CN113675385B - Nanoscale silicon-carbon composite negative electrode material, preparation method and lithium ion battery - Google Patents
Nanoscale silicon-carbon composite negative electrode material, preparation method and lithium ion battery Download PDFInfo
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Abstract
The invention provides a nanoscale silicon-carbon composite negative electrode material, a preparation method and a lithium ion battery, and the preparation method comprises the following steps: s1, slowly titrating a sodium silicate solution and an ammonium chloride solution in a high-speed stirring process to obtain a white precipitate; washing the white precipitate with ethanol, separating, drying, and reacting at 465-475 ℃ to obtain SiO 2 (ii) a Mixing SiO 2 And Mg in a molar ratio of 1:1.05 to 1.2, and completely reacting at 640 to 660 ℃ under the protection of nitrogen; dissolving the product after reaction, and centrifugally washing and drying to obtain a nano-scale silicon material; s2, preparing a nano carbon fluoride material by using nano carbon or nano multilayer graphene as a carbon source and adopting a gas phase fluorination method; and S3, preparing the nano silicon-carbon composite negative electrode material by using nano silicon material, nano carbon fluoride material, styrene butadiene rubber, carboxymethyl cellulose and conductive carbon black as raw materials. The lithium ion battery prepared from the nanoscale silicon-carbon composite negative electrode material has good cycle performance.
Description
Technical Field
The invention relates to a nanoscale silicon-carbon composite negative electrode material, a preparation method and a lithium ion battery, and belongs to the technical field of lithium ion batteries.
Background
The lithium ion battery is a secondary battery formed by respectively using two compounds capable of reversibly intercalating and deintercalating lithium ions as positive and negative electrodes, not only maintains the main advantages of high voltage and high capacity of the lithium battery, but also has the remarkable characteristics of long cycle life and good safety performance, shows wide application prospects in various aspects of portable electronic equipment, electric automobiles, space technology, national defense industry and the like, and quickly becomes a research hotspot which is widely concerned in recent decades.
Silicon is currently known for its specific capacity (4200mAh.g) -1 ) The highest lithium ion battery cathode material, however, due to its huge volume effect, the silicon electrode material will be pulverized and peeled off from the current collector during the charging and discharging process, so that the active material and the active material, and the active material and the current collector are lostElectrical contact, while continuing to form a new solid electrolyte layer (SEI), ultimately leads to deterioration of the electrochemical performance of the lithium ion battery.
In recent research efforts, a number of methods have been used to address the problem of volume effects of silicon during cycling. Among them, the compounding with a carbon material and silicon is an important technical means. However, such a negative electrode material excellent in cycle performance is still relatively lacking in the prior art.
Disclosure of Invention
The invention provides a nanoscale silicon-carbon composite negative electrode material, a preparation method and a lithium ion battery, which can effectively solve the problems.
The invention is realized in the following way:
a preparation method of a nanoscale silicon-carbon composite anode material comprises the following steps:
s1, slowly titrating a sodium silicate solution and an ammonium chloride solution in a high-speed stirring process to obtain a white precipitate; washing the white precipitate with ethanol, separating, drying, and reacting at 465-475 ℃ to obtain SiO 2 (ii) a Mixing SiO 2 And Mg in a molar ratio of 1:1.05 to 1.2, and completely reacting at 640 to 660 ℃ under the protection of nitrogen; dissolving the reacted product, centrifugally washing and drying to obtain nano silicon material;
s2, preparing a nano carbon fluoride material by using nano carbon or nano multilayer graphene as a carbon source and adopting a gas phase fluorination method;
and S3, preparing the nano silicon-carbon composite negative electrode material by using nano silicon material, nano carbon fluoride material, styrene Butadiene Rubber (SBR), carboxymethyl cellulose (CMC) and conductive carbon black (SP) as raw materials.
As a further improvement, the sodium silicate solution and the ammonium chloride solution are respectively formed by dissolving sodium silicate and ammonium chloride in a mixed solvent of deionized water and ethanol; the volume ratio of the deionized water to the ethanol is 1:0.5 to 2.
As a further improvement, the concentration of the sodium silicate solution is 0.02-0.04 g/mL; the concentration of the ammonium chloride solution is 0.006-0.01 g/mL.
As a further improvement, the volume ratio of the sodium silicate solution to the ammonium chloride solution is 1-4: 1; the time for slow titration is 2-5 h.
As a further improvement, the gas phase fluorination method comprises the steps of putting a carbon source into fluorination equipment, introducing a fluorination gas, keeping the pressure at 90-120 kPa, and reacting at 350-500 ℃ for 8-16 h to obtain a nano carbon fluoride material; wherein the molar ratio of the fluorine to the carbon is 0.7-0.9: 1.
as a further improvement, the fluoridation gas is one or more of xenon difluoride, nitrogen trifluoride, fluorine gas, boron trifluoride or fluorine-argon mixed gas.
As a further improvement, the mass ratio of the nano-scale silicon material, the nano-scale carbon fluoride material, the styrene butadiene rubber, the carboxymethyl cellulose and the conductive carbon black is 65-75: 100 to 110:4 to 6:8 to 12.
As a further improvement, the step S3 is specifically: mixing the nano-scale silicon material, the nano-scale carbon fluoride material, the styrene butadiene rubber, the carboxymethyl cellulose and the conductive carbon black, and dispersing by using a nano-dispersion machine, wherein the dispersion speed is 1600-2000 rpm, the dispersion time is 2-3 h, and the dispersion temperature is 20-30 ℃.
A nano-scale silicon-carbon composite cathode material is prepared by the method.
The active material of the cathode of the lithium ion battery is the nanoscale silicon-carbon composite cathode material.
The invention has the beneficial effects that: the nanoscale silicon-carbon composite negative electrode material adopts nanoscale carbon fluoride or graphene fluoride as a nanoscale silicon material negative electrode additive, and when the nanoscale carbon fluoride or graphene fluoride reacts with lithium ions to generate lithium fluoride and carbon which are dispersed around a silicon material electrode during first charging, so that the volume expansion of the silicon material negative electrode in the charging and discharging processes can be effectively inhibited, and the volume effect is overcome. The carbon generated by the reaction can also play a role of a conductive agent, and the cycle performance of the lithium ion battery is effectively improved.
The invention can prepare the nano-silicon material with the grain diameter of about 50-200 nanometers by selecting the ethanol and controlling the slow titration, and compared with the honeycomb-shaped silicon material, the nano-silicon material has good electrochemical performance and cycle performance, thereby improving the cycle performance of the lithium ion battery.
In the preparation process of the nano-scale silicon-carbon composite negative electrode material, the nano-scale silicon material, the nano-scale carbon fluoride material, the styrene butadiene rubber, the carboxymethyl cellulose, the conductive carbon black and other materials are subjected to nanocrystallization treatment through nano dispersion, so that the cycle performance of the nano-scale silicon-carbon composite negative electrode material is further improved.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings that are required to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and that those skilled in the art can also obtain other related drawings based on the drawings without inventive efforts.
FIG. 1 is an X-ray diffraction pattern of an example sample provided in example 1 of the present invention.
FIG. 2 is a Scanning Electron Microscopy (SEM) image of a sample provided in example 1 of the present invention.
FIG. 3 is a TEM image of transmission electron microscopy analysis of a sample 4h-Si provided in example 1 of the present invention.
FIG. 4 is an SEM image of a nanosized carbon fluoride material provided in example 2 of the present invention.
Fig. 5 is a performance graph of the nanoscale fluorinated graphene material provided in example 3 of the present invention.
Fig. 6 is a first charge-discharge curve of a lithium ion battery prepared from the nano-scale silicon-carbon composite anode material provided in embodiment 4 of the present invention.
Fig. 7 is a graph of the cycle performance of a lithium ion battery fabricated from the nanoscale silicon-carbon composite anode material provided in example 4 of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be described in detail and completely below with reference to the accompanying drawings of the embodiments of the present invention. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments of the present invention without any creative effort belong to the protection scope of the present invention. Thus, the following detailed description of the embodiments of the present invention, as presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In the description of the present invention, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or to imply that the number of technical features indicated is significant. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means two or more unless specifically defined otherwise.
The embodiment of the invention provides a preparation method of a nano-scale silicon-carbon composite anode material, which comprises the following steps:
s1, slowly titrating a sodium silicate solution and an ammonium chloride solution in a high-speed stirring process to obtain a white precipitate; washing the white precipitate with ethanol, separating, drying, and reacting at 465-475 ℃ to obtain SiO 2 (ii) a Mixing SiO 2 And Mg in a molar ratio of 1:1.05 to 1.2, and completely reacting at 640 to 660 ℃ under the protection of nitrogen; and dissolving the Mg and MgO products after reaction by using hydrochloric acid, wherein the concentration of the hydrochloric acid is 5-15 wt%, and centrifugally washing and drying to obtain the nano-scale silicon material.
As a further improvement, the sodium silicate solution and the ammonium chloride solution are respectively formed by dissolving sodium silicate and ammonium chloride in a mixed solvent of deionized water and ethanol; the volume ratio of the deionized water to the ethanol is 1:0.5 to 2.
As a further improvement, the concentration of the sodium silicate solution is 0.02-0.04 g/mL; the concentration of the ammonium chloride solution is 0.006-0.01 g/mL.
As a further improvement, the volume ratio of the sodium silicate solution to the ammonium chloride solution is 1-4: 1; the time for slow titration is 2-5 h.
The step can prepare the nano-scale silicon material with the grain diameter of about 50-200 nanometers through the selection of ethanol and the control of slow titration, is granular, and has good electrochemical performance and cycle performance compared with honeycomb-shaped silicon materials.
And S2, preparing the nano carbon fluoride material by using nano carbon or nano multilayer graphene as a carbon source and adopting a gas-phase fluorination method. The gas phase fluorination method comprises the steps of putting a carbon source into fluorination equipment, introducing a fluorination gas, keeping the pressure at 90-120 kPa, and reacting at 350-500 ℃ for 8-16 h to obtain a nanoscale carbon fluoride material; wherein the molar ratio of the fluorine to the carbon is 0.7-0.9: 1. the fluoridizing gas is one or more of xenon difluoride, nitrogen trifluoride, fluorine gas, boron trifluoride or mixed gas of fluorine gas and argon. The nano carbon fluoride material prepared in the step keeps the morphological structure characteristics of micron particles, the interface contact area of electrolyte and the carbon fluoride material is increased, and the specific surface area of nano carbon after fluorination is obviously increased; on the other hand, the material has high specific capacity and specific energy, and the cycle performance of the material is further improved.
And S3, preparing the nano silicon-carbon composite negative electrode material by using nano silicon material, nano carbon fluoride material, styrene Butadiene Rubber (SBR), carboxymethyl cellulose (CMC) and conductive carbon black (SP) as raw materials.
As a further improvement, the mass ratio of the nano-scale silicon material, the nano-scale carbon fluoride material, the styrene butadiene rubber, the carboxymethyl cellulose and the conductive carbon black is 65-75: 100 to 110:4 to 6:8 to 12.
As a further improvement, the step S3 is specifically: mixing the nano-scale silicon material, the nano-scale carbon fluoride material, the styrene butadiene rubber, the carboxymethyl cellulose and the conductive carbon black, and dispersing by using a nano-dispersion machine, wherein the dispersion speed is 1600-2000 rpm, the dispersion time is 2-3 h, and the dispersion temperature is 20-30 ℃. The step is to carry out nanocrystallization treatment on the raw materials, so that the cycle performance of the nano silicon-carbon composite anode material is further improved.
The embodiment of the invention also provides a nano-scale silicon-carbon composite anode material which is prepared by adopting the method.
The embodiment of the invention also provides a lithium ion battery, and the active material of the negative electrode of the lithium ion battery is the nanoscale silicon-carbon composite negative electrode material.
EXAMPLE 1 preparation of nanoscale silicon Material
1. 5g of sodium silicate are weighed out and dissolved in 192ml of deionized water and absolute ethanol 1:1, 1.4g of ammonium chloride dissolved in 192ml of deionized water and absolute ethanol 1:1, and (2) dissolving the mixture in the solution.
Slowly titrating the sodium silicate solution by 2.192ml of ammonium chloride solution for 3 hours and 4 hours respectively under high-speed stirring to obtain a milky white substance.
3. And (4) performing high-speed centrifugal washing for multiple times by using ethanol to obtain a white precipitate.
4. Drying the obtained white precipitate at 80 ℃, and reacting at 470 ℃ to obtain SiO 2 。
5. Mixing SiO 2 And Mg in a ratio of 1:1.1 in the stoichiometric ratio under the protection of argon and 650 deg.c (the temperature raising rate is 5 deg.c/min) for 3 hr.
6. Mg and MgO which have not reacted are dissolved in 10% hydrochloric acid and washed by centrifugation.
7. The resulting tan-colored material was dried in a drying oven at 80 ℃. Finally obtaining the nano-Si. The prepared samples were divided into 3h-Si and 4h-Si according to the addition time of absolute ethanol.
The X-ray diffraction pattern of the example sample is shown in fig. 1, from which the crystalline properties of silicon can be seen. And a small SiO in the 4h-Si diffractogram 2 Peak, which illustrates the crystal grain ratio of 4h-SiThe crystal grains of 3h-Si are small enough to be in SiO 2 And Mg at a mass ratio of 1.1 SiO is not completely converted into Mg 2 And reduced to Si. Thus for SiO with smaller particles 2 In terms of the quality of Mg should be increased by a certain proportion to make SiO 2 Can be completely reduced into Si.
The microscopic topography characterization of the Scanning Electron Microscopy (SEM) of the example samples is shown in fig. 2. As shown in fig. 2, it is evident that the morphology of the formed silicon sample changed as the addition rate of the absolute ethanol was decreased. As the length of time of addition of absolute ethanol increased, the particle size of the silicon sample decreased significantly and appeared flocculent. When the time for adding ethanol was controlled to be three hours, the silicon particle size was 100-200nm (fig. 2. A), and the particle size was several tens of nanometers when the time was controlled to be four hours (fig. 2. B). The smaller the particle size, the better the effect of relieving the stress caused by volume expansion in the charging and discharging process, and the surface area and the charging and discharging efficiency can be improved. The structure is fluffy cotton flocculent, and more volume expansion space can be provided, which has great benefit on prolonging the cycle life.
Example 4h-Si microscopic morphology by TEM transmission electron microscopy is shown in FIG. 3, which shows that the sample is similar to a feather structure and a lamellar structure grows outwards from a scaffold. And the support on the sample micro-topography is polycrystalline, and the outward-derived layer of the sample support is amorphous as can be seen from an electron diffraction pattern. This indicates that the sample contains a mixture of crystalline and amorphous.
EXAMPLE 2 preparation of nanosized fluorocarbons
The nano-scale carbon fluoride material is prepared by using nano carbon as a carbon source and adopting a gas phase fluorination method. Putting the nano carbon into fluorination equipment, introducing fluorine gas, keeping the pressure at 90kPa, and reacting for 15h at 400 ℃ to obtain NCF0.8 with the fluorine-carbon ratio of about 0.8. Putting the nano carbon into fluorination equipment, introducing fluorine gas, keeping the pressure at 100kPa, and reacting for 12h at the temperature of 420 ℃ to obtain NCF0.9 with the fluorine-carbon ratio of about 0.9. Putting the nano-carbon into fluorination equipment, introducing fluorine gas, keeping the pressure at 130kPa, and reacting for 16h at 500 ℃ to obtain NCF1.0 with the fluorine-carbon ratio of about 1.0. Fig. 4 is an SEM image thereof, wherein the nanocarbon substantially maintains the morphological feature of the nanocarbon aggregated into micro-particles after fluorination, and the morphological feature improves the interface contact area between the electrolyte and the carbon fluoride material. Meanwhile, the specific surface area of the nano-carbon is remarkably increased after fluorination (table 1), so that the agglomeration phenomenon among nano-carbon particles is reduced due to the generation of fluorine-carbon bonds on the surface of the carbon. Compared with NCF0.9, the specific surface area of the NCF1.0 material is obviously reduced, and the energy can be obtained when the morphological structure is extremely collapsed.
TABLE 1 specific surface area of nanocarbons and corresponding nanocarbon fluoride materials.
Example 3 preparation of nanoscale fluorinated graphene
The nanoscale fluorinated graphene material is prepared by using nanoscale multi-layer graphene as a carbon source and adopting a gas-phase fluorination method. Putting 10g of nano-scale graphene raw material into fluorination equipment, introducing fluorinated gas nitrogen trifluoride, keeping the pressure at 100kPa, and reacting for 12 hours at 440 ℃ to obtain about 22.9g of nano-scale fluorinated graphene, wherein the fluorine-carbon ratio is calculated to be 0.8 (GF 0.8). In addition, 10g of graphene raw material is put into a fluorination device, boron trifluoride serving as a fluorination gas is introduced, the pressure is kept at 90kPa, and the reaction is carried out for 10 hours at 480 ℃ to obtain 24.5g of nanoscale fluorinated graphene, wherein the fluorine-carbon ratio is about 0.90 (GF 0.9). The series of materials show more excellent performance (figure 5), under the current of 1A/g, the specific capacities of GF0.8 and GF0.9 materials are 731 and 767mAh/g respectively, the specific energies are all about 1900Wh/kg, and the median voltages are 2.8 and 2.6V respectively.
EXAMPLE 4 preparation of nanoscale silicon-carbon composite negative electrode Material
The nano-scale silicon material prepared in example 1 and the nano-scale carbon fluoride prepared in example 2 were used as materials to prepare a negative electrode material. Wherein, the Si is NCF0.9, the SBR is CMC SP =70: and mixing the raw materials, and dispersing by using a nano dispersion machine at the dispersion speed of 1800rpm for 2.5h at the dispersion temperature of 25 ℃ to obtain the nano silicon-carbon composite negative electrode material. The button cell prepared according to the conventional method has a first charge-discharge curve as shown in fig. 6, which shows a obvious discharge platform around 3V, and the reaction is as follows: 0.9Li + + CF0.9=0.9LiF + C, followed by the normal silicon cathode alloying reaction.
During the subsequent cycle, the charge and discharge potential interval is lower than 3V, so that LiF and C are dispersed around Si to inhibit the volume expansion of Si during the charge and discharge process and raise the cycle performance. The cycle performance is shown in fig. 7.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made without departing from the spirit and principle of the present invention shall fall within the protection scope of the present invention.
Claims (7)
1. The preparation method of the nano-scale silicon-carbon composite anode material is characterized by comprising the following steps of:
s1, slowly titrating a sodium silicate solution and an ammonium chloride solution in a high-speed stirring process to obtain a white precipitate; washing the white precipitate with ethanol, separating, drying, and reacting at a high temperature of 465 to 475 ℃ to obtain SiO 2 (ii) a Mixing SiO 2 And Mg in a molar ratio of 1:1.05 to 1.2, and reacting completely at 640 to 660 ℃ under the protection of nitrogen; dissolving the reacted product, centrifugally washing and drying to obtain nano silicon material; the concentration of the sodium silicate solution is 0.02 to 0.04g/mL; the concentration of the ammonium chloride solution is 0.006 to 0.01g/mL;
s2, preparing a nano carbon fluoride material by using nano carbon as a carbon source and adopting a gas phase fluorination method;
s3, preparing the nano-silicon-carbon composite negative electrode material by using the nano-silicon material obtained in the step S1, the nano-carbon fluoride material obtained in the step S2, styrene butadiene rubber, carboxymethyl cellulose and conductive carbon black as raw materials;
the step S3 specifically comprises the following steps: mixing the nano-scale silicon material, the nano-scale carbon fluoride material, styrene butadiene rubber, carboxymethyl cellulose and conductive carbon black, and dispersing by using a nano-dispersion machine, wherein the dispersion speed is 1600 to 2000rpm, the dispersion time is 2 to 3h, and the dispersion temperature is 20 to 30 ℃;
the volume ratio of the sodium silicate solution to the ammonium chloride solution is 1 to 4:1; the time for slow titration is 2 to 5 hours;
the micro-morphology of the nano-scale silicon material is a feather-like structure with a sheet structure growing outwards from a support; the scaffold is polycrystalline, while the outwardly grown sheet structure of the scaffold is amorphous.
2. The method for preparing the nano-scale silicon-carbon composite anode material according to claim 1, wherein the nano-scale carbon is nano-scale multi-layer graphene.
3. The method for preparing the nano-scale silicon-carbon composite anode material according to claim 1, wherein the sodium silicate solution and the ammonium chloride solution are respectively formed by dissolving sodium silicate and ammonium chloride in a mixed solvent of deionized water and ethanol; the volume ratio of the deionized water to the ethanol is 1:0.5 to 2.
4. The preparation method of the nano silicon-carbon composite anode material as claimed in claim 1, wherein the gas phase fluorination method comprises the steps of putting a carbon source into fluorination equipment, introducing fluorination gas, keeping the pressure at 90 to 120kPa, and reacting at 350 to 500 ℃ for 8 to 16 hours to obtain the nano carbon fluoride material; wherein the molar ratio of the fluorine to the carbon is 0.7 to 0.9:1.
5. the method for preparing the nano-scale silicon-carbon composite anode material according to claim 4, wherein the fluorinated gas is one or more of xenon difluoride, nitrogen trifluoride, fluorine gas, boron trifluoride, or a mixed gas of fluorine and argon.
6. A nanoscale silicon-carbon composite anode material, characterized in that the nanoscale silicon-carbon composite anode material is prepared by the method of any one of claims 1 to 5.
7. A lithium ion battery, characterized in that the active material of the negative electrode of the lithium ion battery is the nanoscale silicon-carbon composite negative electrode material according to claim 6.
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