CN112952048A - Silicon-carbon composite negative electrode material, preparation method thereof, electrode and secondary battery - Google Patents
Silicon-carbon composite negative electrode material, preparation method thereof, electrode and secondary battery Download PDFInfo
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Abstract
The invention belongs to the technical field of lithium ion batteries, and discloses a silicon-carbon composite negative electrode material, a preparation method thereof, an electrode and a secondary battery. The preparation method provided by the invention comprises the following steps: mixing and ball-milling conductive carbon and nano-silicon to obtain a silicon/carbon complex; mixing the silicon/carbon composite and the soft carbon to obtain a precursor; calcining the precursor in an inert gas atmosphere to obtain the silicon-carbon composite anode material with the core-shell structure; the weight percentage of the nano silicon is 2-20%, and the weight percentage of the soft carbon is 2-4% calculated by the total weight of the conductive carbon, the nano silicon and the soft carbon being 100%. The silicon-carbon composite negative electrode material prepared by the preparation method has a core-shell structure and comprises the following components: a silicon/carbon composite and a carbon layer coated on the surface of the silicon/carbon composite; in the silicon-carbon composite negative electrode material, the weight percentage of silicon is 2-20%, and the weight percentage of the carbon layer is 2-4%. The volume expansion effect of the silicon material is effectively relieved, and the silicon material has good cycle performance.
Description
Technical Field
The invention belongs to the technical field of lithium ion batteries, and particularly relates to a silicon-carbon composite negative electrode material and a preparation method thereof, and also relates to an electrode and a secondary battery.
Background
With the rapid development of the fields of new energy electric vehicles and industrial energy storage systems, the demand for lithium ion batteries with high energy density, high power density, long cycle life and the like is increasingly urgent. The negative electrode material directly affects performance indexes such as energy density, power density and cycle of the lithium ion battery, so that the synthesis and performance research of the high-capacity negative electrode material are widely concerned by researchers. At present, the traditional lithium ion battery negative electrode material is a graphite material (artificial graphite, natural graphite, mesocarbon microbeads and the like), but the requirement of the development trend of higher and higher energy density of the lithium ion battery cannot be met due to the lower specific capacity (the theoretical specific capacity is 372 mAh/g).
A great deal of current work is devoted to develop a novel negative electrode material with a higher specific capacity to replace the conventional graphite-type negative electrode material, and due to the higher storage capacity (theoretical specific capacity of 4200mAh/g), a higher voltage platform (about 0.4V) and abundant resources, silicon materials have attracted extensive attention of researchers, and are considered to be one of ideal candidate materials for developing a new-generation negative electrode material of a lithium ion battery with high specific energy and high power density. However, the silicon material is easy to have the problem of volume expansion in the circulation process, and can generate large volume expansion (up to 300%) in the charging process so as to cause pulverization of a silicon negative electrode, so that the silicon is not in contact with a current collector copper foil, and a new SEI film can be formed on a new silicon surface exposed in an electrolyte, so that the capacity of the silicon material is sharply reduced; further, silicon has a weak conductivity, and silicon as a semiconductor has a very low electron conductivity of only 6.7 × 10-4Scm-1These problemsPreventing the silicon cathode material from being widely applied to the lithium ion battery.
In view of the above-mentioned problems hindering the application and development of silicon cathodes, researchers have also proposed corresponding improved research methods, respectively. The main methods at present are: active or inactive materials with good conductivity and small volume effect are introduced into the silicon material to prepare the multiphase composite material, so that the volume effect of silicon is buffered, the conductivity of the material is enhanced, and the electrochemical performance of the silicon-based material is improved. According to the morphology and material structure of silicon, the existing silicon-carbon composite negative electrode material includes three types, such as a core-shell type, a porous type and a fiber type, for example, a silicon-carbon composite negative electrode material with a core-shell structure prepared by mechanical mixing or ball milling mixing and then thermal cracking, or a silicon-carbon composite negative electrode material obtained by coating a mesoporous silicon material with carbon.
CN103107315A discloses a nano silicon-carbon composite material and a preparation method thereof, which is characterized in that silicon dioxide is reduced to form a silicon-carbon composite material of carbon-carried nano silicon by a molten salt electrolysis method, wherein silicon and carbon are connected by nano silicon carbide, and the composite material is a metallurgical-grade combination. However, the material has poor conductivity due to the existence of silicon carbide, and the nano silicon is exposed in the electrolyte, so that lithium is continuously consumed by the silicon in the material in the circulation process, and the circulation performance is reduced.
CN102394287A discloses a silicon-carbon cathode material of a lithium ion battery and a preparation method thereof, which is characterized in that nano silicon slurry prepared by grinding is dried and granulated by a circulating drying powder preparation device, then carbon nano tubes and/or carbon nano fibers are deposited on the surfaces of the particles to form cores, and the surfaces of the cores are coated with organic cracking carbon layers. The size of secondary particles formed after the nano silicon is dried and granulated is in the micron order, and trace amount of cracking carbon exists among the nano silicon particles, so that the improvement on the powdering speed and the capacity retention rate of the material in the circulation process is facilitated. However, the nano silicon forms micron-sized secondary particles after granulation, a matrix with good buffer volume expansion does not exist among the nano silicon particles, the absolute expansion size of the material is still large in the circulation process, and the material still can be pulverized quickly after several cycles, so that the capacity is attenuated.
Although various preparation processes and routes of silicon-carbon composite negative electrode materials have been developed at present, the preparation processes and routes are complex in steps and high in cost, and the preparation processes and routes are not suitable for industrial production, and the electrochemical performance of batteries prepared from the existing silicon-carbon composite negative electrode materials still needs to be further improved.
Disclosure of Invention
The invention aims to solve the problem that the silicon-carbon composite cathode material prepared by the existing preparation process of the silicon-carbon composite cathode material has poor electrochemical performance.
In order to achieve the above object, in a first aspect, the present invention provides a method for preparing a silicon-carbon composite anode material, comprising the following steps:
mixing and ball-milling conductive carbon and nano-silicon to obtain a silicon/carbon complex;
mixing the silicon/carbon composite and the soft carbon to obtain a precursor;
calcining the precursor in an inert gas atmosphere to obtain the silicon-carbon composite anode material with the core-shell structure;
wherein, the weight percentage of the nano silicon is 2-20%, and the weight percentage of the soft carbon is 2-4%, based on the total weight of the conductive carbon, the nano silicon and the soft carbon being 100%.
The preparation method of the silicon-carbon composite negative electrode material provided by the invention has the following advantages:
according to the preparation method of the silicon-carbon composite negative electrode material, on one hand, the conductive carbon and the nano silicon are mixed and ball-milled, so that the nano silicon can be uniformly embedded in a structure of the conductive carbon in the mixing process, the conductive carbon is used as a buffer matrix for volume expansion in the silicon charging and discharging process, the volume expansion effect of a silicon material is effectively relieved, the addition of the conductive carbon is beneficial to improving the diffusion speed of lithium ions and electrons in the material, and the conductivity of the silicon material is effectively improved; on the other hand, the silicon/carbon composite and the soft carbon are mixed to uniformly disperse the silicon/carbon composite in the soft carbon to form a soft carbon pre-coated composite microsphere, and then the soft carbon coated with the silicon/carbon composite is carbonized through calcination and crushing to form a silicon-carbon composite anode material which takes the silicon/carbon composite as a core and takes a carbon layer as a shell layer, the coating of the carbon layer improves the structural integrity of the electrode material, further relieves the volume expansion effect of the silicon material, and simultaneously provides good electronic and ion channels for the material, thereby remarkably improving the performance stability of the silicon-carbon composite anode material in the charge-discharge cycle process; in another aspect, the invention adjusts the amount of the raw material nano silicon to be 2 wt% -20 wt% and the amount of the raw material soft carbon to be 2 wt% -4 wt%, so that the silicon-carbon composite negative electrode material prepared by the method has excellent performance, and the battery prepared by the silicon-carbon composite negative electrode material has excellent electrochemical properties such as charge-discharge efficiency, direct current internal resistance, circulation and the like.
Compared with the prior art, the preparation method of the silicon-carbon composite anode material provided by the invention does not need to use a surfactant or a corrosive acid-base reagent, does not need precise reaction time control and a complex preparation flow, and is simple, convenient and controllable in process and environment-friendly; meanwhile, by introducing conductive carbon to prepare a silicon/carbon complex, coating the silicon/carbon complex by adopting a carbon layer and adjusting the consumption of the raw materials of nano silicon and soft carbon, the volume expansion effect of the silicon material is effectively relieved, the electrochemical performance of the silicon-carbon composite cathode material is endowed, and the charge-discharge capacity and the cycle performance of the material are effectively improved.
In one embodiment, in the step of calcining the precursor, the precursor is calcined at 700-1000 ℃.
In one embodiment, the conductive carbon is selected from at least one of graphite, carbon black, coke, mesocarbon microbeads, carbon fibers, and carbon nanotubes.
In one embodiment, the soft carbon is selected from pitch.
In one embodiment, the nano silicon has a particle size of 20nm to 50 nm.
In one embodiment, in the step of performing mixing ball milling on the conductive carbon and the nano silicon, the rotation speed of the mixing ball milling is 250rpm-300rpm, and the ball-to-material ratio is (10-15): 1.
In one embodiment, after the step of calcining the precursor, the method further comprises: and crushing the calcined product until the particle size of the material is less than 30 mu m.
In a second aspect, the invention provides a silicon-carbon composite negative electrode material, which is prepared by the above preparation method, and the silicon-carbon composite negative electrode material has a core-shell structure, and comprises: a silicon/carbon composite and a carbon layer coated on the surface of the silicon/carbon composite;
in the silicon-carbon composite negative electrode material, the weight percentage of silicon is 2-20%, and the weight percentage of a carbon layer is 2-4%.
The silicon-carbon composite negative electrode material provided by the invention is prepared by the method, has a core-shell structure, and comprises the following components: the silicon/carbon composite and the carbon layer coated and arranged on the surface of the silicon/carbon composite are introduced, the carbon material in the silicon/carbon composite is coated and modified with the carbon layer on the surface of the silicon/carbon composite, the volume expansion effect of the silicon material is effectively relieved, the cycle performance of the electrode material is improved, good electronic and ion channels are provided for the material, and the silicon-carbon composite cathode material is endowed with good electrochemical stability.
In a third aspect, the present invention provides an electrode comprising: the silicon-carbon composite negative electrode material prepared by the preparation method or the silicon-carbon composite negative electrode material.
The electrode provided by the invention comprises the silicon-carbon composite negative electrode material, has a small volume expansion effect, has a complete and stable structure in the charge-discharge cycle process, has good conductivity, and can remarkably improve the electrochemical performance of a battery.
In a fourth aspect, the present invention provides a secondary battery comprising: the above-mentioned electrode.
The present invention provides a secondary battery comprising: the electrode comprises the silicon-carbon composite negative electrode material, is stable in structure, and has excellent electrochemical properties such as charge-discharge efficiency, direct-current internal resistance and circulation.
Drawings
FIG. 1 is an SEM image of silicon-carbon composite negative electrode materials A-D in test example 1 of the present invention;
FIG. 2 is an XRD spectrum of silicon-carbon composite anode materials A-D in test example 1 of the present invention;
FIG. 3 is a TG curve of Si-C composite anode materials A-D in test example 1 of the present invention;
fig. 4 shows the discharge curves of the soft-packed lithium ion batteries a to D at 20 ℃ and-20 ℃ in test example 2 of the present invention.
Detailed Description
In order to make the technical problems, technical solutions and advantageous effects to be solved by the present invention more clearly apparent, the present invention is further described in detail below with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
A preparation method of a silicon-carbon composite negative electrode material comprises the following steps:
s01, mixing and ball-milling the conductive carbon and the nano silicon to obtain a silicon/carbon complex;
s02, mixing the silicon/carbon composite and the soft carbon to obtain a precursor;
s03, calcining the precursor in an inert gas atmosphere to obtain the silicon-carbon composite anode material with the core-shell structure;
wherein, the weight percentage of the nano silicon is 2-20%, and the weight percentage of the soft carbon is 2-4%, based on the total weight of the conductive carbon, the nano silicon and the soft carbon being 100%.
According to the preparation method of the silicon-carbon composite negative electrode material provided by the embodiment of the invention, on one hand, the conductive carbon and the nano silicon are subjected to mixing ball milling, so that the nano silicon can be uniformly embedded in a structure of the conductive carbon in a mixing process, the conductive carbon is used as a buffer matrix for volume expansion in a silicon charging and discharging process, the volume expansion effect of a silicon material is effectively relieved, the addition of the conductive carbon is favorable for improving the diffusion speed of lithium ions and electrons in the material, and the conductivity of the silicon material is effectively improved; on the other hand, the silicon/carbon composite and the soft carbon are mixed to uniformly disperse the silicon/carbon composite in the soft carbon to form a soft carbon pre-coated composite microsphere, and then the soft carbon coated with the silicon/carbon composite is carbonized through calcination and crushing to form a silicon-carbon composite anode material which takes the silicon/carbon composite as a core and takes a carbon layer as a shell layer, the coating of the carbon layer improves the structural integrity of the electrode material, further relieves the volume expansion effect of the silicon material, and simultaneously provides good electronic and ion channels for the material, thereby remarkably improving the performance stability of the silicon-carbon composite anode material in the charge-discharge cycle process; in another aspect, the invention adjusts the amount of the raw material nano silicon to be 2 wt% -20 wt% and the amount of the raw material soft carbon to be 2 wt% -4 wt%, so that the silicon-carbon composite negative electrode material prepared by the method has excellent performance, and the battery prepared by the silicon-carbon composite negative electrode material has excellent electrochemical properties such as charge-discharge efficiency, direct current internal resistance, circulation and the like.
In the embodiment of the invention, the raw materials for preparing the silicon-carbon composite negative electrode material comprise conductive carbon, nano silicon and soft carbon, wherein the weight percentage of the nano silicon is 2-20%, the weight percentage of the soft carbon is 2-4% and the balance of the conductive carbon is 100% of the total weight of the conductive carbon, the nano silicon and the soft carbon. Accordingly, the silicon content of the silicon-carbon composite negative electrode material prepared by the raw material formula is 2% -20%, and in specific embodiments, the silicon content of the prepared silicon-carbon composite negative electrode material is 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%. Through tests, the embodiment of the invention adjusts the dosage of the raw materials to be in the range, so that the prepared silicon-carbon composite negative electrode material has excellent performance, and the battery prepared from the silicon-carbon composite negative electrode material has excellent electrochemical properties such as charge-discharge efficiency, direct-current internal resistance and circulation. In some test examples, the first discharge capacity and the first charge capacity of the battery prepared from the composite material are respectively up to 560.1mAh/g and 500.1mAh/g, the first coulombic efficiency is up to 92.6%, and the capacity retention rate reaches 77.7% after 300 cycles.
Specifically, in step S01, the conductive carbon and the nano-silicon are mixed and ball-milled to obtain a silicon/carbon composite.
According to the embodiment of the invention, the conductive carbon and the nano silicon are subjected to mixing ball milling, so that the nano silicon can be uniformly embedded in the structure of the conductive carbon in the mixing process, the conductive carbon is used as a buffer matrix for volume expansion in the silicon charging and discharging processes, the volume expansion effect of the silicon material is effectively relieved, the addition of the conductive carbon is beneficial to improving the diffusion speed of lithium ions and electrons in the material, and the conductivity of the silicon material is effectively improved.
The conductive carbon is a carbon material capable of conducting electricity, is used as a carbon matrix preparation raw material in a subsequently formed silicon/carbon complex, and provides good electron and ion channels while buffering volume expansion of silicon in the charge-discharge process, so that the performance stability of the negative electrode material in the charge-discharge cycle process is ensured. In one embodiment, the conductive carbon is selected from at least one of graphite, carbon black, ketjen black, Vapor Grown Carbon Fiber (VGCF), coke, mesocarbon microbeads (MCMB), carbon fibers, and carbon nanotubes. In some embodiments, the conductive carbon is selected from graphite, and the graphite has a pore structure, so that the nano silicon can be embedded into the graphite in a ball milling process, and can be used as a buffer matrix for volume expansion in a silicon charging and discharging process, and the volume effect of the silicon material can be favorably relieved. In some embodiments, the graphite has a particle size of 3.4 μm to 3.5 μm; in some embodiments, the carbon black has a particle size of 40 μm; in some embodiments, the ketjen black has a particle size of 30 to 50 μm; in some embodiments, the carbon nanotubes have a particle size of 5 μm; in some embodiments, the VGCF has a particle size of 150 μm.
The nano silicon can be selected from silicon materials conventional in the art, in some embodiments, the particle size of the nano silicon is 20nm-50nm, preferably 25nm-45nm, 30nm-40nm, and 35nm-50nm, the nano silicon in the size range has a shorter lithium ion transmission distance and a larger contact area, the high capacity of the silicon can be fully exerted, and the absolute volume change effect of the nano silicon in the charging and discharging process can be reduced to a certain extent. In some embodiments, the purity of the nano silicon is more than 99.9%, the higher the purity of the nano silicon is, the fewer impurities are, and when the silicon-carbon composite negative electrode material is applied to the preparation of an electrode, the fewer side reactions of other substances in a battery system are, which is beneficial to improving the conversion efficiency of a secondary battery prepared from the silicon-carbon composite negative electrode material.
And mixing and ball-milling the conductive carbon and the nano silicon, so that the nano silicon can be uniformly embedded in the structure of the conductive carbon in the mixing process.
In one embodiment, in the step of performing mixed ball milling on the conductive carbon and the nano silicon, the rotation speed of the mixed ball milling is 250rpm-300rpm, and the ball-to-material ratio is (10-15): 1. By optimizing the process of the mixing ball milling, the nano silicon and the conductive carbon are fully and uniformly mixed, the nano silicon is promoted to be uniformly embedded in the structure of the conductive carbon, and the volume expansion effect of the silicon material is further relieved. In some embodiments, the rotational speed of the mixing ball mill is 250rpm, 256rpm, 260rpm, 265rpm, 270rpm, 273rpm, 280rpm, 285rpm, 290rpm, 300 rpm. In some embodiments, the ball-to-feed ratio of the hybrid ball mill is 10:1, 11:1, 12:1, 13:1, 14:1, 15: 1. In some embodiments, the mixing and ball milling time is 1-2 hours.
In step S02, the silicon/carbon composite and the soft carbon are mixed to obtain a precursor.
According to the embodiment of the invention, the silicon/carbon composite and the soft carbon are mixed, so that the silicon/carbon composite is uniformly dispersed in the soft carbon to form the soft carbon pre-coated composite microsphere.
The soft carbon is used for pre-coating a subsequently formed silicon/carbon composite and can be graphitized by high-temperature calcination to form a carbon layer. As an embodiment, the soft carbon is selected from at least one of pitch, petroleum coke, needle coke, carbon fiber, and carbon microspheres. In some embodiments, the soft carbon is selected from asphalt, the asphalt is formed by deoxidizing and dehydrogenating petroleum asphalt through heat treatment at about 1000 ℃, and the asphalt is rich in resources and low in price. Compared to other soft carbon materials such as petroleum coke, pitch does not result in high lithium potential and thus does not limit battery capacity and energy density.
And mixing the silicon/carbon composite and the soft carbon to uniformly mix the components. In some embodiments, the silicon/carbon composite and the soft carbon are mixed in a mixer.
In step S03, calcining the precursor in an inert gas atmosphere to obtain a silicon-carbon composite anode material with a core-shell structure.
The precursor is calcined in an inert gas atmosphere to carbonize the soft carbon coating the silicon/carbon composite, thereby forming the silicon-carbon composite anode material with the silicon/carbon composite as a core and the carbon layer as a shell. On one hand, the carbon layer coating the silicon/carbon composite has certain mechanical strength, so that the silicon/carbon composite is tightly combined, the expansion of silicon in circulation is effectively inhibited, the structural integrity of the electrode material in the circulation process is ensured, and the circulation performance of the electrode material is improved. On the other hand, the coated carbon layer has a faster bulk phase lithium ion diffusion rate and good electrolyte compatibility, ensures good electrical contact among nanotube particles, improves the diffusion speed of lithium ions and electrons in the material, and enables a battery prepared from the silicon-carbon composite negative electrode material to have good electrochemical properties, such as high charge-discharge efficiency, small direct current internal resistance, stable circulation and the like.
In one embodiment, in the step of calcining the precursor, the precursor is calcined at 700 ℃ to 1000 ℃. The precursor is calcined at a high temperature of 700-1000 ℃ to soften and carbonize the pitch, so that a carbon layer is uniformly coated on the surface of the silicon/carbon composite to form the silicon-carbon composite anode material with the core-shell structure. When the calcining temperature is lower than 700 ℃, the phase transition temperature of the asphalt cannot be increased; when the calcination temperature is more than 1000 deg.c, a desired coating effect cannot be achieved. In some embodiments, the precursor is calcined at 700 ℃ to 1000 ℃ for 2 to 4 hours. In some embodiments, the precursor is calcined at 700 ℃, 790 ℃, 850 ℃, 910 ℃, 1000 ℃.
As an embodiment, after the step of calcining the precursor, the method further comprises: and (3) crushing the calcined product until the particle size of the material is smaller than 30 mu m, wherein the smaller the particle size of the material is, the more sufficient the prepared slurry is dispersed, so that the coating is more exquisite and uniform, and the densification degree of the electrode is favorably improved. In some embodiments, the size reduction process is performed using a jaw crusher.
Compared with the prior art, the preparation method of the silicon-carbon composite anode material provided by the embodiment of the invention does not need to use a surfactant or a corrosive acid-base reagent, does not need precise reaction time control and a complex preparation flow, and has simple, convenient and controllable process and environmental friendliness; meanwhile, by introducing conductive carbon to prepare a silicon/carbon complex, coating the silicon/carbon complex by adopting a carbon layer and adjusting the consumption of the raw materials of nano silicon and soft carbon, the volume expansion effect of the silicon material is effectively relieved, the electrochemical performance of the silicon-carbon composite cathode material is endowed, and the charge-discharge capacity and the cycle performance of the material are effectively improved.
Based on the technical scheme, the embodiment of the invention also provides the silicon-carbon composite anode material prepared by the preparation method, an electrode and a secondary battery.
Correspondingly, the silicon-carbon composite negative electrode material is prepared by the preparation method, has a core-shell structure and comprises the following components: a silicon/carbon composite and a carbon layer coated on the surface of the silicon/carbon composite;
in the silicon-carbon composite negative electrode material, the weight percentage of silicon is 2-20%, and the weight percentage of a carbon layer is 2-4%.
The silicon-carbon composite negative electrode material provided by the embodiment of the invention is prepared by the method, has a core-shell structure, and comprises the following components: the silicon/carbon composite material comprises a silicon/carbon composite body and a carbon layer coated and arranged on the surface of the silicon/carbon composite body, wherein the carbon layer is introduced into the silicon/carbon composite body and coated and modified on the surface of the silicon/carbon composite body, so that the volume expansion effect of the silicon material is effectively relieved, the structural integrity of the electrode material is kept, good electronic and ion channels are provided for the material, and the silicon/carbon composite anode material is endowed with good electrochemical stability.
In one embodiment, the silicon content of the silicon-carbon composite negative electrode material is 2% to 20% by weight.
In one embodiment, the particle size of the silicon-carbon composite negative electrode material is less than 30 μm.
Accordingly, an electrode, comprising: the silicon-carbon composite negative electrode material prepared by the preparation method or the silicon-carbon composite negative electrode material.
The electrode provided by the embodiment of the invention comprises the silicon-carbon composite negative electrode material, has a small volume expansion effect, has a complete and stable structure in the charge-discharge cycle process, has good conductivity, and can remarkably improve the electrochemical performance of a battery.
As an embodiment, the electrode includes: the current collector and coat in the material layer of current collector top, wherein, the material layer is formed by above-mentioned silicon carbon composite negative electrode material, conductive agent, binder mixture solidification. In some embodiments, the current collector is selected from copper foil or aluminum foil; in some embodiments, the conductive agent is selected from carbon black; in some embodiments, the binder is selected from at least one of polyvinyl alcohol, polytetrafluoroethylene, sodium carboxymethylcellulose (CMC), and Styrene Butadiene Rubber (SBR). During preparation, slurry containing the silicon-carbon composite negative electrode material, a conductive agent and a binder is coated on the surface of a current collector and is solidified to obtain the electrode.
Accordingly, a secondary battery includes: the above-mentioned electrode.
The embodiment of the invention provides a secondary battery, which comprises: the electrode comprises the silicon-carbon composite negative electrode material, is stable in structure, and has excellent electrochemical properties such as charge-discharge efficiency, direct-current internal resistance and circulation.
The secondary battery includes, but is not limited to, a lithium ion battery, a sodium ion battery, a magnesium ion battery, or the like. In some embodiments, the secondary battery is a lithium ion battery.
In order to make the above implementation details and operations of the present invention clearly understood by those skilled in the art, and to make the progress of the silicon-carbon composite anode material, the preparation method thereof, the electrode and the secondary battery apparent, the implementation of the present invention is illustrated by the following examples.
Example 1
The embodiment provides a silicon-carbon composite anode material, and a preparation method of the silicon-carbon composite anode material comprises the following steps:
(1) weighing 2 parts of nano silicon, 2 parts of asphalt and 96 parts of artificial graphite (produced by sequoia shanghai with specification of FS-1); the purity of the nano silicon is 99.9 percent, and the particle size is 20 nm;
(2) adding nano silicon into graphite, mixing uniformly, ball-milling in a planetary ball mill (marine products, specification PM-2A), setting the ball-milling rotation speed to be 250rmp, ball-milling time to be 1.5h, ball-milling material ratio to be 12:1, and obtaining a silicon/carbon complex;
(3) placing the silicon/carbon complex in a VC mixer (marine products, specification V150), adding asphalt, and mixing until the mixture is uniformly mixed to obtain a precursor;
(4) calcining the precursor in a high-temperature furnace (seafood, SG1400) at 850 ℃ for 2h in a nitrogen atmosphere, naturally cooling the material, taking out, crushing by using a jaw crusher, and sieving to obtain the silicon-carbon composite anode material with the core-shell structure, wherein the silicon content is 2 wt%.
The method for assembling and preparing the soft package lithium ion battery by taking the silicon-carbon composite negative electrode material prepared in the steps as a negative electrode active material specifically comprises the following steps:
1) pulping, coating and drying a negative active material, a conductive agent carbon black (Super P), CMC and SBR according to a mass ratio of 96: 1: 2 to obtain a negative pole piece;
2) preparing NCM, conductive agent carbon black (Super P) and PVDF into slurry according to the mass ratio of 98: 0.5: 1.5, coating, drying and rolling to obtain a positive pole piece;
3) and (3) preparing the positive plate, the negative plate and the diaphragm into a soft package lithium ion battery with the length of 110mm, the width of 80mm and the thickness of 5mm by a lamination process, injecting electrolyte after vacuum drying for 24h, standing for 12h, and preparing the soft package lithium ion battery, wherein the mark is A.
The differences between example 2-example 20 and comparative examples 1-5 from example 1 are shown in table 1.
TABLE 1
Comparative example 5
The comparative example prepares a soft package lithium ion battery e, and the preparation method is different from that of the example 1 in that: selecting graphite as a negative active material; the rest of the process is basically the same as that of embodiment 1, and the description thereof is omitted.
Test example 1
The silicon-carbon composite negative electrode materials prepared in examples 1 to 4 were used as test samples, respectively labeled A, B, C, D, and structural characterization of the materials was performed.
1. The appearance of the sample is observed by a FEI Quanta-200 type field emission Scanning Electron Microscope (SEM), the voltage is 5kV, and the surface of the sample is tested to spray gold.
2. The material was subjected to crystal structure analysis using an X-ray diffractometer (D/max-250, manufactured by Japan), copper target Ka radiation, wavelength 0.153nm, tube voltage 40kV, tube current 250mA, diffraction angle scanning range 10-80 DEG, and scanning speed 8 DEG/min.
3. The samples were studied in air using a thermogravimetric analyzer (TG, Netzsch STA 449C) with a temperature rise rate of 10 ℃/min. The specific surface area data of the material was measured using a Micromeritics Ins ASAP 2010M + C specific surface tester.
Fig. 1 is an SEM image of the silicon-carbon composite negative electrode material A, B, C, D, which shows that the silicon-carbon composite negative electrode material A, B, C, D has a substantially similar morphology, the material structure is an irregular block-like stacked structure, the particle size range of the material is 10-30 μm, the surface is smooth, and no silicon ball is exposed, indicating that the nano-silicon particle is completely coated with the carbon material.
Fig. 2 is an XRD spectrum of the silicon-carbon composite negative electrode material A, B, C, D, in which strong diffraction peaks appear at the positions of 2 θ of 26.5 °, 44.5 ° and 54.5 °, and correspond to the crystal planes (002), (101) and (004) of graphite. Three relatively weak diffraction characteristic peaks and curve peaks appearing at 28.4 degrees, 47.3 degrees and 56.1 degrees respectively correspond to crystal faces (111), (220) and (311) of silicon, and the silicon-carbon composite anode material prepared by the embodiment of the invention is composed of graphite and silicon and keeps a good crystal structure.
Fig. 3 is a thermogravimetric analysis curve (TG curve) of the silicon-carbon composite anode material A, B, C, D, and it can be seen from the graph that the material has an obvious weight loss behavior from 650 ℃, because the carbon material in the silicon-carbon material starts to be pyrolyzed, the weight loss reaches the lowest at 1150 ℃, and the graphite and the soft carbon material are pyrolyzed completely; the curve then shows a tendency to rise with temperature, since silicon starts to oxidize at high temperatures to form SiOXAnd the mass is increased. Since the composition of the silicon carbon composite anode material A, B, C, D is both silicon and carbon, the thermogravimetric curve trend remains substantially consistent.
Test example 2
The following electrochemical performance tests were carried out using the Ningbo Baote test system (specification NBT-32T, Ningbo product) on the soft-packed lithium ion batteries A-T obtained in examples 1-20 and the soft-packed lithium ion batteries a-e obtained in comparative examples 1-5:
(1) the charge-discharge curve test of the battery shows that the current is 1C, the charge cut-off voltage is 4.2V, the room-temperature discharge cut-off voltage is 2.75V, and the discharge cut-off voltage at the temperature of minus 20 ℃ is 2.2V;
(2) the battery is subjected to cycle test, wherein the charging and discharging current is 1C, the charging cut-off voltage is 4.20V, the discharging cut-off voltage is 2.75V, the cut-off voltage is 2.2V at minus 20 ℃, and the test environment temperature is 20 ℃.
Fig. 4 is a discharge curve of the soft package lithium ion batteries a to D at 20 ℃ and a discharge curve at-20 ℃, and as shown in the figure, as the content of silicon in the negative electrode material increases, the voltage plateau and the capacity retention rate of the batteries during low-temperature discharge gradually increase. The soft package lithium ion battery A has the capacity at the normal temperature of 3.45Ah at the temperature of 20 ℃, the capacity at the low temperature of-20 ℃ of 2.35Ah, and the capacity retention rate at the low temperature of 68.1 percent; the soft package lithium ion battery B has a normal temperature capacity at 20 ℃ of 3.44Ah, a low temperature capacity at 20 ℃ of 2.73Ah and a capacity retention rate at low temperature of 72.4%; the soft package lithium ion battery C has a normal temperature capacity at 20 ℃ of 3.43Ah, a low temperature capacity at 20 ℃ of 2.68Ah and a capacity retention rate at low temperature of 78.1%; the soft package lithium ion battery D has a normal temperature capacity at 20 ℃ of 3.44Ah, a low temperature capacity at 20 ℃ of 2.79Ah and a capacity retention rate at low temperature of 81.1%. In summary, it is shown that the soft package lithium ion battery provided by the embodiment of the present invention has a small polarization in a discharge state, so that the discharge voltage plateau of the soft package lithium ion battery is slightly high, and thus the capacity retention rate of the soft package lithium ion battery at low temperature is also good.
Table 2 shows the capacity retention rates of the soft-package lithium ion batteries a to T and the soft-package lithium ion batteries a to e prepared in comparative examples 1 to 5 after being subjected to 1C charge-discharge cycle for 300 times, as shown by the results, the capacity retention rates of the soft-package lithium ion batteries a to T after being subjected to 300 cycles are all greater than those of the soft-package lithium ion batteries a to e, and the capacity retention rates reflect the cycle performance of the batteries, which indicates that the soft-package lithium ion batteries provided by the embodiment of the present invention have good cycle stability.
Compared with soft package lithium ion batteries a-e, the negative electrode material of the soft package lithium ion batteries A-T has the raw materials of 2-20 wt% of nano silicon and 2-4 wt% of soft carbon, which shows that the cycle performance of the lithium ion batteries can be effectively improved by adjusting the use amounts of the raw materials of the negative electrode material of the nano silicon and the soft carbon within the above ranges.
TABLE 2
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.
Claims (10)
1. The preparation method of the silicon-carbon composite negative electrode material is characterized by comprising the following steps of:
mixing and ball-milling conductive carbon and nano-silicon to obtain a silicon/carbon complex;
mixing the silicon/carbon composite and the soft carbon to obtain a precursor;
calcining the precursor in an inert gas atmosphere to obtain the silicon-carbon composite anode material with the core-shell structure;
wherein, the weight percentage of the nano silicon is 2-20%, and the weight percentage of the soft carbon is 2-4%, based on the total weight of the conductive carbon, the nano silicon and the soft carbon being 100%.
2. The production method as claimed in claim 1, wherein in the step of calcining the precursor, the precursor is calcined at 700-1000 ℃.
3. The method according to claim 1, wherein the conductive carbon is at least one selected from graphite, carbon black, ketjen black, vapor-grown carbon fiber, coke, mesocarbon microbeads, carbon fiber, and carbon nanotubes.
4. The method of claim 1, wherein the soft carbon is selected from at least one of pitch, petroleum coke, needle coke, carbon fiber, and carbon microspheres.
5. The method according to claim 1, wherein the nano silicon has a particle size of 20nm to 50 nm.
6. The preparation method according to any one of claims 1 to 5, wherein in the step of subjecting the conductive carbon and the nano-silicon to mixed ball milling, the rotation speed of the mixed ball milling is 250rpm to 300rpm, and the ball-to-material ratio is (10-15): 1.
7. The production method according to any one of claims 1 to 5, characterized by further comprising, after the step of calcining the precursor: and crushing the calcined product until the particle size of the material is less than 30 mu m.
8. The silicon-carbon composite negative electrode material is characterized by having a core-shell structure and comprising: a silicon/carbon composite and a carbon layer coated on the surface of the silicon/carbon composite;
in the silicon-carbon composite negative electrode material, the weight percentage of silicon is 2-20%, and the weight percentage of a carbon layer is 2-4%.
9. An electrode, comprising: the silicon-carbon composite anode material produced by the production method according to any one of claims 1 to 7, or the silicon-carbon composite anode material according to claim 8.
10. A secondary battery, characterized by comprising: the electrode of claim 9.
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| CN114975934A (en) * | 2022-06-02 | 2022-08-30 | 鞍钢集团北京研究院有限公司 | Silicon-carbon composite material and preparation method and application thereof |
| CN115020666A (en) * | 2022-06-21 | 2022-09-06 | 鞍钢集团北京研究院有限公司 | Preparation method of silicon-carbon composite negative electrode material |
| CN116072872A (en) * | 2022-12-27 | 2023-05-05 | 重庆太蓝新能源有限公司 | Silicon-carbon negative electrode material, preparation method thereof and lithium ion battery |
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