CN112582589B - Silicon-graphite composite negative electrode material, preparation method and lithium ion battery prepared from silicon-graphite composite negative electrode material - Google Patents
Silicon-graphite composite negative electrode material, preparation method and lithium ion battery prepared from silicon-graphite composite negative electrode material Download PDFInfo
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Abstract
The invention relates to a silicon-graphite composite negative electrode material, a preparation method and a lithium ion battery prepared from the silicon-graphite composite negative electrode material. According to the composite anode material, the local small particles are uniformly wrapped, and the structure of the whole large particles which are firmly supported relieves polarization phenomena in the charge and discharge process caused by poor conductivity, volume effect and agglomeration effect of the silicon-based material, so that the direct current internal resistance in charge and discharge is effectively reduced. The composite negative electrode is used for a lithium ion secondary battery and has the characteristics of high capacity, high coulombic efficiency, long cycle life, low charge-discharge direct current internal resistance and the like.
Description
Technical Field
The invention belongs to the technical field of lithium batteries, and particularly relates to a silicon-graphite composite negative electrode material, a preparation method and a lithium ion battery prepared from the silicon-graphite composite negative electrode material.
Background
In recent years, with the development of new energy electric vehicles and portable wearable electronic devices, there is an increasing demand for lithium ion secondary batteries having high energy density, high safety and long cycle life. The lithium ion battery is assembled by a positive electrode, a negative electrode, a diaphragm and electrolyte, wherein each part is required to be evaluated and optimized, and although a positive electrode material with higher operability and high capacity potential is the research and development focus in the current academia and industry, a negative electrode material which can be matched with the positive electrode material is not ignored.
Currently, the commercial lithium ion battery cathode material is mainly graphite, but the lower theoretical capacity (372 mAh/g) limits the further improvement of the energy density of the lithium ion battery. The silicon-based material has very high theoretical capacity (4200 mAh/g), and has incomparable capacity advantage when being applied to a negative electrode. However, current silicon materials also face a great challenge as lithium ion battery anode materials, and the bottlenecks limiting their development are as follows: (1) The silicon material generates alloying/dealloying reaction in the charging and discharging process to cause huge volume change (about 300 percent), the material generates mechanical damage on the structure, the materials are pulverized and separated, and fall off from a current collector, so that the capacity is rapidly attenuated; (2) The volume effect of silicon makes it difficult to form a stable SEI film, the SEI film is formed continuously from the fresh surface formed by expanding and crushing particles, lithium ions and electrolyte are consumed continuously, and extremely low coulomb efficiency is caused; (3) The silicon material has poor conductivity, serious polarization phenomenon in the charge and discharge process and severe volume effect in the charge and discharge process, so that the original constructed conductive network is broken. Meanwhile, due to the agglomeration effect of the silicon-based material, broken silicon-based particles with high surface energy tend to mutually agglomerate, and local heterogeneity is remarkably increased, so that the charge-discharge direct current internal resistance is continuously and irreversibly increased. The high internal resistance of the material in the direct current of charge and discharge tends to make the thermal effect of the current more remarkable, and the thermal stability of the manufactured battery in charge and discharge is reduced, especially under high current density, so that the aging degree and the safety performance of the battery are challenged.
In recent years, no matter the modification of the silicon material, such as silicon nanocrystallization, design of a silicon composite material, and application of some silicate, or the improvement of a battery end, such as development of novel binders and electrolytes, prelithiation, and the like, the effects of the capacity improvement first effect and the lower direct current internal resistance expected by the strategies are not ideal, the silicon material is not truly popularized and put into practical use, and the root causes are the inefficiency and high cost of the strategies.
A compromise is made by directly blending silicon and graphite in a certain proportion without modification. Compared with a pure graphite electrode, the slightly low silicon content realizes larger performance improvement, the volume effect liquid of silicon can be relieved to the greatest extent by the pore structure created by graphite particles, the problem of poor silicon conductivity is solved, and the stability is ensured and the large jump of performance is realized. The method is simple and easy to operate and low in cost, and is a mode which is mostly adopted in the industry at present. However, the particle effects of the two different active components are mutually influenced, and the interdependence between the silicon particle content and the graphite particle size in the silicon-graphite electrode directly influences the alleviation degree of the silicon particle volume effect and the agglomeration effect, thereby influencing the coulomb efficiency, the cycle life and the charging direct current internal resistance of the prepared electrode.
On the other hand, safety, stability and reliability are the necessary characteristics of the manufactured battery, and to achieve this objective, it is necessary to control the whole process of material preparation and battery manufacturing. The thermal performance evaluation of the anode and cathode materials is an extremely important ring, and the direct current internal resistance of charge and discharge is one of important indexes of the reaction parameter. The charging direct current internal resistance of the manufactured pole piece directly represents the polarization resistance (comprising electrochemical polarization resistance and concentration polarization resistance) of the battery. If the internal resistance of the pole piece is larger, the thermal effect of the current is more remarkable, the thermal stability of the battery during charging and discharging is reduced, and particularly under the condition of high current density, so that the aging degree and the safety performance of the battery are challenged.
CN111416098A discloses a preparation method of a lithium ion battery anode, the active material layer of the anode contains an active material composed of a mixture of graphite particles and silicon particles, wherein the graphite particles comprise first graphite particles and second graphite particles, the particle size D50 of the first graphite particles is 3.2-3.5 microns, the particle size D50 of the second graphite particles is 1.5-1.7 microns, and the particle size D50 of the silicon particles is 1.2-1.5 microns. According to the invention, the bottom layer slurry, the middle layer slurry and the surface layer slurry are prepared according to different proportions, so that the anode obtained by the preparation method has higher energy density and rate capability and better cycle stability. CN111554899a discloses a mixing method of a negative electrode slurry, which comprises first graphite particles, second graphite particles and silicon particles, wherein the average particle diameter D50 of the first graphite particles is 2.3-2.5 micrometers, the D50 of the second graphite particles is 0.4-0.5 times of the first graphite particles, the particle diameter D50 of the silicon particles is 360-400nm, and the mass ratio of the first graphite particles, the second graphite particles and the silicon particles is 100:15-17:30-35. According to the invention, a step-by-step mixing method is adopted, first graphite particles and second graphite particles are pulped, then silicon particles are added into the slurry to obtain the electrode slurry, the storage time of the electrode slurry is long, the retention property is good, the coating property is good, and the obtained negative electrode has higher energy density and stability. In the prior art, the particle size distribution of two graphite particles is relatively close, and the volume effect and agglomeration effect of silicon particles in the charging and discharging process still cannot be well inhibited, so that the internal resistance of direct current polarization is increased.
Therefore, the existing negative electrode material still needs to be optimized, so that the obtained negative electrode has higher energy density and cycle stability, and meanwhile, the charge-discharge direct current internal resistance of the negative electrode material is reduced, so that the safety of the battery is improved.
Disclosure of Invention
The invention aims to provide a composite anode material with different particle size distribution and size of graphite particles and silicon particles, which is used for lithium ion secondary batteries and has the characteristics of high coulombic efficiency, long cycle life and low charge-discharge direct current internal resistance.
The invention further aims at providing a preparation method of the silicon-graphite composite anode material.
It is still another object of the present invention to provide a lithium ion battery made of such a silicon-graphite composite anode material.
A silicon-graphite composite negative electrode material comprises silicon particles and graphite particles, wherein the silicon particles are uniformly dispersed in a graphite phase consisting of the graphite particles to form composite particles; the graphite particles are composed of two kinds of graphite particles having different particle size distributions, the D50 of the graphite particles being 1 μm to 100 μm, wherein the large-size graphite particles have a particle diameter of 20 μm to 100 μm in D50, and the small-size graphite particles have a particle diameter of 1 μm to 20 μm in D50.
In a specific embodiment, the silicon particles are present in the composite particles in a mass ratio of 1% to 50% and the graphite particles are present in the composite particles in a mass ratio of 50% to 99%.
In a specific embodiment, the mass ratio of the large-size graphite particles in the composite particles is 40% -98.5%, wherein the mass ratio of the small-size graphite particles in the composite particles is 0.5% -59%.
In a specific embodiment, the silicon particles are Si, siO 2 And any one or more of SiO.
In a specific embodiment, the silicon particles have a particle size with a D50 of 1 μm to 30. Mu.m, preferably 1 μm to 10. Mu.m.
In another aspect of the present invention, in the preparation method of the silicon-graphite composite negative electrode material, the silicon particles and the graphite particles are mixed in a mechanical mixing manner to obtain the silicon-graphite composite negative electrode material; preferably, the mechanical mixing mode is selected from one or more of a mechanical fusion machine, a mixer, a ball mill, a high-speed mixer, a high-speed disperser and a jet mill.
In yet another aspect of the present invention, a lithium ion battery is made from the negative electrode of the lithium ion battery made of the silicon-graphite composite negative electrode material.
In a specific embodiment, the dispersing agent used in the preparation process of the lithium ion battery cathode is selected from any one or more of water, methanol, ethanol, isopropanol, N-butanol, diethyl ether, acetone, N-methylpyrrolidone, benzene, toluene, xylene, N-dimethylformamide and chloroform.
In a specific embodiment, the binder used in the preparation process of the lithium ion battery anode is selected from any one or more of styrene-butadiene rubber emulsion, sodium hydroxymethyl cellulose, polyacrylic acid, polyacrylonitrile, polyacrylate and polyvinylidene fluoride.
In a specific embodiment, the conductive agent used in the preparation process of the lithium ion battery anode is selected from any one or more of Super P, acetylene black, natural graphite, artificial graphite, ketjen black, carbon nanotubes, graphene, carbon fibers and fullerene.
Compared with the prior art, the technical scheme of the invention has the following beneficial effects:
1) The silicon-graphite composite anode material is formed by combining large-size and small-size graphite particles with different particle size distributions, and silicon particles with a certain proportion are uniformly dispersed in a graphite phase. The small-size graphite particles and the silicon particles are mixed to be prone to a compact stacking mode, so that continuity of electron and ion transmission among the silicon particles is realized, a role of a conductive network can be well played, and the problem of poor conductivity of silicon is solved; the porous structure formed by stacking large-size graphite particles can provide sufficient stress for the alloying/dealloying reaction of silicon, and the problem of poor electrode stability caused by volume effect is solved. The local small particles are uniformly wrapped, the whole large particles are firmly supported, the poor conductivity, the volume effect and the mutual agglomeration of broken silicon particles are relieved, the polarization phenomenon of the weakened material in the charge and discharge process is reduced, and the direct current internal resistance of charge and discharge is reduced, so that under the requirement of meeting a certain specific energy density, the large-size graphite particles and the small-size graphite particles with different particle size distribution are mixed together, the coulomb efficiency of the silicon-based negative electrode can be improved, and the cycle stability and the low direct current internal resistance of charge and discharge are improved.
2) The composite negative electrode formed by mixing graphite particles and silicon particles with different particle size distributions is used for a lithium ion secondary battery, has the characteristics of high capacity, high coulomb efficiency, long cycle life, low charge-discharge direct current internal resistance and the like, and the smaller direct current internal resistance is a powerful basis for evaluating the safety of the battery besides better electrochemical performance of a reactive material.
Drawings
Fig. 1 is a schematic structural diagram of a silicon-graphite composite anode material of the present invention.
Wherein 100 is a silicon-graphite composite anode material, 110 large-size graphite particles, 120 small-size graphite particles and 130 silicon particles.
Detailed Description
The following examples will further illustrate the method provided by the present invention for a better understanding of the technical solution of the present invention, but the present invention is not limited to the examples listed but should also include any other known modifications within the scope of the claims of the present invention.
As shown in fig. 1, the silicon-graphite composite anode material 100 of the present invention comprises composite particles of silicon and graphite, wherein the graphite particles are composed of large-sized graphite particles 110 and small-sized graphite particles 120 having different particle size distributions, and a certain proportion of silicon particles 130 are uniformly dispersed in a graphite phase. The small-size graphite particles 120 and the silicon particles 130 are mixed in a relatively dense stacking manner, so that continuity of electron and ion transmission among the silicon particles is realized, and the small-size graphite particles can well play a role of a conductive network, so that the problem of poor conductivity of silicon is solved to a great extent.
However, if the simple mode of densely stacking silicon particles and small-size graphite particles is adopted, the requirement of the silicon on the stress required by the volume effect and the agglomeration effect caused by alloying/dealloying reaction cannot be met, the electrode still breaks and exposes more active area in the charging and discharging process, the SEI still can continuously passivate the continuously formed active surface, electrolyte is lost, and low coulombic efficiency is caused. According to the invention, researches show that a structure with a porous framework is formed by stacking large-size graphite particles with a certain proportion, so that sufficient stress requirements can be provided for alloying reaction of silicon, and the problem of poor electrode stability caused by volume effect and agglomeration effect is solved. However, if only large-sized graphite particles are used instead of small-sized graphite particles, it is difficult to achieve sufficient encapsulation of the silicon particles, and even excessive pore structure restricts the continuity of electron/ion transport between the silicon particles. The local small particles are uniformly wrapped, the structure of the whole large particles stably supported by the invention relieves the behaviors of poor conductivity, volume effect and mutual agglomeration of broken silicon particles, and the polarization phenomenon of the weakened material in the charge and discharge process reduces the direct current internal resistance of charge and discharge.
Therefore, under the requirement of meeting a certain specific energy density, the large-size and small-size graphite particles with different particle size distribution are mixed together, so that the coulomb efficiency of the silicon-based negative electrode can be improved, and the cycle stability and the lower direct current internal resistance of charge and discharge can be improved. The composite negative electrode formed by mixing graphite particles and silicon particles with different particle size distributions is used for a lithium ion secondary battery, and has the characteristics of high capacity, high coulomb efficiency, long cycle life, low charge-discharge direct current internal resistance and the like.
The invention relates to a silicon-graphite composite anode material, a lithium ion battery anode and a preparation process of the lithium ion battery, which concretely comprise the following steps:
s1, uniformly dispersing silicon particles in a graphite phase formed by graphite particles, wherein the silicon particles are Si and SiO 2 And SiO, preferably Si or SiO, the silicon particles having a particle diameter of 1 μm to 30 μm, preferably 1 μm to 10 μm, for example, the silicon particles having a D50 of 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or the like, but are not limited thereto.
S2. the graphite particles consist of two different particle size distributions of graphite particles having a D50 of from 1 μm to 100 μm, wherein the large size graphite particles D50 are from 20 μm to 100 μm, preferably from 30 μm to 70 μm and the small size graphite particles D50 are from 1 μm to 20 μm, preferably from 1 μm to 10 μm.
S3, the mass ratio of the silicon particles in the composite particles is 1% -50%, and preferably 3% -30%.
S4, the mass ratio of the graphite particles in the composite particles is 50% -99%, the mass ratio of the large-size graphite particles in the composite particles is preferably 40% -98.5%, and the mass ratio of the small-size graphite particles in the composite particles is preferably 0.5% -59%. The silicon-graphite composite anode material comprises the following components in percentage by mass based on the total mass of composite particles: 1 to 50 percent of silicon particles, 40 to 98.5 percent of large-size graphite particles and 0.5 to 59 percent of small-size graphite particles.
S5, the mixing method of the silicon particles and the graphite particles with the specific mass ratio adopts a mechanical and physical mixing mode, wherein the mechanical mode is preferably a mixing mode of a mixer, and can also be a mixing mode of a mechanical fusion machine, a ball mill, a high-speed mixer, a high-speed dispersing machine, a jet mill and the like, and the mixing mode is not particularly limited.
S6, after physical mixing, the prepared silicon-graphite composite material can be used for preparing a lithium ion battery negative electrode material, so as to prepare a lithium ion battery negative electrode, and further prepare a lithium ion battery.
The preparation of the lithium ion battery cathode comprises the steps of preparing slurry and coating, wherein the slurry is prepared by using one or more of water, methanol, ethanol, isopropanol, N-butanol, diethyl ether, acetone, N-methylpyrrolidone, benzene, toluene, xylene, N-dimethylformamide and chloroform, the binder is one or more of styrene-butadiene rubber emulsion, sodium hydroxymethyl cellulose, polyacrylic acid, polyacrylonitrile, polyacrylate and polyvinylidene fluoride, and the conductive agent is one or more of Super P, acetylene black, natural graphite, artificial graphite, ketjen black, carbon nanotubes, graphene, carbon fibers and fullerene.
The above-mentioned negative electrode of lithium ion battery and preparation method of lithium ion battery can refer to the prior art, this is well known to those skilled in the art, and the key of the present invention is the structural design of the negative electrode material.
The invention is further illustrated, but not limited, by the following examples.
The following reaction materials were used in the following examples and comparative examples:
silicon particles (trade name SA 99-SIO) used, shanghai Tewang photoelectric materials Co., ltd;
graphite grain used (trade mark AML 400), jiangsu purple, science and technology limited;
the thickener used was sodium hydroxymethyl cellulose (trade name CMC2200, manufactured by JECT Kogyo Co., ltd.);
the adhesive used was modified polyacrylic acid (modified PAA) (trademark ETERESM-BA1810, changxing Material industries, inc.;
the conductive agent used was conductive carbon black Super P (trademark ENSACO 250G), very dense high graphite Co., ltd.
The performance test method of the silicon-graphite composite anode material and the lithium ion battery prepared by the invention comprises the following steps:
a charge-discharge tester of Shenzhen Xinwei electronic Limited company is used for carrying out charge-discharge test and direct current internal resistance test, the voltage window is 0.01-1.50V, the current density is 0.05C, and the charge-discharge cycle is 50 circles.
Example 1:
5wt% silicon particles with D50 of 4.4 μm (containing Si, siO and SiO 2 ) Is mixed with 76wt% of large-size (d50=35.6 μm) graphite particles and 19wt% of small-size (d50=3.7 μm) graphite particles by a mixer, and the mass ratio of the large-size graphite particles to the small-size graphite particles is (8: 2) The three materials are fully mixed to obtain the active material.
The mass ratio of the active material, the binder and the conductive agent is 94:4:3, preparing slurry according to the proportion. CMC and modified PAA (the mass ratio of the CMC to the modified PAA is 2:3) are added into 5.316g of water, a binder solution is obtained through stirring, then 0.161g of super P is added into the binder solution, stirring and homogenizing are carried out for 2 minutes, and then 5g of active material is added, and stirring and homogenizing are carried out for 7 minutes. Finally, the silicon-graphite composite anode material is obtained.
And (3) coating the slurry on copper foil, drying, rolling and cutting to obtain the pole piece for testing the half battery. And stacking the pole piece, the diaphragm, the lithium piece, the stainless steel gasket and the elastic piece in sequence, dripping electrolyte into a 2032 button cell shell, and sealing to obtain the lithium ion half cell. Some column performance tests were performed using a charge-discharge tester.
The charge and discharge test conditions were as follows: discharge to 1.5V in constant current mode at 0.1C and charge to 0.001V in constant current/constant voltage mode.
Example 2:
10wt% silicon particles with D50 of 4.4 μm (containing Si, siO and SiO 2 ) Is mixed with 67.5wt% of large-size (d50=35.6 μm) graphite particles and 22.5wt% of small-size (d50=3.7 μm) graphite particles by a mixer, and the mass ratio of the large-size graphite particles is (75: 25 And (3) fully mixing the three materials to obtain the active material.
The remaining steps were the same as in example 1.
Example 3:
15wt% silicon particles with D50 of 4.4 μm (containing Si, siO andSiO 2 ) Is mixed with 59.5wt% of large-size (d50=35.6 μm) graphite particles and 25.5wt% of small-size (d50=3.7 μm) graphite particles by a mixer, and the mass ratio of the large-size graphite particles is (7: 3) The three materials are fully mixed to obtain the active material.
The remaining steps were the same as in example 1.
Example 4:
48wt% of silicon particles (containing Si, siO and SiO 2) with a D50 of 1.7 μm and 42wt% of large-size (D50=98.7 μm) graphite particles and 10wt% of small-size (D50=1.4 μm) graphite particles are mixed by a mixer, and the mass ratio of the large-size graphite particles to the small-size graphite particles is (81:19), and the active material is obtained after the three are fully mixed.
The remaining steps were the same as in example 1.
Example 5:
d50 is 28.9 μm of 3wt% silicon particles (containing Si, siO and SiO 2) and 96wt% of large-size (d50=23.2 μm) graphite particles and 1wt% of small-size (d50=4.4 μm) graphite particles are mixed by a mixer, and the mass ratio of the large-size graphite particles to the small-size graphite particles is (99:1), and the active material is obtained after the three are fully mixed.
Example 6:
25wt% silicon particles (containing Si, siO and SiO 2) having a D50 of 14.7 μm and 70wt% large-size (d50=63.2 μm) graphite particles and 5wt% small-size (d50=10.3 μm) graphite particles were mixed by a mixer, and the mass ratio of the large-size graphite particles to the small-size graphite particles was (93:7), and the three were thoroughly mixed to obtain an active material.
The remaining steps were the same as in example 1.
Example 7:
d50 is mixed by a mixer with 2wt% silicon particles (containing Si, siO and SiO 2) of 14.7 μm and 40wt% large-size (d50=63.2 μm) graphite particles and 58wt% small-size (d50=18.9 μm) graphite particles, and the mass ratio of the large-size graphite particles to the small-size graphite particles is (36:64), and the active material is obtained after the three are fully mixed.
Comparative example 1
5wt% silicon particles with D50 of 4.4 μm (containing Si, siO and SiO 2 ) To 95wt% of large-size (d50=35.6 μm) graphite particlesMixing with a mixer, and mixing to obtain active material.
The remaining steps were the same as in example 1.
Comparative example 2
5wt% silicon particles with D50 of 4.4 μm (containing Si, siO and SiO 2 ) And 95wt% of small-sized (d50=3.7 μm) graphite particles were mixed by a mixer, and the two were thoroughly mixed to obtain an active material.
The remaining steps were the same as in example 1.
Comparative example 3
10wt% silicon particles with D50 of 4.4 μm (containing Si, siO and SiO 2 ) Mixing with 90wt% of large-size (d50=35.6 μm) graphite particles by a mixer, and mixing the two sufficiently to obtain an active material.
The remaining steps were the same as in example 1.
Comparative example 4
10wt% silicon particles with D50 of 4.4 μm (containing Si, siO and SiO 2 ) And 90wt% of small-sized (d50=3.7 μm) graphite particles were mixed by a mixer, and the two were thoroughly mixed to obtain an active material.
The remaining steps were the same as in example 1.
Comparative example 5:
15wt% silicon particles with D50 of 4.4 μm (containing Si, siO and SiO 2 ) And 85wt% of large-sized (d50=35.6 μm) graphite particles were mixed by a mixer, and the two were thoroughly mixed to obtain an active material.
The remaining steps were the same as in example 1.
Comparative example 6:
15wt% silicon particles with D50 of 4.4 μm (containing Si, siO and SiO 2 ) And 85wt% of small-sized (d50=3.7 μm) graphite particles were mixed by a mixer, and the two were thoroughly mixed to obtain an active material.
The remaining steps were the same as in example 1.
Comparative example 7:
5wt% silicon particles with D50 of 4.4 μm (containing Si, siO and SiO 2 ) With 76wt% of graphite particles of a first size (d50=3.7 μm) and 19wt% of graphite particles of a second size (d50=1.6 μm) The graphite particles were mixed by a mixer, and the mass ratio of the large and small graphite particles was (8: 2) The three materials are fully mixed to obtain the active material.
The remaining steps were the same as in example 1.
Comparative example 8:
5wt% silicon particles with D50 of 4.4 μm (containing Si, siO and SiO 2 ) Is mixed with 76wt% of first size (d50=6.3 μm) graphite particles and 19wt% of second size (d50=3.7 μm) graphite particles by a mixer, and the mass ratio of the size graphite particles is (8: 2) The three materials are fully mixed to obtain the active material.
The remaining steps were the same as in example 1.
Comparative example 9:
5wt% silicon particles with D50 of 4.4 μm (containing Si, siO and SiO 2 ) Is mixed with 76wt% of first size (d50=14.2 μm) graphite particles and 19wt% of second size (d50=6.3 μm) graphite particles by a mixer, and the mass ratio of the size graphite particles is (8: 2) The three materials are fully mixed to obtain the active material.
The remaining steps were the same as in example 1.
The main process conditions and the prepared lithium ion half-cell performance test data of the examples and the comparative examples are shown in the following table 1:
table 1 main process conditions and battery performance data tables for examples and comparative examples
From the electrochemical data in the table, the size graphite particles co-blended silicon particle composite material is superior in charging capacity, coulombic efficiency and cycling stability to the single doped form using either the large size graphite particles alone or the small size graphite particles alone. In addition, as the prior art adopts two small-size graphite particles for blending, the charging capacity, the first efficiency and the 50-cycle retention rate of the obtained lithium ion battery are obviously inferior to those of the lithium ion battery prepared by the process of the embodiment of the invention. The composite negative electrode is used for a lithium ion secondary battery, has the characteristics of high capacity, high coulombic efficiency and long cycle life, and has good cycle stability.
DC polarization internal resistance (DCIR) test data of the lithium ion half batteries prepared in the examples and the comparative examples under different SOC conditions are shown in the following table 2:
TABLE 2 direct current internal polarization resistance (DCIR) data sheet under different SOC conditions
From DCIR under different SOCs, the charging DC internal resistance of the silicon particle composite material with the combined doping of the large and small graphite particles is smaller than that of the single doping form of the large and small graphite particles, the material has better electrochemical performance, and the material also has higher safety performance.
While the present invention has been described in detail through the foregoing description of the preferred embodiment, it should be understood that the foregoing description is not to be considered as limiting the invention. Those skilled in the art will appreciate that certain modifications and adaptations of the invention are possible and can be made under the teaching of the present specification. Such modifications and adaptations are intended to be within the scope of the present invention as defined in the appended claims.
Claims (9)
1. The silicon-graphite composite anode material comprises silicon particles and graphite particles, and is characterized in that the silicon particles are uniformly dispersed in a graphite phase consisting of the graphite particles to form composite particles; the graphite particles consist of two graphite particles with different particle size distributions, wherein the D50 of the graphite particles is 1-100 mu m, the large-size graphite particles have a particle size with the D50 of 30-100 mu m, and the small-size graphite particles have the D50 of 1-20 mu m;
the silicon particles have a particle diameter with a D50 of 1 μm to 30 μm;
the mass ratio of the silicon particles in the composite particles is 5% -50%, and the mass ratio of the graphite particles in the composite particles is 50% -95%;
wherein, the mass ratio of the large-size graphite particles in the composite particles is 40% -98.5%, and the mass ratio of the small-size graphite particles in the composite particles is 0.5% -59%.
2. The silicon-graphite composite anode material according to claim 1, wherein the large-sized graphite particles have a particle diameter of 30 μm to 70 μm in D50, the small-sized graphite particles have a particle diameter of 1 μm to 10 μm in D50, and the silicon particles have a particle diameter of 1 μm to 10 μm in D50.
3. The silicon-graphite composite anode material according to claim 1 or 2, wherein the silicon particles are Si, siO 2 And any one or more of SiO.
4. A method for preparing a silicon-graphite composite negative electrode material according to any one of claims 1 to 3, wherein the silicon particles and the graphite particles are mechanically mixed to obtain the silicon-graphite composite negative electrode material.
5. The method for preparing a silicon-graphite composite anode material according to claim 4, wherein the mechanical mixing mode is one or more selected from a mechanical fusion machine, a mixer, a ball mill, a high-speed mixer, a high-speed disperser and a jet mill.
6. A lithium ion battery, characterized in that the lithium ion battery anode is made of the silicon-graphite composite anode material according to any one of claims 1-3.
7. The lithium ion battery according to claim 6, wherein the dispersing agent used in the preparation process of the negative electrode of the lithium ion battery is any one or more selected from water, methanol, ethanol, isopropanol, N-butanol, diethyl ether, acetone, N-methylpyrrolidone, benzene, toluene, xylene, N-dimethylformamide and chloroform.
8. The lithium ion battery according to claim 6, wherein the binder used in the preparation process of the negative electrode of the lithium ion battery is any one or more selected from styrene-butadiene rubber emulsion, sodium hydroxymethyl cellulose, polyacrylic acid, polyacrylonitrile, polyacrylate and polyvinylidene fluoride.
9. The lithium ion battery according to claim 6, wherein the conductive agent used in the preparation process of the negative electrode of the lithium ion battery is any one or more selected from Super P, acetylene black, natural graphite, artificial graphite, ketjen black, carbon nanotubes, graphene, carbon fibers and fullerene.
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