A nano-silicon-carbon composite negative electrode material containing nanofiber carbon and a preparation method thereof

Abstract

The application relates to a nano-silicon-carbon composite negative material containing nanofiber carbon and a preparation method thereof. High-temperature pitch powder and ethyl cellulose are dissolved in tetrahydrofuran; then nano-silicon powder is added into deionized water and ultrasonically dispersed; carboxymethyl cellulose sodium and graphite powder are added into the dispersion liquid, and ultrasonic stirring is conducted to uniformly mix the carboxymethyl cellulose sodium and the graphite powder, so as to obtain a water dispersion liquid; then the mother liquor containing the high-temperature pitch powder and the ethyl cellulose is injected into the water solution containing the uniformly mixed nano-silicon powder, the graphite powder and the carboxymethyl cellulose sodium, and high-speed stirring is continuously conducted during the injection process; finally, a homogeneous precursor is obtained through spray drying, and high-temperature carbonization is conducted after high-speed fusion. The material can effectively relieve the expansion of nano-particles, the conductivity is not affected by the volume expansion change, and the performance is excellent.

Description

TECHNICAL FIELD

[0001] The present application relates to the preparation of silicon negative electrode material for lithium ion battery, and particularly relates to a nano-silicon-carbon composite negative electrode material containing nanofiber carbon and a preparation method thereof. BACKGROUND

[0002] The silicon negative electrode material has high capacity (3579 mAh / g, Li15Si4) and low potential (~370 mV vs. Li / Li+), and becomes the best choice for high-energy-density lithium ion battery negative electrode material. However, the silicon has a huge volume change during the process of deintercalating lithium, which easily causes the active material silicon particles to lose electrical contact and fail to exert capacity, thereby reducing the cycle life. At present, the commonly used method is to nanoize the silicon and then composite it with graphite materials and perform surface carbon coating to prepare a nano-silicon-carbon composite negative electrode material, so as to improve the electrical conductivity of the nano-silicon and improve the cycle life. However, the nano-silicon still has a large volume change during the process of deintercalating lithium, which produces a great stress and strain, causes the surface carbon coating layer to fall off, leads to the pulverization of the composite material, and makes the combination between the active material and the current collector loose, thereby causing the silicon material to peel off from the surface of the graphite carrier and lose electrical contact, and the cycle capacity rapidly decays. Moreover, after the silicon expands and shrinks for many times, the volume expansion of the particles causes the particles to press against each other, the electrode will be broken and fall off, and finally completely loses electrical contact with the current collector, resulting in a sharp decrease in capacity and poor cycle stability.

[0003] Therefore, how to provide a nano-silicon-carbon composite negative electrode material which effectively alleviates the expansion of nano-particles and does not affect the electrical conductivity of the material is a technical problem to be solved by those skilled in the art. SUMMARY

[0004] In view of this, in order to improve the electrical conductivity of the nano-silicon material and avoid the active material nano-silicon material from losing electrical contact and failing to exert capacity, the present application provides a nano-silicon-carbon composite negative electrode material containing nanofiber carbon and a preparation method thereof.

[0005] By introducing the nanofiber carbon into the nano-silicon-carbon composite negative electrode material, on the one hand, the nano-silicon material can be well bound to the surface of the graphite carrier to adapt to the volume change of the nano-silicon material, and on the other hand, the nanofiber carbon forms a conductive channel on the surface of the nano-silicon particles, thereby avoiding the nano-silicon from losing electrical contact and failing to exert capacity during the repeated volume change process, and thus a higher cycle life is obtained.

[0006] It should be noted that the nano-silicon-carbon composite negative electrode material containing nanofiber carbon provided by the present application includes the preparation of a composite material composed of nanofiber carbon, a surface split carbon layer, nano-silicon and graphite and a method and steps for using the composite material as a silicon-carbon composite material for lithium ion battery, wherein the preparation method involved in the present application is as follows:

[0007] Firstly, high temperature pitch powder and ethyl cellulose are dissolved in tetrahydrofuran as a mother liquor for standby, while the nano silicon powder is added to deionized water for ultrasonic dispersion, then carboxymethyl cellulose sodium and graphite powder are added to the dispersion liquid for ultrasonic stirring and mixing uniformly to obtain a uniformly mixed water dispersion liquid, then the mother liquor containing high temperature pitch powder and ethyl cellulose is slowly injected into the uniformly mixed water solution of nano silicon, graphite and carboxymethyl cellulose sodium, and high-speed stirring is continuously carried out during the injection process, on the one hand, the pitch and ethyl cellulose are precipitated to form high molecular fiber filaments, on the other hand, the components are uniformly dispersed in the mixed solution, finally, the uniformly dispersed precursor is obtained by spray drying, and the nano silicon-carbon composite negative electrode material containing nano fiber carbon is obtained after high-speed fusion and high temperature carbonization.

[0008] Specifically, one of the purposes of the present application is to provide a nano silicon-carbon composite negative electrode material containing nano fiber carbon.

[0009] Among them, the tetrahydrofuran solution of pitch and ethyl cellulose is used as the mother material for generating high molecular fiber filaments, and the nano fiber filaments are generated by injecting into the high-speed stirring water solution for rapid precipitation, and then the nano fiber carbon is obtained by high temperature carbonization;

[0010] Moreover, the solid solute in the precursor solution of the nano silicon-carbon composite negative electrode material is mainly composed of 10-15wt.% of high temperature pitch powder, 4-6wt.% of ethyl cellulose, 15wt.% of spherical nano silicon powder, 3-5wt.% of carboxymethyl cellulose sodium and 59-68wt.% of graphite powder.

[0011] Another purpose of the present application is to provide a preparation method of the above-mentioned nano silicon-carbon composite negative electrode material containing nano fiber carbon, and the method specifically comprises the following steps:

[0012] 1) The high temperature pitch powder and ethyl cellulose are weighed according to the above-mentioned formula and added to tetrahydrofuran for dissolution, and the solid content is controlled in the range of 40-50wt.% as a mother liquor for generating high molecular fibers for standby;

[0013] 2) The spherical nano silicon powder is weighed according to the above-mentioned formula and added to deionized water for ultrasonic dispersion to obtain a nano silicon powder dispersion liquid with a solid content of 3-5wt.%, then graphite and carboxymethyl cellulose sodium are added for ultrasonic stirring and mixing uniformly to obtain a homogeneous dispersion liquid;

[0014] 3) The high molecular fiber mother liquor prepared in step 1) is slowly injected into the homogeneous dispersion liquid obtained in step 2), and high-speed stirring is carried out at a speed of 2000-3000r / min during the injection process, so that the pitch and ethyl cellulose are precipitated to form high molecular fiber filaments, and the mixture is uniformly mixed to obtain a homogeneous precursor solution;

[0015] 4) spray drying the homogeneous precursor solution obtained in step 3) to obtain a homogeneous precursor mixed with components;

[0016] 5) adding the homogeneous precursor obtained in step 4) into a high-speed mechanical fusion machine, and after high-speed mechanical fusion, transferring into a vacuum carbonization furnace for vacuum carbonization, and grinding and crushing to obtain the nano-silicon-carbon composite negative electrode material containing nanofiber carbon.

[0017] Further, in step 4), the feeding speed is 500-1000 mL / h, and the spray inlet temperature is 180-220℃.

[0018] Further, in step 5), the high-speed mechanical fusion rotation speed is 2000 r / min, and the fusion time is 5-10 min; the vacuum carbonization temperature is 900-1100℃, and the vacuum carbonization time is 2-3 h.

[0019] According to the above technical solution, compared with the prior art, the nano-silicon-carbon composite negative electrode material containing nanofiber carbon and the preparation method thereof provided by the present application have the following excellent effects:

[0020] In the nano-silicon-carbon composite negative electrode material containing nanofiber carbon disclosed in the present application, due to the presence of nanofiber carbon, on the one hand, the nanofiber carbon can form a binding effect on the nano-silicon particles, and can better relieve the volume expansion; on the other hand, the nanofiber carbon can better improve the electrical conductivity of the material, avoid the loss of electrical contact of the nano-silicon particles due to volume change, and ultimately improve the cycle life of the material. BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced below. Obviously, the drawings in the following description are only embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of the provided drawings.

[0022] Figure 1 TEM photograph of the nano-silicon-carbon composite negative electrode material containing nanofiber carbon prepared in the present application.

[0023] Figure 2 Cycle life comparison curve of the silicon-carbon composite material prepared in Example 1 and Comparative Example 1 of the present application. DETAILED DESCRIPTION

[0024] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the embodiments of the present application and the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0025] The embodiment of the present application discloses a preparation method of a nano-silicon-carbon composite negative electrode material containing nanofiber carbon.

[0026] In order to better understand the present application, the following embodiments are further described below, but it should not be understood as limiting the present application. Some non-essential improvements and adjustments made by those skilled in the art based on the above content are also considered to fall within the protection scope of the present application.

[0027] Next, the technical solutions of the present application will be further described with reference to specific embodiments.

[0028] Embodiment 1

[0029] 1) 150 g of high-temperature pitch powder and 60 g of ethyl cellulose were weighed and added to 210 g of tetrahydrofuran for dissolution under sealed conditions, to obtain a mother liquor for forming polymer fibers with a solid content of 50 wt.%;

[0030] 2) 150 g of nano-silicon powder was weighed and added to 2850 g of deionized water and ultrasonically dispersed to obtain a nano-silicon powder dispersion liquid with a solid content of 5 wt.%, then 590 g of graphite and 50 g of sodium carboxymethyl cellulose were ultrasonically stirred and mixed uniformly to obtain a homogeneous dispersion liquid;

[0031] 3) The polymer fiber mother liquor prepared in step 1) was slowly injected into the homogeneous dispersion liquid obtained in step 2), and a high-speed disperser was used to continuously stir at a speed of 3000 rpm during the addition process, so that the pitch and ethyl cellulose were precipitated to form polymer fiber filaments, and the precursor liquid was uniformly mixed to obtain a homogeneous precursor liquid;

[0032] 4) The homogeneous precursor liquid obtained in step 3) was dried by a spray dryer, the feeding speed of the dryer was controlled at 500 ml / h, and the spray inlet temperature was controlled at 220℃, to remove water and tetrahydrofuran solvent in the precursor, and obtain a homogeneous precursor mixed with various components;

[0033] 5) The homogeneous precursor of step 4) was added to a high-speed mechanical fusion machine and mechanically fused at a speed of 2000 rpm for 10 minutes to enhance the mechanical bonding force of the components;

[0034] 6) The precursor material after mechanical fusion in step 5) is transferred into a vacuum carbonization furnace for carbonization treatment at 1100°C for 3h under vacuum condition, and then grinded and broken, to obtain a nano-silicon-carbon composite negative electrode material containing nano-fiber carbon.

[0035] Example 2

[0036] 1) Take 100g of high-temperature pitch powder and 40g of ethyl cellulose, add 210g to tetrahydrofuran, and dissolve under sealed conditions to obtain a mother liquor for forming high molecular fibers with a solid content of 40wt.%;

[0037] 2) Take 150g of nano-silicon powder, add to 4850g of deionized water, and ultrasonic dispersion to obtain a 3wt.% nano-silicon powder dispersion liquid, then add 680g of graphite, 30g of sodium carboxymethyl cellulose, and ultrasonic stirring to mix uniformly to obtain a homogeneous dispersion liquid;

[0038] 3) Slowly inject the high molecular fiber mother liquor prepared in step 1) into the homogeneous dispersion liquid in step 2), and continuously stir at a speed of 2000 revolutions / minute using a high-speed disperser during the injection process, so that the pitch and ethyl cellulose are precipitated to form high molecular fiber filaments, and the precursor liquid is mixed uniformly;

[0039] 4) The homogeneous precursor liquid obtained in step 3) is dried by a spray dryer, the feeding speed of the dryer is controlled at 1000ml / h, and the spray inlet temperature is controlled at 180°C, to remove water and tetrahydrofuran solvent in the precursor, to obtain a homogeneous precursor mixed with various components;

[0040] 5) The homogeneous precursor in step 4) is added to a high-speed mechanical fusion machine and mechanically fused at a speed of 2000 revolutions / minute for 5 minutes to enhance the mechanical bonding force of the various components;

[0041] 6) The precursor material after mechanical fusion in step 5) is transferred into a vacuum carbonization furnace for carbonization treatment at 900°C for 2h under vacuum condition, and then grinded and broken, to obtain a nano-silicon-carbon composite negative electrode material containing nano-fiber carbon.

[0042] Example 3

[0043] 1) Take 120g of high-temperature pitch powder and 40g of ethyl cellulose, add 160g to tetrahydrofuran, and dissolve under sealed conditions to obtain a mother liquor for forming high molecular fibers with a solid content of 50wt.%;

[0044] 2) Take 150g of nano-silicon powder, add to 3600g of deionized water, and ultrasonic dispersion to obtain a 4wt.% nano-silicon powder dispersion liquid, then add 650g of graphite, 40g of sodium carboxymethyl cellulose, and ultrasonic stirring to mix uniformly to obtain a homogeneous dispersion liquid;

[0045] 3) Slowly inject the high molecular fiber mother liquor prepared in step 1) into the homogeneous dispersion liquid in step 2), and continuously stir at a high speed of 2500 rpm with a high-speed disperser during the injection process, so that the asphalt and ethyl cellulose are precipitated to form high molecular fiber filaments, and the precursor liquid is uniformly mixed;

[0046] 4) Dry the homogeneous precursor liquid obtained in step 3) with a spray dryer, control the feeding speed of the dryer at 750 ml / h, and the spray inlet temperature at 200°C, remove the water and tetrahydrofuran solvent in the precursor, and obtain a homogeneous precursor mixed with various components;

[0047] 5) Put the homogeneous precursor in step 4) into a high-speed mechanical fusion machine and mechanically fuse at a speed of 2000 rpm for 8 minutes to enhance the mechanical bonding force of the components;

[0048] 6) Put the precursor material after mechanical fusion in step 5) into a vacuum carbonization furnace for carbonization treatment under vacuum condition at 1100°C for 3h, and then grind and crush to obtain a nano-silicon-carbon composite negative electrode material containing nano-fiber carbon.

[0049] Example 4

[0050] 1) Weigh 130g of high-temperature asphalt powder and 50g of ethyl cellulose into 270g of tetrahydrofuran and dissolve under sealed conditions to obtain a 40wt.% solid content mother liquor for forming high molecular fibers;

[0051] 2) Weigh 150g of nano-silicon powder into 2850g of deionized water and ultrasonic dispersion to obtain a 5wt.% nano-silicon powder dispersion, and then add 625g of graphite and 45g of sodium carboxymethyl cellulose and ultrasonic stir to mix uniformly to obtain a homogeneous dispersion liquid;

[0052] 3) Slowly inject the high molecular fiber mother liquor prepared in step 1) into the homogeneous dispersion liquid in step 2), and continuously stir at a high speed of 3000 rpm with a high-speed disperser during the injection process, so that the asphalt and ethyl cellulose are precipitated to form high molecular fiber filaments, and the precursor liquid is uniformly mixed;

[0053] 4) Dry the homogeneous precursor liquid obtained in step 3) with a spray dryer, control the feeding speed of the dryer at 800 ml / h, and the spray inlet temperature at 210°C, remove the water and tetrahydrofuran solvent in the precursor, and obtain a homogeneous precursor mixed with various components;

[0054] 5) Put the homogeneous precursor in step 4) into a high-speed mechanical fusion machine and mechanically fuse at a speed of 2000 rpm for 10 minutes to enhance the mechanical bonding force of the components;

[0055] 6) The precursor material after mechanical fusion in step 5) is transferred into a vacuum carbonization furnace for carbonization treatment at 1000°C for 3h under vacuum, and then ground and broken to obtain a nanosilicon-carbon composite negative electrode material containing nanofiber carbon. In addition, in order to further verify the excellent effects produced by the technical scheme of the present application, the inventors have also carried out the following tests, as follows:

[0056] Comparative Example 1

[0057] 1) 150g of nanosilicon powder is added to 2850g of deionized water and ultrasonically dispersed to obtain a 5wt.% nanosilicon powder dispersion liquid, and then 590g of graphite, 50g of sodium carboxymethyl cellulose are ultrasonically stirred and mixed uniformly to obtain a homogeneous dispersion liquid;

[0058] 2) The homogeneous precursor liquid obtained in step 1) is dried by a spray dryer, the feeding speed of the dryer is controlled at 500ml / h, the spray inlet temperature is 220°C, and the water and tetrahydrofuran solvent in the precursor are removed to obtain a homogeneous precursor mixture of the components;

[0059] 3) The homogeneous precursor of step 2) is added to a high-speed mechanical fusion machine and mechanically fused at a speed of 2000rpm for 10 minutes to enhance the mechanical bonding force of the components;

[0060] 4) The precursor material after mechanical fusion in step 3) is transferred into a vacuum carbonization furnace for carbonization treatment at 1100°C for 3h under vacuum, and then ground and broken to obtain a nanosilicon-carbon composite negative electrode material containing nanocarbon fibers.

[0061] Comparative Example 2

[0062] 1) 150g of nanosilicon powder is added to 2850g of deionized water and ultrasonically dispersed to obtain a 5wt.% nanosilicon powder dispersion liquid, and then 150g of high-temperature pitch powder, 60g of ethyl cellulose, 590g of graphite, and 50g of sodium carboxymethyl cellulose are ultrasonically stirred and mixed uniformly to obtain a homogeneous dispersion liquid;

[0063] 2) The homogeneous precursor liquid obtained in step 1) is dried by a spray dryer, the feeding speed of the dryer is controlled at 500ml / h, the spray inlet temperature is 220°C, and the water and tetrahydrofuran solvent in the precursor are removed to obtain a homogeneous precursor mixture of the components;

[0064] 3) The homogeneous precursor of step 2) is added to a high-speed mechanical fusion machine and mechanically fused at a speed of 2000rpm for 10 minutes to enhance the mechanical bonding force of the components;

[0065] 4) The precursor material after mechanical fusion in step 3) is transferred into a vacuum carbonization furnace and carbonized at 1100℃ for 3 hours under vacuum conditions. Then it is ground and crushed to obtain nano-silicon-carbon composite anode material containing nano-carbon fibers.

[0066] The nano-silicon-graphite composite anode material prepared in the embodiments of the present invention was used to fabricate anode sheets, assembled into 2032 coin cells, and the cycle life was tested. The material performance data are shown in Table 1, and the cycle life curves are shown in Table 2. Figure 2 As shown.

[0067] The battery cycle performance test method is as follows: first, discharge to 0.01V with a current density of 100mA / g, then discharge to 0.005V with a current density of 10mA / g, let stand for 3 minutes, and then charge to 1.5V with a current density of 100mA / g. This constitutes one cycle test of cycle performance.

[0068] Furthermore, the nano-silicon-carbon composite anode materials without nanofiber carbon from Comparative Examples 1 and 2 were assembled into 2032 coin cells for cycle life testing. The material performance data are shown in Table 1, and the cycle life curves are shown in... Figure 2 As shown.

[0069] from Figure 1 The TEM images show that the sample prepared in Example 1 clearly contains many fibrous carbon materials (nanofiber carbon), which can effectively bind the nano-silicon particles in the composite material and improve the conductivity of the material.

[0070] pass Figure 2 The cycle life curves of Example 1 and Comparative Example 1, as well as the data comparison and analysis in Table 1, show that the nanofiber carbon-containing silicon-carbon composite anode material prepared in this invention has a better cycle life.

[0071] Table 1

[0072]

[0073] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a nano-silicon-carbon composite negative electrode material containing nanofibrous carbon, characterized in that, The method specifically includes the following steps: 1) Weigh out high-temperature asphalt powder and ethyl cellulose according to the formula and add them to tetrahydrofuran for dissolution, and control the solid content in the range of 40-50 wt.% as the mother liquor for producing high molecular weight fibers, and set aside for later use. 2) Weigh out spherical nano-silicon powder according to the formula, add it to deionized water and disperse it by ultrasonication to obtain a nano-silicon powder dispersion with a solid content of 3-5 wt.%. Then add graphite and sodium carboxymethyl cellulose and stir ultrasonically to mix evenly to obtain a homogeneous dispersion. 3) Slowly inject the polymer fiber mother liquor prepared in step 1) into the homogeneous dispersion obtained in step 2). During the addition process, stir at a high speed of 2000-3000 r / min to precipitate asphalt and ethyl cellulose to form polymer fiber filaments, and at the same time mix evenly to obtain a homogeneous precursor liquid. 4) Spray dry the homogeneous precursor solution obtained in step 3) to obtain a homogeneous precursor in which all components are mixed; 5) The homogeneous precursor obtained in step 4) is added to a high-speed mechanical fusion machine, and after high-speed mechanical fusion, it is transferred to a vacuum carbonization furnace for vacuum carbonization, grinding and crushing to obtain the nano-silicon-carbon composite anode material containing nanofiber carbon. The solid solute in the precursor solution mainly consists of 10-15 wt.% high-temperature asphalt powder, 4-6 wt.% ethyl cellulose, 15 wt.% spherical nano-silica powder, 3-5 wt.% sodium carboxymethyl cellulose, and 59-68 wt.% graphite powder.

2. The method for preparing a nano-silicon-carbon composite anode material containing nanofiber carbon according to claim 1, characterized in that, The feeding rate in step 4) is 500-1000 mL / h, and the spray inlet temperature is 180℃-220℃.

3. The method for preparing a nano-silicon-carbon composite anode material containing nanofiber carbon according to claim 1, characterized in that, In step 5), the high-speed mechanical fusion rotation speed is 2000 r / min, and the fusion time is 5-10 min; the vacuum carbonization temperature is 900℃-1100℃, and the vacuum carbonization time is 2-3 h.

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