CN111370650A - Amorphous silicon-graphite composite material and preparation method and application thereof - Google Patents
Amorphous silicon-graphite composite material and preparation method and application thereof Download PDFInfo
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Abstract
The invention belongs to the technical field of composite materials, and particularly relates to an amorphous silicon-graphite composite material as well as a preparation method and application thereof. The amorphous silicon-graphite composite material provided by the invention comprises a current collector, a graphite conducting layer and an amorphous silicon deposition layer which are sequentially stacked. The graphite conducting layer in the amorphous silicon-graphite composite material can contain partial silicon material, plays a role in buffering silicon expansion, and is favorable for improving the cycle stability of the composite material; the amorphous silicon is beneficial to reducing the structural strain force of the composite material, further reducing the volume change of the composite material, and further being beneficial to improving the cycle stability and the rate capability of the amorphous silicon-graphite composite material. The test result of the embodiment shows that the amorphous silicon-graphite composite material provided by the invention still has the capacity of 1100mAh/g after being cycled for 50 times, and has good cycling stability and excellent rate performance.
Description
Technical Field
The invention belongs to the technical field of electrode materials, and particularly relates to an amorphous silicon-graphite composite material as well as a preparation method and application thereof.
Background
A lithium ion battery is a secondary battery (rechargeable battery) that mainly operates by movement of lithium ions between a positive electrode and a negative electrode, during charging and discharging, Li+Intercalation and deintercalation to and from two electrodes: upon charging, Li+The lithium ion battery is extracted from the positive electrode and is inserted into the negative electrode through the electrolyte, and the negative electrode is in a lithium-rich state; the opposite is true during discharge. Lithium ion batteries find great application in the field of energy storage due to their high energy density and high power output. Silicon is one of the candidates of a plurality of negative electrode materials of the lithium ion battery, and the theoretical specific capacity at normal temperature is 3572 mAh.g-1Much higher than that of graphite (372mAh g)-1) The material is a known lithium ion battery negative electrode material with the highest specific capacity; besides, it has the advantages of low charge-discharge potential, low price, environmental protection and the like. However, in the process of charging and discharging pure silicon, because lithium ions are continuously alloyed and dealloyed with silicon, a huge volume expansion effect (up to 300%) of silicon is caused, which can lead to the crushing and pulverization of silicon cathode materials, cause the silicon cathode materials to fall off from a current collector, cause the rapid reduction of battery capacity, and seriously limit the practical application of silicon in lithium ion batteries.
In order to enable the silicon negative electrode material to maintain high cycling stability, at present, there are two main types of modification of the silicon material. One is to improve the material itself, such as changing the crystal form, shape and size of the material itself, such as nano-crystallizing the silicon material; the other is to achieve the effect of well controlling the volume expansion by using a composite silicon system with a special structure, for example, a carbon material and silicon form a porous structure composite, although the stability of the material is improved to a certain extent, the irreversible capacity is very large during the first charge and discharge, and the practical application of the composite silicon is limited.
Disclosure of Invention
In view of the above, the present invention aims to provide an amorphous silicon-graphite composite material, which has good cycling stability and excellent rate capability, and effectively improves the volume expansion problem of a silicon negative electrode material; the invention also provides a preparation method and application of the amorphous silicon-graphite composite material.
In order to achieve the purpose of the invention, the invention provides the following technical scheme:
the invention provides an amorphous silicon-graphite composite material which comprises a current collector, a graphite conducting layer and an amorphous silicon deposition layer which are sequentially stacked.
The invention also provides a preparation method of the amorphous silicon-graphite composite material in the technical scheme, which comprises the following steps:
mixing graphite, a conductive agent, a binder and an organic solvent to obtain slurry;
after the slurry is coated on a current collector, sequentially carrying out air blast drying and vacuum drying to obtain a current collector-graphite layer material;
and (3) carrying out constant potential electrodeposition in a silicon-containing electrodeposition solution by using the current collector-graphite layer material as a working electrode by using a three-electrode system, and depositing on the surface of the graphite layer of the current collector-graphite layer material to obtain amorphous silicon so as to obtain the amorphous silicon-graphite composite material.
Preferably, the mass ratio of the graphite to the conductive agent to the binder is (7-8): (1-2): (1-2).
Preferably, the conductive agent is acetylene black; the binder is polyvinylidene fluoride.
Preferably, the temperature of the forced air drying is 80-120 ℃, and the time is 1-4 h.
Preferably, the temperature of the vacuum drying is 100-150 ℃, the time is 8-12 h, and the vacuum degree is-0.1 MPa.
Preferably, the preparation method of the silicon electrodeposition solution comprises the following steps:
mixing a conductive auxiliary agent, an organic solvent and silicon halide to obtain silicon electrodeposition liquid;
the concentration of the conductive additive in the silicon electrodeposition liquid is 0.1-0.5 mol/L; the concentration of the silicon halide is 0.3-1 mol/L.
Preferably, the auxiliary electrode in the three-electrode system is a platinum sheet, and the reference electrode is a platinum sheet.
Preferably, the deposition potential in the constant potential electrodeposition is-1.5 to-3V, and the deposition time is 1 to 12 hours.
The invention also provides the application of the amorphous silicon-graphite composite material in the technical scheme or the amorphous silicon-graphite composite material prepared by the preparation method in the technical scheme as a negative electrode material in a lithium ion battery.
The invention provides an amorphous silicon-graphite composite material which comprises a current collector, a graphite conducting layer and an amorphous silicon deposition layer which are sequentially stacked. The graphite conducting layer in the amorphous silicon-graphite composite material can increase the transmission speed of electrons in the lithium ion de-intercalation process, and meanwhile, part of silicon material is contained, so that the effect of buffering silicon expansion is achieved, and the improvement of the cycle stability of the composite material is facilitated; the amorphous silicon can provide a lower activation energy barrier, and is beneficial to reducing the structural strain force of the composite material, further reducing the volume change of the composite material, and further being beneficial to improving the cycle stability and the rate capability of the amorphous silicon-graphite composite material.
The test results of the examples show that the amorphous silicon-graphite composite material provided by the invention still has the capacity of 1100mAh/g after being cycled for 50 times, has good cycle stability and excellent rate capability, and the first irreversible discharge capacity is only 885mAh g-1。
The invention also provides a preparation method of the amorphous silicon-graphite composite material in the technical scheme, which comprises the following steps: mixing graphite, a conductive agent, a binder and an organic solvent to obtain slurry; after the slurry is coated on a current collector, sequentially carrying out air blast drying and vacuum drying to obtain a current collector-graphite layer material; and (3) carrying out constant potential electrodeposition in a silicon-containing electrodeposition solution by using the current collector-graphite layer material as a working electrode by using a three-electrode system, and depositing on the surface of the graphite layer of the current collector-graphite layer material to obtain amorphous silicon so as to obtain the amorphous silicon-graphite composite material. The amorphous silicon-graphite composite material is compounded by the electrodeposition method, so that the amorphous silicon can be accommodated by the graphite, the compactness of the combination of the amorphous silicon and the graphite in the composite material is increased, and the structural stability of the amorphous silicon-graphite composite material is facilitated.
Drawings
FIG. 1 is a linear scan of an electrodeposition bath of amorphous silicon-graphite composite prepared in example 4;
FIG. 2 is an SEM image of an amorphous silicon-graphite composite material prepared in example 4;
FIG. 3 is an XRD pattern of the amorphous silicon-graphite composite material prepared in example 4;
FIG. 4 is a cyclic voltammogram of the amorphous silicon-graphite composite prepared in example 4 in a lithium ion battery;
fig. 5 is a capacity voltage diagram of the lithium ion battery prepared in application example 1;
fig. 6 is a graph of cycle performance of the lithium ion battery prepared in application example 1;
fig. 7 is a capacity voltage diagram of the lithium ion battery prepared in application example 2;
fig. 8 is a graph showing cycle performance of the lithium ion battery prepared in application example 2.
Detailed Description
The invention provides an amorphous silicon-graphite composite material which comprises a current collector, a graphite conducting layer and an amorphous silicon deposition layer which are sequentially stacked.
In the present invention, the current collector is preferably a copper foil. In the present invention, the thickness of the graphite conductive layer is preferably 5 to 15 μm, more preferably 8 to 12 μm, and most preferably 10 μm. In the invention, the thickness of the amorphous silicon deposition layer is preferably 450 to 550nm, more preferably 470 to 530nm, and most preferably 500 nm.
The invention also provides a preparation method of the amorphous silicon-graphite composite material in the technical scheme, which comprises the following steps:
mixing graphite, a conductive agent, a binder and an organic solvent to obtain slurry;
after the slurry is coated on a current collector, sequentially carrying out air blast drying and vacuum drying to obtain a current collector-graphite layer material;
and (3) carrying out constant potential electrodeposition in a silicon-containing electrodeposition solution by using the current collector-graphite layer material as a working electrode by using a three-electrode system, and depositing on the surface of the graphite layer of the current collector-graphite layer material to obtain amorphous silicon so as to obtain the amorphous silicon-graphite composite material.
The invention mixes graphite, conductive agent, binder and organic solvent to obtain slurry. The source of the graphite in the present invention is not particularly limited, and graphite known to those skilled in the art, such as commercially available graphite, can be used. In the present invention, the conductive agent is preferably acetylene black. In the present invention, the binder is preferably polyvinylidene fluoride. In the present invention, the organic solvent is preferably N-methylpyrrolidone (NMP). The mixing is not particularly limited in the present invention, and may be performed by a method known to those skilled in the art. Prior to said mixing, the present invention preferably grinds said graphite; the present invention is not particularly limited to the above-mentioned grinding, and the grinding may be carried out by a method known to those skilled in the art; the invention reduces the particle size of the graphite by grinding, so as to be beneficial to the full dispersion of the graphite in the slurry.
After the slurry is obtained, the current collector-graphite layer material is obtained by sequentially carrying out air blast drying and vacuum drying after the slurry is coated on the current collector. In the present invention, the current collector is preferably a copper foil; the source of the copper foil is not particularly limited in the present invention, and a copper foil known to those skilled in the art may be used. The coating method of the present invention is not particularly limited, and a coating method known to those skilled in the art may be used. In the invention, the coating thickness of the slurry on the current collector is preferably 100-200 μm. In the invention, the temperature of the forced air drying is preferably 80-120 ℃, more preferably 85-115 ℃, and further preferably 90-110 ℃; the time is preferably 1 to 4 hours, more preferably 1.5 to 3.5 hours, and still more preferably 2 to 3 hours. The invention removes the organic solvent and water in the slurry primarily by air-blast drying, and prevents the organic solvent from being filled in the vacuum environment to reduce the vacuum drying effect when the vacuum drying is directly carried out.
In the invention, the temperature of the vacuum drying is preferably 100-150 ℃, more preferably 105-145 ℃, and further preferably 110-140 ℃; the time is preferably 8-12 h, more preferably 8.5-11.5 h, and still more preferably 9-11 h; the degree of vacuum is preferably-0.1 MPa. The invention prevents the current collector from being oxidized in the drying process through vacuum drying.
After the current collector-graphite layer material is obtained, the invention utilizes a three-electrode system, takes the current collector-graphite layer material as a working electrode, carries out constant potential electrodeposition in silicon-containing electrodeposition liquid, and deposits on the graphite layer surface of the current collector-graphite layer material to obtain amorphous silicon, thus obtaining the amorphous silicon-graphite composite material. In the three-electrode system, the working electrode is the current collector-graphene composite material, the auxiliary electrode is preferably a platinum sheet, and the reference electrode is preferably a platinum sheet.
In the present invention, the process for preparing the silicon electrodeposit solution preferably comprises the steps of:
and mixing the conductive auxiliary agent, the organic solvent and the silicon halide to obtain the silicon electrodeposition liquid.
In the invention, the conductive aid added to the electrodeposition bath is preferably tetrabutylammonium chloride (TBACL) or tetrabutylammonium bromide (TBAB). In the present invention, the organic solvent is preferably propylene carbonate and/or ethylene carbonate. In the present invention, the silicon halide is preferably SiCl4. In the invention, the concentration of the conductive auxiliary agent in the silicon electrodeposition liquid is preferably 0.1-0.5 mol/L, more preferably 0.1-0.4 mol/L, and still more preferably 0.1-0.3 mol/L. The concentration of the silicon halide is preferably 0.3 to 1mol/L, more preferably 0.4 to 0.9mol/L, and still more preferably 0.5 to 0.8 mol/L.
In the invention, the conductive auxiliary agent is preferably dissolved in the organic solvent and then the silicon halide is added. Before the conductive auxiliary agent is dissolved in the organic solvent, the conductive substance is preferably dried in the present invention. In the present invention, the drying temperature is preferably 80 ℃ and the drying time is preferably 12 hours. In the present invention, the drying means is preferably an air-blast drying oven. The invention removes the moisture in the conductive substance by drying. The invention preferably continues to stir after the silicon halide is added; the stirring time is preferably 30 min; the stirring rate is not particularly limited in the present invention, and a stirring rate known to those skilled in the art may be used. In the present invention, the process for preparing the silicon electrodeposit is preferably carried out in a glove box.
In the present invention, the deposition potential of the potentiostatic electrodeposition is preferably-1.5 to-3V, more preferably-1.7 to-2.8V, still more preferably-2 to-2.5V; the deposition time is preferably 1-12 h, more preferably 3-10 h, and still more preferably 5-8 h. In the present invention, the potentiostatic electrodeposition is preferably carried out in a glove box. In the present invention, the environment of the potentiostatic electrodeposition is preferably H2O < 0.01ppm and O2Less than 0.01 ppm. The invention generates an amorphous silicon deposition layer on the graphite layer of the current collector-graphite layer material through constant potential electrodeposition.
After potentiostatic electrodeposition, the invention preferably cleans the resulting material. The cleaning agent is preferably an organic solvent, and more preferably propylene carbonate. The invention removes impurities and unreacted deposited ions on the surface of the material obtained by constant potential electrodeposition by cleaning, such as removing unreacted Si by cleaning4+And TBA in conductive agent+。
The invention also provides the amorphous silicon-graphite composite material prepared by the technical scheme or the application of the amorphous silicon-graphite composite material prepared by the preparation method in the technical scheme in a lithium ion battery. In the present invention, the amorphous silicon-graphite composite material is preferably a negative electrode material of a lithium ion battery.
In order to further illustrate the present invention, an amorphous silicon-graphite composite material, a method for preparing the same and applications thereof are described in detail below with reference to examples, but they should not be construed as limiting the scope of the present invention.
Example 1
Grinding graphite, and then mixing the ground graphite, a conductive agent acetylene black and a binder PVDF according to the weight ratio of 7: 1.5: adding 1.5 mass ratio of the mixture into a proper amount of NMP, uniformly mixing the mixture with the concentration of PVDF in the NMP of 0.025g/mL, coating the mixed slurry on a copper foil by using a coater, wherein the coating thickness is 100 micrometers, drying the copper foil in a forced air drying oven at 80 ℃ for 4 hours, and then transferring the copper foil to a vacuum drying oven to dry the copper foil in vacuum at 100 ℃ for 12 hours to obtain a current collector-graphite layer material;
putting tetrabutylammonium chloride into a blast drying oven, drying at 80 ℃ for 12h, transferring into a glove box, stirring until the tetrabutylammonium chloride is completely dissolved in an organic solvent propylene carbonate, and then adding SiCl4Continuously stirring for 30min to obtain silicon-containing electrodeposition liquid, wherein the concentration of tetrabutylammonium chloride in the silicon-containing electrodeposition liquid is 0.2mol/L, and SiCl is added4The concentration of (A) is 0.3 mol/L;
adopting a three-electrode system, wherein the working electrode is a current collector-graphite layer composite material, the auxiliary electrode is a platinum sheet, the reference electrode is a platinum sheet, and the working electrode and the reference electrode are arranged in a glove box (H) at normal temperature2O<0.01ppm，O2<0.01ppm) is carried out with constant potential electrodeposition, the deposition potential of the constant potential electrodeposition is-1.5V, and the deposition time is 1 h; and cleaning the material obtained by constant potential electrodeposition by using propylene carbonate after electrodeposition to obtain the amorphous silicon-graphite composite material.
Example 2
Grinding graphite, and then mixing the ground graphite, a conductive agent acetylene black and a binder PVDF according to the weight ratio of 7: 2: 1, adding a proper amount of NMP into the mixture according to the mass ratio, uniformly mixing the mixture with the concentration of PVDF in the NMP being 0.025g/mL, coating the mixed slurry on a copper foil by using a coater, wherein the coating thickness is 200 mu m, drying the copper foil for 3h at 100 ℃ in a forced air drying oven, and then transferring the copper foil to a vacuum drying oven for vacuum drying for 9h at 120 ℃ to obtain a current collector-graphite layer material;
putting tetrabutylammonium chloride as a conductive agent into a blast drying oven, drying at 80 ℃ for 12h, transferring the tetrabutylammonium chloride into a glove box, stirring until the tetrabutylammonium chloride is completely dissolved in propylene carbonate as an organic solvent, and then adding SiCl4Continuously stirring for 30min to obtain silicon-containing electrodeposition liquid, wherein the concentration of tetrabutylammonium chloride in the silicon-containing electrodeposition liquid is 0.3mol/L, and SiCl is added4The concentration of (A) is 0.5 mol/L;
adopting a three-electrode system, wherein the working electrode is a current collector-graphite layer composite material, the auxiliary electrode is a platinum sheet, the reference electrode is a platinum sheet, and the working electrode and the reference electrode are arranged in a glove box (H) at normal temperature2O<0.01ppm，O2<0.01ppm) is carried out with constant potential electrodeposition, the deposition potential of the constant potential electrodeposition is-2.4V, and the deposition time is 8 h; and cleaning the material obtained by constant potential electrodeposition by using propylene carbonate after electrodeposition to obtain the amorphous silicon-graphite composite material.
Example 3
Grinding graphite, and then mixing the ground graphite, a conductive agent acetylene black and a binder PVDF according to the proportion of 8: 1: 2, adding the mass ratio of the PVDF into a proper amount of NMP, uniformly mixing the mixture with the concentration of 0.025g/mL of the PVDF in the NMP, coating the mixed slurry on a copper foil by using a coater, wherein the coating thickness is 150 micrometers, drying the copper foil for 1h at 120 ℃ in a forced air drying oven, and then transferring the copper foil to a vacuum drying oven for vacuum drying for 8h at 150 ℃ to obtain a current collector-graphite layer material;
putting tetrabutylammonium chloride as a conductive agent into a blast drying oven, drying at 80 ℃ for 12h, transferring the tetrabutylammonium chloride into a glove box, stirring until the tetrabutylammonium chloride is completely dissolved in propylene carbonate as an organic solvent, and then adding SiCl4Continuously stirring for 30min to obtain silicon-containing electrodeposition liquid, wherein the concentration of tetrabutylammonium chloride in the silicon-containing electrodeposition liquid is 0.5mol/L, and SiCl is added4The concentration of (A) is 1 mol/L;
adopting a three-electrode system, wherein the working electrode is a current collector-graphite layer composite material, the auxiliary electrode is a platinum sheet, the reference electrode is a platinum sheet, and the working electrode and the reference electrode are arranged in a glove box (H) at normal temperature2O<0.01ppm，O2<0.01ppm) is carried out with constant potential electrodeposition, the deposition potential of the constant potential electrodeposition is-3V, and the deposition time is 12 h; and cleaning the material obtained by constant potential electrodeposition by using propylene carbonate after electrodeposition to obtain the amorphous silicon-graphite composite material.
Example 4
Grinding graphite, and then mixing the ground graphite, a conductive agent acetylene black and a binder PVDF according to the proportion of 8: 1: adding the mass ratio of 1 into a proper amount of NMP, uniformly mixing the NMP and the PVDF in an amount of 0.025g/mL in NMP, coating the mixed slurry on a copper foil by using a coater, wherein the coating thickness is 100 micrometers, drying the copper foil in a forced air drying oven at 80 ℃ for 2 hours, and then transferring the copper foil to a vacuum drying oven to dry the copper foil in a vacuum at 100 ℃ for 10 hours to obtain a current collector-graphite layer material;
putting tetrabutylammonium chloride as a conductive agent into a blast drying oven, drying at 80 ℃ for 12h, transferring the tetrabutylammonium chloride into a glove box, stirring until the tetrabutylammonium chloride is completely dissolved in propylene carbonate as an organic solvent, and then adding SiCl4Continuously stirring for 30min to obtain silicon-containing electrodeposition liquid, wherein the concentration of tetrabutylammonium chloride in the silicon-containing electrodeposition liquid is 0.1mol/L, and SiCl is added4The concentration of (A) is 0.5 mol/L;
adopting a three-electrode system, wherein the working electrode is a current collector-graphite layer composite material, the auxiliary electrode is a platinum sheet, the reference electrode is a platinum sheet, and the working electrode and the reference electrode are arranged in a glove box (H) at normal temperature2O<0.01ppm，O2<0.01ppm) is carried out, the deposition potential of the constant potential electrodeposition is-1.7V, and the deposition time is 4 h; and cleaning the material obtained by constant potential electrodeposition by using propylene carbonate after electrodeposition to obtain the amorphous silicon-graphite composite material.
The silicon-containing bath obtained in example 4 was scanned linearly with the following parameters: the scanning speed is 10mV/s, and the scanning voltage window is-3.5-0V. The linear scan results are shown in figure 1. As can be seen from FIG. 1, a reduction peak was observed at-1.65V, due to Si4+At this potential, a reduction reaction occurs to generate elemental silicon, whereby the deposition potential of the silicon film can be determined.
The amorphous silicon-graphite composite material obtained in example 4 was subjected to scanning electron microscope test, and the SEM image is shown in FIG. 2. As can be seen from fig. 2, the silicon film was deposited relatively uniformly on the surface of the current collector-graphite composite material, which was about 500nm thick.
The amorphous silicon-graphite composite material obtained in example 4 was subjected to X-ray diffraction measurement, and the obtained XRD pattern is shown in fig. 3. As can be seen from fig. 3, relatively sharp characteristic diffraction peaks are observed at 43.3 °, 50.4 ° and 74.1 °, and the characteristic diffraction peaks observed at 26.6 ° correspond to the standard card of graphite carbon (PDF #26-1080), from the angle and the peak intensity, and correspond to the standard card of copper (PDF # 04-0836); at the same time, a weak and broad amorphous diffraction peak was observed at 21.8 ° 2 θ, which is caused by the amorphous structure of electrodeposited silicon.
Application example 1
The amorphous silicon-graphite composite material obtained in example 4 is used as a negative electrode material of a lithium ion battery to assemble the lithium ion battery, wherein the positive electrode material is a lithium sheet, and the electrolyte is LiPF6A solution obtained by dissolving ethylene carbonate and dimethyl carbonate (EC: DMC ═ 1:1) in a mixed solvent.
Cyclic voltammetry tests were performed on the lithium ion battery obtained in example 1, and the obtained cyclic voltammogram is shown in fig. 4. As can be seen from fig. 4, a broad reduction peak was observed around 0.67V during the first cycle, which is mainly responsible for the decomposition of the electrolyte and the formation of the solid electrolyte membrane, and also responsible for the first irreversible capacity, which peak no longer appears in the following cycles; the latter cyclic reduction peak appears around 0.18V, which is mainly the reduction reaction of the material during the discharge process; and two oxidation peaks appear around 0.28 and 0.36V, which are mainly oxidation reactions of the material during charging; the positions and the intensities of the reduction peak and the oxidation peak are not greatly changed in the subsequent circulation process, which indicates that the material has good reaction reversibility and circulation stability.
The lithium ion battery obtained in example 1 was subjected to a capacity voltage test, and the test result was shown in fig. 5. As can be seen from FIG. 5, the graph is a capacity-voltage graph of the first three times under a current density of 100mA/g, the first discharge specific capacity is 2078mAh/g, the charge specific capacity is 1460mAh/g, the corresponding coulombic effect is 70%, and the first large irreversible capacity is a common phenomenon in silicon-based materials; during the charging and discharging process, a discharging platform can be observed at about 0.18V, corresponding to the alloying reaction between silicon and lithium ions, which is consistent with the analysis result of the cyclic voltammetry curve; the material can effectively inhibit the volume change of silicon and improve the electrochemical performance.
The lithium ion battery obtained in the application example 1 was subjected to a cycle performance test, and the obtained test result is shown in fig. 6. As can be seen from fig. 6, which is a graph of cycle performance for 50 cycles at a current density of 100mA/g, the specific discharge capacity for the second cycle was 1610mAh/g, and the capacity fade for the second cycle was mainly attributed to SEI film formation, electrolyte consumption, and irreversible lithium deintercalation, compared to the first specific discharge capacity; after 50 times of charge and discharge, the discharge capacity is still maintained at 1206mAh/g, and compared with the discharge specific capacity of the second cycle, the discharge capacity still maintains 74.9 percent of specific capacity, and the excellent cycle stability is shown; after the first few cycles, the coulombic efficiency is basically stabilized above 99% except for small fluctuation, which shows that the material has better electrochemical performance.
Application example 2
The amorphous silicon-graphite composite material obtained in example 2 is used as a negative electrode material of a lithium ion battery to assemble the lithium ion battery, wherein the positive electrode material is a lithium sheet, and the electrolyte is LiPF6A solution obtained by dissolving ethylene carbonate and dimethyl carbonate (EC: DMC ═ 1:1) in a mixed solvent.
The lithium ion battery obtained in example 2 was subjected to a capacity voltage test, and the test result was shown in fig. 7. As can be seen from fig. 7, the graph is a capacity-voltage graph of the first three times under a current density of 100mA/g, the first discharge specific capacity is 2621mAh/g, the charge specific capacity is 1876mAh/g, and the corresponding coulomb effect is 71%, which is slightly better than the first charge-discharge performance obtained in application example 1, because the deposition time is long and more silicon occupies the whole material, thereby improving the first discharge capacity of the material. The specific discharge capacity of the second ring is 1498mAh/g, and the first irreversible capacity reaches 1123mAh/g, which is attributed to larger volume expansion caused by more silicon, so that the whole structure of the material is damaged. During charging and discharging, a discharge plateau around 0.18V can be observed, consistent with the material of application 1.
And (3) carrying out cycle performance test on the lithium ion battery obtained in the application example 2, wherein the obtained test result is shown in figure 8. As can be seen from fig. 8, which is a graph of cycle performance of the material at a current density of 100mA/g for 50 cycles, the specific discharge capacity at the second cycle was 1498mAh/g, and the capacity fade at the second time was mainly attributed to SEI film formation, large consumption of electrolyte, and irreversible lithium deintercalation, compared to the first specific discharge capacity. After 50 times of charging and discharging, the specific discharge capacity is only 652mAh/g, and compared with the specific discharge capacity of the second cycle, the specific discharge capacity is only 43.5 percent, and the poor cycle stability is shown. This can be attributed to the fact that long term deposition brings a thicker silicon film, resulting in poor overall conductivity and greater volume expansion of the material, reducing the cycling stability of the material. From the coulombic efficiency chart, the poor cycle stability of the material is also fully explained.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
Claims (10)
1. The amorphous silicon-graphite composite material is characterized by comprising a current collector, a graphite conducting layer and an amorphous silicon deposition layer which are sequentially stacked.
2. A method for preparing the amorphous silicon-graphite composite material of claim 1, comprising the steps of:
mixing graphite, a conductive agent, a binder and an organic solvent to obtain slurry;
after the slurry is coated on a current collector, sequentially carrying out air blast drying and vacuum drying to obtain a current collector-graphite layer material;
and (3) carrying out constant potential electrodeposition in a silicon-containing electrodeposition solution by using the current collector-graphite layer material as a working electrode by using a three-electrode system, and depositing on the surface of the graphite layer of the current collector-graphite layer material to obtain amorphous silicon so as to obtain the amorphous silicon-graphite composite material.
3. The preparation method according to claim 2, wherein the mass ratio of the graphite to the conductive agent to the binder is (7-8): (1-2): (1-2).
4. The production method according to claim 2 or 3, wherein the conductive agent is acetylene black; the binder is polyvinylidene fluoride.
5. The preparation method according to claim 2, wherein the temperature of the forced air drying is 80-120 ℃ and the time is 1-4 h.
6. The preparation method according to claim 2, wherein the temperature of the vacuum drying is 100-150 ℃, the time is 8-12 h, and the vacuum degree is-0.1 MPa.
7. The method of claim 2, wherein the silicon electrodepositing solution is prepared by a method comprising the steps of:
mixing a conductive auxiliary agent, an organic solvent and silicon halide to obtain silicon electrodeposition liquid;
the concentration of the conductive additive in the silicon electrodeposition liquid is 0.1-0.5 mol/L; the concentration of the silicon halide is 0.3-1 mol/L.
8. The method according to claim 2, wherein the auxiliary electrode in the three-electrode system is a platinum sheet and the reference electrode is a platinum sheet.
9. The preparation method according to claim 2, wherein the deposition potential in the constant potential electrodeposition is-1.5 to-3V, and the deposition time is 1 to 12 hours.
10. The amorphous silicon-graphite composite material according to claim 1 or the amorphous silicon-graphite composite material prepared by the preparation method according to any one of claims 2 to 9 is used as a negative electrode material in a lithium ion battery.
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