Example 6
The difference from example 1 is only that the amount of the carbon covering agent in step S2 is 8wt% based on the weight of the graphite core layer.
In the finally obtained negative electrode material, the defect degree is 0.52, and the thickness of the amorphous carbon shell layer is 130-150 nm (the maximum thickness of the amorphous carbon shell layer is not more than 150nm, and the minimum thickness is not less than 130 nm).
Example 7
The only difference from example 1 is that the amount of the carbon nanotube coating agent used in step S3 is 3wt% based on the weight of the graphite particles coated with the amorphous carbon shell layer.
In the finally obtained cathode material, the defect degree is 0.45, and the thickness of the carbon nanotube layer is 20-36 nm (the maximum thickness of the carbon nanotube layer is not more than 36nm, and the minimum thickness is not less than 20 nm).
Example 8
The only difference from example 1 is that the amount of the carbon nanotube coating agent used in step S3 is 8wt% based on the weight of the graphite particles coated with the amorphous carbon shell layer.
In the finally obtained cathode material, the defect degree is 0.52, and the thickness of the carbon nanotube layer is 65-80 nm (the maximum thickness of the carbon nanotube layer is not more than 80nm, and the minimum thickness is not less than 65 nm).
Comparative example 1
Crushing a graphite raw material to obtain graphite particles with a Dv50 particle size of 14.0 mu m of a graphite core layer, then placing the graphite particles in a graphitization furnace for sintering at a sintering temperature of 2550-2600 ℃, so as to obtain graphite particles containing the graphite core layer, wherein the graphitization degree is 93.5%, directly screening and ball-milling and shaping to obtain the negative electrode material, and the defect degree is 0.15.
Comparative example 2
Crushing a graphite raw material to obtain graphite particles with a Dv50 particle size of 14.0 mu m of a graphite core layer, and then placing the graphite particles into a graphitization furnace for sintering at the sintering temperature of 2400-2600 ℃, so as to obtain the graphite particles containing the graphite core layer, wherein the graphitization degree is 93.5%. Then, 7wt% of hard carbon having a Dv50 particle size of 4.5 μm and a gram volume of 400mAh/g was added. The defectivity of the anode material was 0.30.
Comparative example 3
The difference from example 1 is that without step S4, the anode material had a defect degree of 0.25.
Comparative example 4
The only difference from example 1 is that the weight ratio of the modified graphite particles to the hard carbon in step S4 is 85.
In the finally obtained negative electrode material, the hard carbon content was 15wt%, the modified graphite particles were 85wt%, and the degree of defect was 0.68.
Comparative example 5
The difference from example 1 is only that the amount of the carbon covering agent in step S2 is 15wt% based on the weight of the graphite core layer.
In the finally obtained negative electrode material, the defect degree is 0.59, and the thickness of the amorphous carbon shell layer is 200-220 nm (the maximum thickness of the amorphous carbon shell layer is not more than 220nm, and the minimum thickness is not less than 200 nm).
Comparative example 6
The only difference from example 1 is that the amount of the carbon nanotube coating agent in step S3 is 1wt% based on the weight of the graphite particles coated with the amorphous carbon shell layer.
In the finally obtained cathode material, the defect degree is 0.40, and the thickness of the carbon nanotube layer is 1-35 nm (the maximum thickness of the carbon nanotube layer is not more than 35nm, and the minimum thickness is not less than 1 nm).
Comparative example 7
The only differences from example 1 were that the Dv50 particle size of the modified graphite particles was 8.0 μm, the Dv50 particle size of the hard carbon was 8 μm, and the degree of defect of the anode material was 0.28.
And (3) performance testing:
and assembling the negative pole pieces prepared in the above embodiments and comparative examples into a battery, and further testing the performance of the lithium ion battery.
(1) Quick filling (multiplying power) performance
The test was carried out using a high and low temperature cabinet apparatus, and the test result was the ratio of the capacity of a 0.2C charged battery at a temperature of 25℃ to the capacity of a 2C charged battery at a temperature of 25℃.
(2) Cycle performance
The charge and discharge capacity of battery 1C was attenuated to 80% of the initial capacity for the number of cycles.
(3) Low temperature performance
The test was carried out using a high and low temperature cabinet apparatus to test the ratio of the cell capacity at 25 ℃ for 0.5C discharge to the cell capacity at-10 ℃ for 0.1C discharge.
(4) Degree of defect
Measured by Raman spectroscopy, the test anode material has a Raman spectrum of 1250cm -1 To 1650cm -1 Peak intensity Id of (A) and hard carbon at a spectrum of 1500cm -1 To 1650cm -1 The ratio of the peak intensities Ig of (a).
(5) Energy density
Volume energy density (Wh/L) = lithium battery capacity (mAh) × voltage (V)/(thickness (cm) × width (cm) × length (cm)), lithium battery capacity = active material weight (g) × gram capacity × first efficiency, and in the present invention, the level of energy density is comprehensively evaluated as a result of gram capacity and first efficiency.
Specifically, the performance test results are shown in table 1 below:
TABLE 1
From the above description, it can be seen that the above-described embodiments of the present invention achieve the following technical effects:
from the test results of examples 1, 2, 3, 4 and comparative example 4, it can be found that when the weight ratio of the modified graphite particles to the hard carbon is (99-90) to (1-10) (e.g. 93 of example 1, 96 of example 2, 99 of example 3, and 90 of example 4. And when the weight ratio of the modified graphite particles to the hard carbon is out of the range of (99-90): (1-10) (such as 85 of comparative example 4).
From the test results of examples 1, 5 and 6 and comparative example 5, it can be seen that when the amount of the carbon coating agent is in the range of 3 to 8wt% of the graphite core layer (e.g., 4wt% of example 1, 3wt% of example 5, and 8wt% of example 6), the prepared lithium ion battery has good fast charge performance, low temperature performance, and cycle performance, and good overall performance. When the amount of the carbon coating agent is out of the range of 3-8 wt% of the weight of the graphite core layer (for example, 15wt% of comparative example 5), the prepared battery has poor low-temperature performance and cycle performance due to the fact that the thickness of the amorphous carbon shell layer is too thick, the defect degree is high, and meanwhile, too much lithium ions are consumed to form an SEI film during the first charging and discharging, the first efficiency is low, the formed film is too thick, the impedance is increased, and side reactions generated during the repair of the SEI film in the cycle process are more.
From the test results of examples 1, 7, 8 and comparative example 6, it can be seen that when the amount of the carbon nanotube coating agent is in the range of 3 to 8wt% based on the weight of the graphite core layer (e.g., 7wt% for example 1, 3wt% for example 7, and 8wt% for example 8), the prepared lithium ion battery has good fast charge performance, low temperature performance, and cycle performance. When the amount of the carbon nanotube coating agent is out of the range of 3 to 8wt% of the weight of the graphite core layer (e.g., 1wt% of comparative example 6), the prepared battery has poor quick charge performance, poor low temperature performance and poor cycle performance due to the low carbon nanotube coating agent ratio, non-uniform film thickness and large film thickness range.
From the test results of example 1 and comparative example 1, it can be found that when the negative electrode material prepared using the modified graphite particles of the present invention and the hard carbon dispersed between the modified graphite particles is used as a battery, it has advantages of good fast charge performance, low temperature performance, energy density, and cycle performance. And the performance of the battery is poorer because the cathode material is prepared by only adopting the conventional graphite.
From the test results of example 1 and comparative example 2, it can be found that when the negative electrode material prepared using the modified graphite particles of the present invention and the hard carbon dispersed between the modified graphite particles has advantages of better fast charge performance, low temperature performance, energy density, and cycle performance when used as a battery, compared to conventional graphite.
From the test results of example 1 and comparative example 3, it can be found that when the negative electrode material prepared by using the modified graphite particles of the present invention and the hard carbon dispersed between the modified graphite particles is compared with the negative electrode material prepared by using the modified graphite material without adding the hard carbon, the lithium ion battery prepared by the present invention has the advantages of better fast charge performance, low temperature performance, energy density and cycle performance.
From the test results of example 1 and comparative example 7, it was found that the lithium ion battery prepared using the modified graphite particles of the present invention has advantages of good quick charge performance, low temperature performance, energy density, and cycle performance when the Dv50 particle size is within the range of 10.0 to 20.5 μm (e.g., 14 μm of example 1), while the battery performance is poor when the Dv50 particle size of the modified graphite particles is within the range of 10.0 to 20.5 μm (e.g., 8 μm of comparative example 7).
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (14)
1. An anode material, characterized in that the anode material comprises modified graphite particles and hard carbon dispersed between the modified graphite particles, and the particle size of the modified graphite particles is larger than that of the hard carbon; wherein the modified graphite particles comprise:
a graphite core layer;
an amorphous carbon shell layer coated on the outer surface of the graphite core layer;
and the carbon nanotube layer is coated on the outer surface of the amorphous carbon shell layer far away from the graphite core layer.
2. The negative electrode material as claimed in claim 1, wherein the thickness of the amorphous carbon shell layer of the modified graphite particles is 50-150 nm;
preferably, the thickness of the carbon nanotube layer is 20-80 nm;
preferably, the Dv50 particle size of the graphite core layer is 10 to 20 μm;
preferably, the Dv50 particle size of the modified graphite particles is in the range of 10.0 to 20.5 μm, preferably 10 to 16 μm.
3. The negative electrode material according to claim 1 or 2, wherein the weight content of the hard carbon in the negative electrode material is 1 to 10wt%;
preferably, the weight content of the modified graphite particles is 90 to 99wt%.
4. The negative electrode material of any one of claims 1 to 3, wherein the modified graphite particles have a graphitization degree of 92% or more, preferably 93-95%;
preferably, the gram capacity of the modified graphite particles is more than or equal to 350mAh/g, and preferably 355-360 mAh/g.
5. The negative electrode material according to any one of claims 1 to 4, characterized in that the Dv50 particle size of the hard carbon is 3 to 6 μm;
preferably, the gram capacity of the hard carbon is more than or equal to 380mAh/g, preferably 395-420 mAh/g;
preferably, the negative electrode material has a defect degree of 0.30 to 0.60, preferably 0.40 to 0.55.
6. A production method of the anode material according to any one of claims 1 to 5, comprising:
providing a graphite core layer;
coating an amorphous carbon shell layer on the outer surface of the graphite core layer;
coating a carbon nanotube layer on the outer surface of the amorphous carbon shell layer far away from the graphite core layer to obtain modified graphite particles;
and mixing the modified graphite particles with hard carbon to obtain the negative electrode material.
7. The method for preparing the anode material according to claim 6, comprising the steps of:
step S1: crushing graphite and then performing first sintering to obtain the graphite nuclear layer;
step S2: mixing the graphite core layer and a carbon coating agent, and performing second sintering to coat the amorphous carbon shell layer on the outer surface of the graphite core layer to obtain graphite particles coated with the amorphous carbon shell layer;
and step S3: mixing the graphite particles coated with the amorphous carbon shell layer and a carbon nano tube coating agent, and performing third sintering to coat the carbon nano tube layer on the outer surface of the amorphous carbon shell layer far away from the graphite core layer to obtain the modified graphite particles;
and step S4: and mixing the modified graphite particles with the hard carbon to obtain the negative electrode material.
8. The method for preparing the negative electrode material according to claim 7, wherein the first sintering in step S1 is performed in a graphitization furnace, and the first sintering temperature is 2400 ℃ or more, preferably 2400 to 3000 ℃.
9. The method according to any one of claims 7 and 8, wherein the carbon coating agent in step S2 is selected from pitch having a softening point temperature of 250 to 280 ℃;
preferably, the amount of the carbon coating agent is 3-8 wt% of the weight of the graphite core layer;
preferably, the sintering temperature of the second sintering is 600-800 ℃, and the second sintering time is 2-6 h.
10. The method according to any one of claims 7 to 9, wherein the carbon nanotube coating agent in step S3 includes a carbon-containing binder and carbon nanotubes;
preferably, the carbonaceous binder is selected from the group consisting of bitumen having a softening point temperature of 180 to 230 ℃;
preferably, the carbon nanotubes are selected from multi-wall carbon nanotubes and/or single-wall carbon nanotubes, and the length-diameter ratio of the carbon nanotubes is (50-100): 1;
preferably, the sintering temperature of the third sintering is 600-800 ℃, and the third sintering time is 2-6 h;
preferably, the amount of the carbon nano tube coating agent is 3 to 8wt% of the weight of the graphite particles coated with the amorphous carbon shell layer;
more preferably, in the carbon nanotube coating agent, the weight ratio of the carbon-containing binder to the carbon nanotubes is (1 to 1.5): 1.
11. The method for producing the anode material according to any one of claims 7 to 10, wherein the weight ratio of the modified graphite particles to the hard carbon in the step S4 is (99 to 90): (1 to 10);
preferably, the modified graphite particles are mixed with the hard carbon in a mechanical running-in manner;
more preferably, the rotational speed in the mechanical running-in is 50 to 150rpm.
12. The negative electrode coating is characterized by comprising a negative electrode material, a binder and a dispersing agent, wherein the negative electrode material is the negative electrode material in any one of claims 1 to 5 or the negative electrode material prepared by the preparation method of the negative electrode material in any one of claims 6 to 11.
13. A negative pole piece is characterized by comprising a coating and a base material, wherein the coating is obtained by coating and molding the negative pole coating of claim 12.
14. A lithium ion battery, characterized in that the lithium ion battery comprises the negative electrode tab of claim 13.
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